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Rust and Runout

Rust and Runout

Problem:

High speed pulsation, usually above 35mph, occurring shortly after brake job or tire service is performed (usually between 3,000 and 6,000 miles).

Cause:

One or more of the rotors installed with excessive runout. Generic specification being used by domestic OEMs is .002”. Excessive runout causes disc thickness variation (DTV) over time. The average for most vehicles is 3,000 to 6,000 miles. This number can vary up or down based on the variables involved.

Figure 28.1 Jacking

Rust on the hub’s mating surface is a leading cause of runout. The rust can form to a point where it actually pushes the rotor away from the hub even with the wheel bolted on (See Figure 28.1). This process has been termed “jacking”. It works much the same way as a tree root under a side walk. There are tremendous forces involved as the rust “grows” between the rotor and hub.

Solution:

Cleaning of the rotor and hub’s mating surfaces is a critical part of the brake job. The hub to rotor mating surface must be free of rust or runout induced DTV can occur shortly after the brake job. As little as .001” of rust at the outside edge of the hub will result in .002” to .004” of runout.

The method used to clean the hub will depend on the severity of the rust buildup. The hub’s mating surface can be a difficult surface to clean due to the wheel studs. The area between the wheel stud and hub centering flange is the most difficult area to gain access to. Here are the best methods to clean the hub’s mating surface.

Method 1 – Mild rust build up:

1. Use an angle grinder equipped with a scotch brite disc to clean the majority of the surface area. Get as close to the studs as possible and change the disc when needed.

2. Finish the process by using the tool shown in Figure 28.2 to clean the area around the studs. This tool fits over the wheel stud to allow easy cleaning of the hard to reach area of the hub. Figure 28.3 shows the finished result.

Figure 28.2 OTC Tool

Figure 28.3 OTC Tool Hub

Method 2 – Severe rust buildup:

The hub shown in Figure 28.4 will not be able to be cleaned effectively using the steps outlined above. The end result would look something like Figure 28.5. The OTC tool does NOT work on mild to heavy rust. It has a tendency to polish the rust instead of removing it. The most effective method is to use the steps below:

Figure 28.3 Rusty Hub

Figure 28.5 Polished Rust

1. Abrasive blasting is the most effective method for rust removal. There is a specialized blast cabinet available that allows cleaning of the hub while it is still on the vehicle. The tool uses a drawstring boot to allow the unit to be used on the vehicle as shown in Figure 28.6.

Figure 28.6 Rust Buster

2. Figure 28.7 shows the finished product. This is the same hub shown in Figure 28.4. This hub will not be the source of rust induced runout. While there are other methods that can be used to clean rusty hubs the method described above are the most effective. Other methods can be time consuming, yield a lower quality job and may not result in all of the rust being removed.

Figure 28.7 Finished Product

How to Verify Accuracy of Setup on Bench Lathe

How to Verify Accuracy of Setup on Bench Lathe

Problem:

Bench lathe induced runout is a leading cause of runout induced DTV pulsation comebacks.

Cause:

There are three main reasons for bench lathe induced runout. They are:

  • Arbor runout
  • Adapter condition
  • Not verifying accuracy of setup

This tip will cover the process called “Scratch Cut” which is used to verify accuracy of setup.

Solution:

All rotors and drums machined on a bench lathe should be scratch cut before machining. This is necessary to verify the accuracy of the lathe setup. Skipping this step can lead to machining runout into the rotor. The process of verifying the setup is commonly referred to as “Scratch Cut”.

  1. Position the bits approximately .” away from the outside edge of the rotor.
  2. Bring the outside bit in until it just touches the rotor. While holding the outer knob place the inner dial on zero. On lathes without this feature take note of the dial reading.
  3. Back the cutting tip away from the rotor a small distance and turn the lathe off.
  4. Observe the scratch cut. If the scratch cut is at least 50% around the rotor proceed with the machining process (Figure 27.1). If the scratch cut is less than 50% then the setup needs to be verified (Figure 27.2).

    Figure 27.1 More Than 50 Percent

    Figure 27.2 Scratch Cut First Cut Less Than 50 percent

  5. Two things will cause a scratch cut of less than 50%. The first is the rotor has runout and needs to be machined.
  6. The second is a problem in the setup. Adapter cleanliness, arbor runout and tightening of the arbor nut are the main causes of setup problems.
  7. To verify the setup loosen the arbor nut. While holding the inner and outer adapter rotate the rotor 180 degrees. Retighten the arbor nut. This process changes the relationship of the rotor and adapters.
  8. Turn the lathe on and then move the twin cutter in or out a small distance.
  9. Make a second scratch cut by turning the dial to zero. On lathes without this feature turn the dial into the same number as the first scratch cut. This process makes each scratch cut the same depth which makes comparing the cuts easier.
  10. Back the cutting tip off a small distance and turn the lathe off. Compare the two scratch cuts. If the problem is in the rotor the cuts should on top of one another (Figure 27.3).

    Figure 27.3 Scratch Cut Second Matching First

  11. A setup problem will cause the second cut to be in a different position from the first (See Figure 27.4). If this is the case disassemble everything and check for cleanliness, correct adapters and for nicks on the mating surfaces (See Figure 27.5). Do not proceed with the machining process until the scratch cuts are in the same position. Doing so will induce runout into the rotor.

    Figure 27.4 Scratch Cut Not Matching

    Figure 27.5 Clean Surfaces

Bonus Tip:

EVERYTHING machined on a bench lathe should be scratch cut to verify accuracy.

Read last week’s post on Bench Lathe Adapter Service.

Bench Lathe Adapter Service

Bench Lathe Adapter Service

Problem:

Reoccurring pulsation complaints (high speed pulsation occurring after 3,000 to 6,000 miles)

Cause:

Bench lathe induced runout

Solution:

Preventing the majority of bench lathe setup problems is a relatively easy process. It involves the following steps:

  1. Arbor Shaft Runout: Measure arbor runout and correct if necessary (Figure 26.1). The typical specification for arbor runout measured near the end of the arbor is .002”. If the runout is outside of acceptable, remove and clean the mating surfaces. If this doesn’t correct it consult your lathe manual.

    Figure 26.1 Arbor Shaft Runout

  2. Arbor Face Runout: Measure the arbor face runout (Figure 26.2). The typical specification for this measurement is .0005”. Correction of excessive arbor face runout will have to be performed using the lathe manufacturer’s procedures.

    Figure 26.2 Arbor Face Runout

  3. Hubless Adapter Arbor Mating Surface: The adapter show in Figure 26.3 is typical in many shops. Hubless adapters rely on the mating of the surface shown in Figure 26.3 and the arbor face to be accurate and true. With the buildup shown in Figure 26.3 it would be impossible for an accurate setup with this adapter.

    Figure 26.3 Dirty Adapter Face

  4. Correcting Arbor Mating Surface: To clean the small mating surface, place a piece of sandpaper on a flat surface and run the adapter’s small face up and down a few times while applying even pressure. The end result should look like Figure 26.4. Don’t worry about pits or indentations, these won’t effect the mating.

    Figure 26.4 Clean Adapter Face

  5. Indexing Adapter to Lathe: (This step is optional if the arbor face runout was .0000”.) If the arbor face runout was greater than zero then the hubless adapters will have to be indexed to the lathe before continuing. Some adapters have index marks cast into them while others don’t. If there is no index mark use a file to make an index mark on the edge of the small mating surface as shown in Figure 26.5.

    Figure 26.5 Adapter Index Mark

  6. Preparing Adapter for Machining: Install the adapter on the lathe and position the twin cutter to enable machining of the large mating surface as shown in Figure 26.6. Sometimes it will be necessary to remove the opposite tool holder to achieve the proper clearance.

    Figure 26.6 Twin Cutter Setup

  7. Machining Large Mating Surface: Remove only as much material as necessary to achieve a 360 degree cut. This usually only requires .002” to .005”. Make a slow cut to machine the large mating surface. This process makes this mating surface true to the lathe as shown in Figure 26.7.

    Figure 26.7 Finished Product

  8. Optional Adapters: The same procedure can be used on the optional adapters available for most bench lathes such as the composite rotor adapter shown in Figure 26.8.

    Figure 26.8 Other Adapters

The average bench lathe setup will take between 1 to 2 hours to perform the procedures listed above on all the adapters in the shop. Once this procedure is performed all that is necessary it to keep the small and large mating surfaces clean and free of nicks and burrs. If the arbor face had runout and index marks were used then the adapter and arbor index marks should be aligned each time the adapters are used.

Even after this procedure has been done it is still necessary to check the setup. This is done by performing what is known as “scratch cut”.

Brake Lathe Arbor – Checking & Correcting Runout

Brake Lathe Arbor – Checking & Correcting Runout

Problem:

Bench lathe induced runout is a leading cause of runout induced DTV pulsation comebacks.

Cause:

There are three main reasons for bench lathe induced runout. They are:

  • Arbor runout
  • Adapter condition
  • Not verifying accuracy of setup

This tip will cover checking and correction of the lathe’s arbor. If the arbor has excessive runout (> .002”), then everything machined on that lathe will have some runout.

Solution:

Proper care of the arbor and periodic measurement of arbor runout will eliminate the arbor as a cause of lathe induced runout. Follow the steps below to check and correct arbor runout.

Measuring Arbor Runout: (Ammco lathe shown, others similar)

  1. Lathes using tapered arbors use witness marks to indicate the most accurate fit of arbor to spindle. These marks are made at the factory after the arbor is matched to the lathe. Verify these marks are aligned as shown in Figure 25.1

    Figure 25.1 Witness Marks

  2. Position the dial indicator as shown in Figure 25.2.

    Figure 25.2 Dial Indicator Setup

  3. Use the draw bar nut to rotate the spindle while watching the dial indicator. It is best to use a socket and ratchet when performing this step. Use a smooth 360 degree rotation for the most accurate measurement. If arbor runout is within specifications (generic no more than .002” with the closer to zero the better) no service is needed. If outside of specifications follow the steps below.

Correcting excessive arbor runout:

  1. Remove arbor. Inspect arbor and spindle taper(s) for chips or rust buildup (Figure 25.3). The tapered surfaces of the spindle should be cleaned using a fine to medium steel wool. The arbor’s tapered surface(s) can be cleaned using a wire wheel.

    Figure 25.3 Rusted Taper

    NOTE: Do NOT use sandpaper, emery cloth or anything that could remove metal. The taper surfaces determine the arbor’s fit and changing them in any way could result in permanent damage to the accuracy of these surfaces.

  2. Use a clean rag to wipe all mating surfaces before installing the arbor. Put a light coat of WD40 or similar treatment on the tapered surface(s) before installing. This will help prevent rusting.
  3. Align the witness marks and tighten the arbor nut or draw bar to specifications. This is usually around 50-60ft lbs.
  4. Repeat steps 1 to 3 under “Measuring runout” above to check arbor runout. If less than .002” process completed. If not, follow the steps below to determine the cause.

Determining source of excessive arbor runout:

  1. Rotate arbor until dial indicator is at its highest reading. This is the point of greatest runout. Use a magic marker to mark the point on the arbor as shown in Figure 25.4. This mark will be used to determine if the arbor is the source of the any excessive runout.

    Figure 25.4 Arbor High Spot

  2. Loosen the arbor and rotate it 1/8 of turn clockwise and tighten the drawbar. Measure arbor runout.
  3. If run-out is .002″ or less, make a mark on the arbor at the spindle witness mark.
  4. If more than .002″ runout is indicated, loosen the drawbar, rotate the arbor 1/8 turn in the spindle and retighten the drawbar.
  5. Recheck the run-out.
  6. If it is still more than .002” repeat step 4 and 5 until .002” or less runout is achieved. Then mark the arbor to the spindle witness mark.
  7. If the runout is still greater than .002” after the arbor has been rotated 360 degrees, rotate the arbor until the dial indicator shows the maximum runout reading. Check to see if the magic marker reference mark placed on the arbor in step 1 is aligned with the dial indicator plunger. If the two are aligned, the arbor is bent and will have to be replaced.

Note: Some older lathes may not have a witness mark. Dial indicate the arbor and mark both the arbor and spindle.

How to Diagnose Excessive Disc Thickness Variation (DTV)

How to Diagnose Excessive Disc Thickness Variation (DTV)

Problem:

Determining if one or more rotors has excessive DTV

Cause:

The average specification for disc thickness variation (DTV) is .0005” (See Figure 24.1). The maximum allowable variation in thickness on a rotor is 5 ten thousandths of an inch. This dimension is too small to measure accurately at the shop level.

Figure 24.1 Average DTV

Most publications give instructions for measuring DTV. The typical steps involve making 6 to 8 measurements at a certain distance from the edge of the rotor and then comparing these measurements to one another. If they vary by more than .0005” the rotor has excessive DTV. Measurements this small can only be accurately done in a laboratory environment.

Solution:

The only effective method to determine if one or more rotors has excessive DTV is by the symptom it produces. Excessive DTV is the leading cause of high speed pulsation complaints.

Excessive DTV is usually more pronounced when stopping from speeds above 35mph. The changing thickness of the rotor causes the caliper piston to move in and out. The movement of the caliper piston causes fluid movement in the hydraulic system which is felt in the brake pedal.

If the vehicle is exhibiting high speed pulsation then one or more of the rotors has excessive DTV. If the vehicle is disc/drum then both front rotors should be serviced according to their thickness and condition.

If the vehicle is equipped with 4 wheel disc brakes use the location of the vibration to help pinpoint front or rear. If the steering wheel and/or dashboard shake in addition to the brake pedal the problem is related to one or both front rotors. If the vibration is in the seat or floorboard it is most likely a rear problem. DTV is more common on front disc brakes than rear.

BONUS TIP:

You CANNOT measure thickness variation at the shop level. You must rely on the symptom it produces to know whether you have it.

How to Measure Rotor Runout

How to Measure Rotor Runout

Problem:

Accurately measuring installed runout

Cause:

Runout measurement is not being performed on a regular basis so many technicians do not know how to perform it.

Solution:

The dial indicator is used primary to measure rotor runout. In can also be used to measure arbor runout on the bench lathe, wheel bearing play and hub runout. Accurate measurements depend on proper use of the tool. The following steps outline the proper use of the dial indicator.

Attach flexible mount to vise grips. There are three mounting holes in the mounting block. The end one is usually the best one to use when possible.

Note: Make sure the flexible mount is screwed in tightly to the vise grip mount.

Locate a solid mounting point on the vehicle. Some examples would be the caliper mounting bracket, pad rails, lower strut mounting bolt, steering arm. Do not mount to anything that is not stationary in reference to the rotor (See Figure 23.1).

Figure 23.1 Vise Grip Mounted

On hub style rotors there must not be any bearing play. If excessive play is present adjust bearing before measurement. Hubless rotors have to be secured with spacers and lug nuts. On a 5 lug hub use at least 3 lug nuts. On a 4 lug hub use 2 opposite lugs with spacers. Where possible the lug nuts should be installed backwards with the flat sides against the spacers.

Attach the dial indicator by loosening the clamp screw. Tighten the clamp screw to a point where the dial indicator can be moved around easily.

With the red handle pointing directly in line with the base of the flexible mount , take the slack out of the flexible mount by turning the adjusting screw clockwise (See Figure 23.2).

Figure 23.2 Indicator Clamp

Locate the dial indicator plunger as shown in Figure 23.3. The tip should be about 1/4” from the edge of the rotor. It should be located on a smooth portion of the rotor. If necessary, take the runout reading on the inner surface of the rotor. The plunger should extend out of the housing and the contact tip should be at a slight angle that is in line with the edge of the rotor (See Figure 23.3).

Figure 23.3 Closeup of Needle

While holding the indicator in this position, rotate the red tension handle 180 degrees or until enough tension is present to hold the unit stationary.

Note: Make sure the tip of the indicator is screwed in all the way or vibration will occur during the reading.

Runout can now be taken. Rotate the rotor in the direction the dial indicator tip is pointing.

Watch the needle for the lowest and highest number reached during one revolution of the rotor. The runout is the difference between these two numbers. For example, if the lowest reading was 65 and the highest was 69 the runout is .004” (See Figure 23.4).

Figure 23.4 Reading

If you want to use the zero feature of the indicator rotate the rotor until the lowest reading is obtained. Loosen the set screw and rotate the black dial unit the needle points to zero. Rotate the rotor one complete revolution and note the amount of runout. If done correctly the needle will start and stop at zero without going below it.

Bonus Tip: 

It takes less than 60 seconds to measure rotor runout and KNOW whether the runout will be an issue in that vehicle coming back with a pulsation complaint.

Reoccurring Pulsation

Reoccurring Pulsation

Problem:

High speed pulsation, usually above 35mph, occurring shortly after brake job or tire service is performed.

Cause 1:

One or more of the rotors were installed with excessive runout. Generic specification being used by domestic OEMs is .002”. Excessive runout causes disc thickness variation (DTV) over time. The average for most vehicles is 3,000 to 6,000 miles. This number can vary up or down based on the variables involved.

Cause 2:

Insufficient clearance between inboard and outboard brake pads and rotor’s friction surface. The closer the brake pads are to the rotor’s friction surface the smaller the amount of runout needed to produce disc thickness variation (DTV).

Solution 1:

Rotors must be installed with runout less than vehicle’s specifications in order to eliminate runout induced DTV. There are 2 options to perform this.

Option 1: Use an on-the-car lathe to machine the rotors true to the hub. Make sure to index the rotor to the hub if removing it after the machining process. Make sure to properly torque the wheels using the method described in step 6 below.

NOTE: When performing on-the-car machining on vehicles equipped with ABS make sure none of the machining chips accumulate on the magnetic sensor tip. This could trigger false activation of the ABS or fault codes. See Figure 22.1

Figure 22.1 Lathe Chips

Option 2: If using a bench lathe to perform off the vehicle machining follow these steps:

  1. If resurfacing the rotor(s) use proper machining techniques and make sure the lathe is in good working condition. On hubless rotors make sure to clean the mating surfaces with an appropriate tool. Scratch cut all rotors to ensure accurate setup.
  2. Clean the rotor before installing on vehicle to prevent machining dust from contaminating brake pads.
  3. Before installing hubless rotors, clean the hub mating surface using an appropriate tool(s). Failure to properly clean this surface can prevent achieving the proper installed runout.
  4. When installing new or machined hubless rotors the installed runout should be checked. Using spacers on the studs tighten all lugs to the proper torque using the correct sequence. Measure runout. If runout is not less than manufacturer’s specification index the rotor on the hub to achieve the lowest amount of lateral runout.
  5. Before indexing mark the high spot on the rotor and hub using a magic marker or paint stick as shown in Figure 22.2. Indexing involves removing the rotor and rotating it one or two lugs and reinstalling. Repeat this until the installed runout is below specification. If runout is out of specifications and does not change as the rotor is rotated check to see if the high spot moves with the rotor or stays with the hub. This will identify the cause of the runout.

    Figure 22.2 Indexing

  6. Properly torque the wheel lugs using either a hand torque wrench or torque stick sockets. When torquing wheels use a step torque process. To step torque the lugs tighten all lugs to half the normal torque using proper sequence and then fully torque lugs using same process. Make sure your impact has been calibrated before using torque sticks.

Solution 2:

Look closely at Figures 22.3 & 22.4. Both rotors shown have the same runout but what they don’t have is the same gap between the pads and rotor. The gap between the pads and rotors in Figure 22.3 is much smaller than that of Figure 22.4. The smaller the gap the more sensitive the vehicle will be to runout induced DTV. Remember the wear of the high and low spots occurs during both brake apply and release. If something in the caliper assembly is preventing a full or complete release of either the outboard or inboard pad that wheel will be more susceptible to this problem. Improper release of either pad could make even those rotors at or below .002” prone to this problem.

Figure 22.3 Small Pad to Rotor Gap

Figure 22.4 Large Pad to Rotor Gap

Effective inboard pad release will be effected by two types of conditions. The first of these involves how well the piston releases. A piston that does not return as far as it should reduces the gap between the inboard pad and rotor. Mileage, brake fluid condition, dust boot seal integrity all can impact the piston’s ability to release properly. The second condition that can effect the release of the inboard pad involves how easy the pad can move in relationship to the caliper mounting bracket, knuckle or slide rails. If the inboard pad binds then complete release will not take place.

Outboard pad release can be impacted by two categories of failures as well. The most common of these is the slide hardware. If the caliper housing is not free to move on its mounting hardware then outboard pad release will be effected. The other category is the same as for inboard pad release, that is anything causing the outboard pad to bind where it contacts the bracket, knuckle or slide rails.

Nothing new about what impacts inboard or outboard pad wear but understanding its influence on the issue of runout induced DTV is a fairly new concept. The moral of the story is short cutting quality brake work impacts more than just pad life. The old “pad slap” has more chances to come back and haunt you than what you might have considered. Remember just because the caliper applies and releases doesn’t guarantee its doing it as effectively as it should. Look at the big picture when doing your brake inspection. A few more minutes covering the details up front will pay big dividends in the long run. A saying I like to use sums it all up – “I would rather be paid today for what is wrong with the vehicle than have to give it away tomorrow”.

More Info: The fact that excessive runout is the leading cause of reoccurring pulsation should not be anything new. The principal is easy, too much runout on fixed bearing vehicles causes the high and low spot of the rotor to scrape against the pads. This scraping occurs during both non-braking and braking. Over time the high and low spots are worn thinner than the other portions of the rotor. This difference in thickness is known as disc thickness variation or DTV (See Figure 22.5). It is also called parallelism. The two friction surfaces of a rotor are supposed to be parallel to one another to within a certain tolerance. The average value for this specification is .0005”. As little as 5 ten thousands of an inch or another way to say it would be ó of one thousandth of an inch tolerance is all that is allowed.

Figure 22.5 Disc Thickness Variation (DTV) Views

If DTV is in excess of acceptable limits the thin spots pass between the pads during brake apply causing the caliper piston must move out to take up the gap. The thick portions of the rotor push the piston back. The in and out movement of the piston causes the pedal to pulsate especially at speeds above 35mph. What has been stressed is the importance of getting the rotor’s installed runout to acceptable levels. Most domestic OEMs are agreeing that this amount is .002” or less. While this is definitely the most important aspect of curing the reoccurring pulsation it is not the only thing to consider. There are other factors that will contribute to the vehicle’s sensitivity to this.

Bonus Tip: 

Discard the myth that reoccurring pulsation complaints are caused by warped rotors due to overheating.

Rotor & Drum Specification Accuracy

Rotor & Drum Specification Accuracy

Problem:

Not all of the specifications provided are 100% accurate.

Cause:

Consolidated specification sources often make mistakes when compiling the information from the various manufacturers.

Solution:

Verifying accuracy of rotor and drum specifications.

A close look at Figure 21.1 shows the 1998 Buick Skylark vehicle listed having different machine to specifications. Depending on the circumstances using the wrong specifications could result in machining a rotor that should have been replaced or selling one that could of been serviced.

Figure 21.1 Rotor Specs

You are making some pretty important decisions based on the specifications you get out of your specs book – you need to make sure they are accurate. Read our previous post on Rotor & Drum Specification Issues as well.

The best method is to find two specifications from different information providers that are the same. The most accurate sources are the rotor itself, information providers such as Mitchell or All Data, and specifications provided by the parts manufacturers.

Rotor & Drum Specification Issues

Rotor & Drum Specification Issues

Problem:

Determining a rotor’s or drum’s serviceability based on available specifications.

Cause:

Many manufacturers do not supply both machine to and discard thickness

Solution:

No Machine to Specification Listed

Many vehicles no longer provide a machine to specification. This does not mean the rotor is not serviceable. Most of these rotors are allowed to be machined to the discard specification. This is not a practical procedure in a shop environment. This is especially true in the states where there are safety inspections performed. It is possible to perform a brake job and have the vehicle fail a state inspection only a couple of months after the brake job.

Figure 20.1 shows an example of this. In this example no machine to specification is given. Instead a “NS“ is listed. The “NS” is short for “Not supplied by manufacturer”.

Figure 20.1 No Machine To

In this case the machine to is calculated by added .015” to the discard specification provided. In the case of the 98 to 2000 Mountaineer the discard listed is .980”. Adding .015” to this would yield a machine to thickness of .995”.

No Discard Specification provided

In Figure 20.2, no discard specification is given. Instead a footnote number is listed. The footnote listed is number 2 which can be found at the end of the make section. Footnote 2 says:

“Discard when thickness is smaller than the minimum machining specification”

20_2_footnote example_rgb

This means the discard and machine to specification are the same number. This would not be practical for the customer. If the rotor were machined down to the machine to it would go beyond service in a very short period of time. Another brake inspection or a state inspection would result in the rotor being under specifications after just being serviced. The industry has adopted the position of creating a revised machine to specification by adding .015” to the number provided. In the case of the 2001-99 Cougar the machine to listed is .874”. Adding .015” to it will bring the revised machine to up to .889”. This is number you would use to determine whether the rotor can be machined or not. The .015” allows for normal rotor wear during the life of the friction material.

NOTE: Although it is best to use the aftermarket approach, it is acceptable to machine these rotors down to the machine to specification listed. The invoice should be marked “rotors at minimum machining/discard” to avoid future problems.

The same holds true for brake drums. There is no drum discard specification provided for the vehicles in the highlighted box. Instead, a footnote number 3 is listed and that footnote says:

“Discard when diameter is greater than the maximum machining specification”

This means the maximum machining diameter and discard diameter are the same for these vehicles. If the drum were machined up to the machine to it would go beyond service in a very short period of time. Another brake inspection or a state inspection would result in the drum being over specifications after just being serviced. The industry has adopted the position of creating a revised machine to specification by subtracting .015” from the number provided. In the case of the 2001-99 Cougar the machine to listed is 9.040”. Subtracting .015” from this value would result in a machine to specification of 9.025”. This is the number you would use to determine whether to machine the drum or not.

Bonus Tip:  ‘NS” does NOT mean “Not Serviceable” as some technicians have been led to believe. It means “Not Supplied”.

How To Determine if A Rotor Can Be Serviced

How To Determine if A Rotor Can Be Serviced

Problem:

Whether a rotor can be serviced is based on its dimensions and condition. The decision to service or replace the rotor may be based on incorrect information leading to over or under selling.

Cause:

The dimensions of a rotor determine whether it can be machined, replaced or in some cases left alone. Not understanding the meaning of the dimensions involved in making these decisions can lead to a rotor being machined when it shouldn’t be or a new rotor sold when the old rotor was still serviceable.

Solution:

Understanding all of the critical dimensions of a rotor will allow accurate determination of the rotor’s condition and what type of recommendation should be made. Here is a description of the important dimensions of a rotor:

Nominal Thickness:

Nominal thickness is the thickness of the rotor when it is new. This thickness is not usually used on a daily basis but is listed in most specification books.

Machine to thickness:

This is the thinnest a rotor can be machined to and still be put back into service. The purpose of having a machine to thickness is to provide enough rotor material to last the life of one set of pads. The assumption is that if the pads are replaced and the rotors are over machine to they should not experience enough wear to allow them to go below discard thickness through the life of that set of pads. The average difference between nominal and machine to thickness is .050“ to .060“. The typical difference between machine to and discard (explained below) is .015“. See Figure 19.1.

Figure 19.1 Rotor Dimensions

There is a common myth concerning what are usually called throwaway rotors. The myth states that most rotors on late model vehicles have no meat on them and are not meant to be machined or can‘t be. This is not true. Again, the average rotor provides .050“ to .060“ with some giving as much as .100“ between nominal and machine to thickness. With the average machining taking off .010“ to .015“ there is usually always room for one machining and sometimes 2. The only true throwaway rotors are marked like the one in Figures 19.2 & 19.3. The footnote (3) on this BMW denotes the rotor should be replaced not machined. True throwaway rotors are marked in this fashion.

Figure 19.2 BMW Throwaway Rotor Footnote

 

Figure 19.3 BMW Throwaway Rotor Listing

Discard Thickness

The discard thickness of a rotor is the thickness at which the rotor should be replaced. The common understanding of the definition of discard thickness is that it is a heat related dimension. It is generally understood that if a rotor is at or below discard thickness it cannot dissipate the heat generated. This is not correct. Discard thickness is the thinnest a rotor can wear to so that if the brake pads wear to nothing the caliper piston won‘t fall out of the caliper housing. It has nothing to do with heat. See Figure 19.4.

Figure 19.4 Discard Thickness

This definition makes sense if you apply it to what most technicians have experienced over the years. The average technician has serviced many vehicles with a rotor at or below discard and the vehicle stopped fine. The technician usually doesn‘t know the rotor is at or below discard until they measure the rotor and compare the measurement to the specifications.

Parallelism (Disc Thickness Variation, DTV)

The two friction surfaces of a rotor are designed to be parallel to one another within a certain specification. The allowable tolerance is known as parallelism. It is also known as the rotor‘s disc thickness variation or DTV. See Figure 19.5.

Figure 19.5 DTV Views

Other rotor factors

A common question presented about rotors involves the thickness of one friction disc to the other on vented rotors as shown in Figure 19.6. There is not a published specification for the allowable tolerance for the difference in the thickness of one disc to the other. Some rotors are actually designed intentionally with different thickness discs. It is generally accepted that small differences are acceptable and are either intentional or a result of manufacturing variations.

19.6 Friction Discs

When machining a rotor, the thickness of one friction disc to the other should be taken into consideration. For example, if a rotor is gouged on one friction surface due to metal to metal contact with the brake pad but not the other, it could be possible to machine the gouge out and the rotor still be over machine to thickness. The problem would be that the gouged friction disc would be considerably thinner than the opposite disc. When faced with this situation common sense is the only guide. If the gouge is deep enough to result in having to remove a considerable amount of material it is probably best to replace the rotor.

Corrosion and rust can also have an impact on the rotor‘s ability to function correctly. Figure 19.7 shows a rotor that has clogged vent holes due to rust buildup. This rotor is thick enough to machine but the rust will prevent proper cooling. Likewise the rotor pictured in Figure 19.8 has experience enough corrosion to actually weaken its structural integrity.

19.7 Plugged Fins

Figure 19.8 Structural Damage

The rust has eaten away at the thickness of the cooling fins. This condition could result in the two halves of the rotor separating resulting in a catastrophic brake failure. Always perform a thorough visual inspection of the rotor to determine its condition and serviceability.

Rotor thickness is not very exciting but crucial in doing a good brake job.

What To Do About Brake Noise

What To Do About Brake Noise

Problem:

Vehicles returning with complaints of brake noise

Cause:

One thing that both customers and technicians have in common is they both hate dealing with brake noise. Customers find brake noise annoying and embarrassing. Technicians find brake noise frustrating and unproductive. Unfortunately, both groups find brake noise all too common. Most shops that perform brake service will tell you that brake noise represents the most common reason for brake comebacks.

Brake noise is the layman’s description of the symptom. Brake noise is actually vibration that is occurring at a frequency that is audible to the human ear. All brakes make noise or vibrate. The difference is that most brakes operate at a frequency that we can’t hear.

Solution:

Well, then, its simple, to prevent or fix brake noise all we have to do is make sure the brakes operate (or vibrate) at the right frequency. In theory it is that simple but in real life there is often much more to it than meets the eye. There are many variables involved in the equation that can result in brake noise. Understanding these variables is the starting point of preventing brake noise complaints.

Notice I used the word “prevent” not fix. This should be our primary goal. If we get a handle on how to prevent noise complaints from occurring then we will be better able to handle any comebacks. Most brake noise complaints involve disc brakes so we are going to focus our attention on disc brakes. As the brake pedal is applied and the disc brake pads are squeezed against the rotor, vibration is produced. The points where the vibration takes place are pictured in Figure 18.1. Vibration can occur between the:

  1. Pads and rotor
  2. Pads and caliper
  3. Caliper and knuckle or mounting bracket
  4. Pads and knuckle or mounting bracket
  5. Caliper and mounting hardware

    Figure 18.1 Brake Noise

The number of points where the vibration occurs will vary with the type of disc brake used. The type of disc brake will also determine which causes will be more common. As you can see from the list, the prevention of most brake noise complaints will boil down to performing quality brake service and using quality parts. We will discuss each of these potential problem spots and cover what should be done to prevent them.

• Rotor Finish – the smoothness of the friction surface of the rotor is important in preventing brake noise complaints. This is especially true right after a brake job is performed. The smoother the surface at the start of a brake job the lower than chances for brake noise.

• Friction material – It is commonly felt that the brake pad is the leading culprit in creating brake noise. While in some cases this is true it is not a blanket statement that can be applied to all cases. If you have access to Mitchell On Demand or All Data you might want to take some time and look through some of the TSB’s (Technical Service Bulletins) dealing with brake noise that have been published by the various OEMs. If you do, you would see that changes in brake friction material is often used to help combat brake noise complaints. If you take a closer look, you would see that it is not the only method used. How does this relate to you and the friction material you are using? My position on aftermarket friction and brake noise is this – if you use a quality product from a reputable supplier then you should not have noise problems with MOST vehicles. Quality pads should be designed after the OEM pad. This means they should have shims, tapered edges or dust slots if the OEM pads were equipped with these features.

  Pad shims – Pad shims are used as an insulator between the pads and caliper. This serves to change the frequency of the vibration so brake noise is eliminated. The shims could be attached to the brake pad or they could be supplied as separate parts. Make sure your replacement pads are shimmed to match the OE pads and when servicing vehicles with separate shims either reuse the shims if in good condition or replace them. Do not reuse shims where the protective coating has worn off or if the shims are rusting and flaking. Do yourself a favor and add the cost of replacing the shims into your estimate now instead of giving them away later.

  Pad hardware – It used to be that imports were the only vehicles using pad anti-rattle hardware but now disc brake assemblies similar to that shown in Figure 18.2 have become the standard on many domestic vehicles. The pads “snap” into the caliper mounting bracket and are held in place by various clips. The caliper straddles the assembly and serves only to provide the squeezing of the pads against the rotor. The caliper mounting bracket absorbs all of the braking force and maintains the pad’s position. The anti-rattle hardware applies tension to the pads so they fit snugly against the mounting bracket. These clips are essentially small springs made of stainless steel. They are subjected to the same heating and cooling as rear brake hardware. How many of you are strong believers that the brake shoe hardware should be changed with each set of shoes? What’s the difference with the front hardware? Simply cleaning and reinstalling it won’t be good enough in many cases. Some add an extra step of “re-tensioning” the clips by bending the tabs slightly. This may work for a short time but won’t provide a long-term solution. Suggesting the replacement of this hardware with each pad replacement is something you should consider. The hardware can be pricey and you should explain to the customer why you are suggesting it. If they decline and have a noise problem later then you are in a better position than if you said nothing about the hardware.

Figure 18.2 Caliper and Mounting Bracket

  Caliper hardware – Most vehicles use floating calipers. The rubber bushings or sleeves in these calipers allow the caliper to move freely on brake apply and release. They wear over time and can increase the chances for brake noise. Careful inspection should be done and replacement should be suggested or required based on the findings. If the bushings or sleeves are too loose fitting the caliper will be allowed to move too much (See Figure 18.3). This will increase the chances for a brake noise problem especially if other problems are present. Again, if the customer declines the service, mark the invoice accordingly. If a noise comeback occurs, you will have set the groundwork for what needs to be done. It’s a better position to be in then having nothing to fall back on.

18_3_worn rubber_rgb

Figure 18.3 Rubber Busing is Worn

  Cleaning & lubing – The amount and type of cleaning you will have to do will vary with the type of vehicle being serviced and the area of the country you live in. Some vehicles have only a few key areas that need to be cleaned when servicing the disc brakes while others require considerable more effort. If you work in the south or out west then you won’t have to deal with too much rust like those of us in the snow belt. For more information on cleaning and lubing see our blog post.

  Pad staking – Some outboard pads are designed to be “staked” to the caliper. This staking holds the pad firmly in place and prevents vibration. Older domestic RWD vehicles use outboard pads that stake to the caliper using small tabs as shown in Figure 18.4. This style of pad is best staked off of the caliper. Bend the tabs on the pad until a press fit is needed to install it. Use a pair or channel locks to press it onto the caliper using a piece of cardboard to protect the friction material. Some General Motors vehicles require a different procedure to stake the outboard pad. The pads pictured in Figure 18.5 are first installed on the vehicle. Next a chisel is driven between the hat of the rotor and the base of the pad to hold the pad against the caliper. Now, have an assistant apply and hold the brake pedal. This will hold the pads in place while you perform the staking. The tabs should be bent over at about a 45-degree angle. Release the brakes and check the tightness. No movement should be felt between the pad and caliper.

Figure 18.4 Stake Off Caliper

Figure 18.5 Stake On Caliper

  Pad break in – Starting the mating of the pads to the rotor and getting the brake job off on the right foot is critical to the long term success of the brakes. See our blog post for more information on the proper break-in procedures.

My experience is if you apply the information above and the information contained in the related articles mentioned you will eliminate 8 of 10 brake noise comebacks. If that is the case what do you do with the other 2? This is when you consider the friction material as the possible culprit. If I am involved in a brake noise comeback, I first look at whether any of the steps above have been skipped or not performed properly, in other words was a quality brake job performed. If the answer is yes, then I consider an alternate pad.

Brake pad noise is one of those things that annoys everybody so it is better to do the best job possible to prevent it and we hope this post helps you with that.

What is Friction Break In and How To Do It

What is Friction Break In and How To Do It

Problem:

Brake noise complaints or lack of stopping power shortly after brake job

Cause:

Not performing a proper break-in after performing brake service

Solution:

Once the job has been completed, a test drive should be performed. The test drive has two goals. The first is to make sure the brake system is operating properly. The other reason a test drive is performed involves mating the pads to the rotors. This can be called “break in” or “burnishing” the pads. It doesn’t matter what you call it, it matters that you do it. Depending on whom you talk with the number of stops you should make will vary. A good average is 10 to 12. To mate the pads to the rotors make 10 to 12 stops from about 30 to 35 mph down to about 10 mph. Allow about 30 seconds between stops for cooling.

When you deliver the vehicle to the customer, advise them not to do any severe braking for the first couple of hundred miles. This includes towing or hauling and having them anticipate their stops when possible.

Management is trying to influence two types of customers. One group of customers feels the best check for quality brake work is to go out an lock em up. Too many of this type of stop right after the job is done can have irreversible effects on the performance of the brake job. The other group of customers are those that will leave your shop with the brand new brake job and go on vacation. Not catching that customer who is leaving for vacation the day after your brake job with everything but the kitchen sink in tow can cost you big time. Talk to and educate your customers, it will benefit both of you in the long run.

Some OEMs endorse the same steps on their new cars. Figure 17.1 shows the new vehicle break-in page from a owners manual on a late model GM vehicle. You can see the same steps as stated above covered in points 2 & 3.

Figure 17.1 New Vehicle Break In

At times it will not be practical to perform the second part of the break-in process. Asking fleet customers to not tow or haul for 200 miles is not practical. In these cases, try and at least double the number of stops taken in the first step to bring the process closer to completion.

Remember that proper friction break in is part of any quality brake job.

What are some of your thoughts on brake pad break-in? We would love to hear them and any other thoughts you might have on what we should include in our Tech Tricks Tuesday posts.

Slide Rail Repair

Slide Rail Repair

Problem:

Worn slide rails on vehicles equipped with pad slide rails (See Figure 16.1)

Figure 16.1 Worn Slide Rail

Cause:

The slide rails wear due to the tremendous forces during braking and lack of lubrication. The constant force of the brake pads being pushed into the slide rails during braking combined with the constant back and forth movement of the brake pads causes “dimples” to wear in the most used areas.

Solution:

In theory the only fix to this problem is to replace the part with the worn slide rails. Depending on the application this will either be the caliper mounting bracket or the entire steering knuckle. Neither of these repairs is practical.

The slide rails can be repaired following the steps below:

  1. Clean the slide rail surfaces down to bare metal taking care not to remove good material. (See Figure 16.2

    Figure 16.2 Cleaned Side Rail

  2. Using a MIG welder fill the worn spots making sure to use the necessary settings to get good penetration. Try to avoid building the area up to high. The more buildup the more work. (See Figure 16.3)

    Figure 16.3 Welded Slide Rail

  3. Using an angle grinder with an abrasive sanding disc rough in the repaired area. Use the surrounding surfaces as a reference.
  4. When close, use a Scotch-Brite disc to perform the finish work. The area can be checked using a straight edge. (See Figure 16.4)

    Figure 16.4 Completed Side Rail

  5. Check the final repair by sliding the pad the full length of the slide rails while checking for binding.

BONUS TIP:

Using this process will save your customer money, provide a legitimate profit for the shop, and restore the knuckle to like new condition.

Next week we will discuss Friction Break In and last week we discussed How to Fix Binding Calipers on Ford Light Trucks. Enjoy the reading material and keep coming back for more Tech Tricks Tuesday.

How To Fix Binding Calipers on Ford Light Trucks

How To Fix Binding Calipers on Ford Light Trucks

Problem:

Calipers binding causing premature outboard pad wear

Cause:

This problem can have two different causes. They are:

  1. Using petroleum based lubricants on this design caliper can cause the rubber in the keepers to swell. Swelling of the rubber will cause the caliper to bind on release.
  2. Buildup of rust and corrosion between the caliper/keeper/knuckle or failure to properly clean the mating surfaces of the caliper/keeper/ knuckle.

Solution:

The solutions to each of the causes listed above are:

  1. Ford states in TSB 98-5A-13 to use only a high quality silicone lubricant when servicing these trucks. Silicone will not effect the rubber and serves to repel the water.
  2. Whenever servicing the brake pads on this type of caliper make sure to clean all mating surfaces before applying the lubricant.

More Info:

Many Ford light trucks and SUVs use the sliding caliper pictured in Figure 15.1. When performing service on this type of caliper it is important to use the correct type of lubricant.

Figure 15.1 Ford Sliding Caliper

Ford service information states to use only a high quality silicone lube. Use of any petroleum based lubricant will cause the rubber core of the keep to swell. The swelling will restrict caliper movement and result in outboard pad wear. Moly-lube, anti-seize, white lithium grease and most other commonly used lubricants are petroleum based and should never be used on brake rubber parts. Use of the silicone lube will not only prevent damage to the rubber core of the keeper but silicone also repels water.

Remember to keep coming back for our Tech Tricks Tuesday Blog Posts and to read those past posts to stay up to date on tricks that we have learned from our years of experience.

How to Clean and Lubricate Brake Parts to Help Prevent Comebacks

How to Clean and Lubricate Brake Parts to Help Prevent Comebacks

Problem:

Premature wear and brake noise comebacks

Cause:

Sometimes the cause relates to the quality of the cleaning and lubing

Solution:

The amount and type of cleaning you will have to do will vary with the type of vehicle being serviced and the area of the country you live in. Some vehicles have only a few key areas that need to be cleaned when servicing the disc brakes while others require considerable more effort. If you work in the south or out west then you won’t have to deal with too much rust like those of us in the snow belt. We commonly have to deal with brackets that look like the one in Figure 14.1.

Figure 14.1 Corroded Mounting Bracket

Failure to clean the highlighted surfaces will cause nothing but problems. When cleaning, make sure only to remove the corrosion and not to remove good metal. The bracket in Figure 14.2 has had a number of the surfaces damaged by too aggressive of cleaning using an angle grinder. This can allow too loose of a fit for the pads or cause other related problems.

Figure 14.2 Damaged Mounting Bracket

A commonly missed surface, especially where rust is common, are the caliper “ears” that support the outboard pad. These flat surfaces can have considerable rust buildup over time as shown in Figure 14.3. Another source of buildup can come from the use of some of the brake quiet products on the market. If there are remnants of these products on the caliper‘s mating surface it will reduce the surface contact and could increase the chances for brake noise. Failure to clean these surfaces will not allow the outboard pad to sit squarely against the caliper increasing the chances for vibration.

Figure 14.3 Corroded Ears

Once all surfaces have been cleaned they need to be lubed. There are many choices out there for brake lube and as many opinions of which ones to use. I recommend the use of a high quality moly-lube on all metal to metal surfaces and a high quality silicone lube on all metal to rubber parts. The reason I like the silicone on metal to rubber is that silicone repels moisture and if used properly it will form a nice moisture barrier. There are some basic rules of thumb to follow when using both lubricants. One is – “a little goes a long way” or conversely – “too much is not always a good thing”. For example, the bracket in Figure 14.4 should first have a light film of moly-lube applied as shown. Next, install the anti-rattle hardware and apply a thin film to the surfaces that contact the brake pads as in Figure 14.5. The bracket can now be installed on the vehicle.

Figure 14.4 Lubed Mounting Bracket

Figure 14.5 Lubed Mounting Clips

How about the brake pads? What if anything should be applied to the back of the pads? There are a number of different products available for this task so which one should you use? Again, most experts agree that a thin film of moly-lube is the best method to combat brake noise. The key here is to apply it where it will make a difference. Rather than apply it to the entire back of each pad try this, apply a thin layer to each caliper “ear” and then a small circle on the inboard pad where the piston contacts the pad as shown in Figure 14.6. What about pads that already have shims? Should anything be done to them? I say yes, do the same thing. On vehicles with multilayered shims put a thin layer between each layer. If you ever noticed this is how most of these vehicles come from the factory.

Figure 14.6 Lubed Brake Pads

Keep coming back to our blog to get more Tech Tricks Tuesday info and you can read our previous Blog Posts to help solve those brake system problems you might be having.

Outboard Pad Wear and/or Brake Pull

Outboard Pad Wear and/or Brake Pull

Problem:

Brake lead or pull and/or outboard premature pad wear on Chevy & GM trucks

Cause:

Insufficient clearance between caliper and steering knuckle (See Figure 13.1). Heat expansion causes caliper to bind in knuckle causing side to side brake imbalance. This condition will also prevent proper outboard pad release and will result in premature outboard pad wear.

Figure 13.1 GM Caliper Clearance

Solution:

If one of these trucks presents itself with the symptom of brake lead or pull and/or premature outboard pad wear the caliper to knuckle clearance should be checked. Follow the steps below:

1. Measure the clearance individually and add the two values together. Total clearance should be greater than .010”. If clearances are not within tolerances go to next step.

2. Correct clearances by filing metal off of knuckle stops to achieve a total clearance between .010” and .024” (See Figure 13.2). Do NOT remove material from the caliper.

Figure 13.2 Checking GM Caliper Clearance

As always, check out our recent Tech Trick Tuesday Blog Posts.

Stoplight Switch Adjustment & Pad Wear

Stoplight Switch Adjustment & Pad Wear

Problem:

Premature pad wear ranging from mild to severe.

Cause:

While there are many causes of premature pad wear (see our previous Blog posts on this), stoplight switch adjustment can be a common one. It is common enough to have been included in several TSB’s written over the years.

Incorrect stoplight switch adjustment can prevent the brake pedal from returning to a point that allows the cup seals in the master cylinder to open the vent ports as shown in Figure 12.1.

Figure 12.1 Vent Ports

The vent ports allow for fluid expansion when the brakes get hot. If they are not open a residual pressure will be created due to the expanding fluid. The residual pressure will cause the calipers to apply the brake pads slightly and will result in premature pad wear.

Solution:

Vehicles with adjustable stoplight switches will use one of two varieties, adjustable body type or self-ratcheting plunger type. Each is covered below:

Adjustable body type

1. Verify complaint – if there is drag on both front wheels (or all four wheels on 4-wheel disc brake systems) start by loosening the master cylinder away from the vacuum booster by at least .”. This step checks for anything in front of the master cylinder that would be preventing the master cylinder pistons from fully releasing.

2. If the wheels release the stoplight switch adjustment should be checked. Either follow the manufacturer’s procedures or continue with the next step.

3. Duplicate the wheel drag and then loosen the locknut on the stoplight switch. (Figure 12.2)

Figure 12.2 Locknut Style

4. Back the locknuts off to move the stoplight switch away from the brake pedal. Check the brake drag. If wheels released then stop light switch was source of problem. If wheels did not release see page 96 for more information.

5. Adjust the switch by using the locknuts to position it to a point where the plunger is depressed (verify by checking if brake lights are off) making sure pressure is not being applied to brake pedal that would prevent release. (Figure 12.3)

Figure 12.3 Properly Adjusted Switch

Ratcheting Plunger Type (Figure 12.4)

Figure 12.4 Ratchet Style

1. Verify complaint – if there is drag on both front wheels (or all four wheels on 4-wheel disc brake systems) start by loosening the master cylinder away from the vacuum booster by at least. This step checks for anything in front of the master cylinder that would be preventing the master cylinder pistons from fully releasing.

2. If the wheels release, the stoplight switch adjustment should be checked. Either follow the manufacturer’s procedures or continue with the next step.

3. Remove stoplight switch from mounting bracket. This usually involves rotating it 90 degrees in one direction or the other.

4. Pull the plunger out to its full length. (Figure 12.5)

Figure 12.5 Ratchet Style Extended Plunger

5. Insert the stoplight switch back into its bracket while holding the brake pedal in the full released position.

6. Verify proper operation of brake lights.

NOTE: There are other variations of switch adjustments used so it may be necessary to consult the service manual. Always verify proper brake light operation.

NOTE: Cruise control switches can also be the source of the same problem on certain vehicles.

How to Diagnose Side to Side Premature Pad Wear on FWD Vehicles

How to Diagnose Side to Side Premature Pad Wear on FWD Vehicles

Problem:

Inner and outer brake pads on one side wearing out much faster than brake pads on opposite side.

Cause:

The list of possible causes for this pad wear condition is much longer than what most technicians think. Approaching this problem with an incomplete list will result in fixing the symptom not the problem in many cases. The list of possible causes include:

  • Sticking caliper piston on side with problem
  • Check valve brake hose on side with problem
  • Restriction in ABS modulator preventing fluid release on circuit with wear problem
  • Plugged or restricted vent port on circuit with wear problem
  • Opposite side brake hose with restriction
  • Air in opposite hydraulic circuit from problem (i.e. left pads wearing, air is in RF/LR circuit)

    Diagonal Imbalance Fig 11.1

Solution:

Accurate diagnosis of this problem involves 2 components. The first is approaching the problem with a complete list. The second is applying a logical approach to the diagnosis. The first component is listed above. The second component involves the following steps:

  1. Check brake pedal height. Judge pedal against similar vehicles. If pedal has excessive travel or feels spongy bleed and flush entire system paying close attention to the circuit opposite the side with the pad wear.
  2. Test drive vehicle to bring brakes to operating temperature. Raise the vehicle on a lift and check for wheel drag on all four wheels paying close attention to the side where the pad wear is taking place.
    NOTE: If the vehicle cannot be driven due to metal to metal wear the system will have to be restored to a functioning state before complete diagnosis can take place.
  3. If vehicle pulled to side with problem during test drive opposite side brake hose may be restricted. If no other causes of the pull can be determined then brake hose replacement should be suggested.
    NOTE: Many FWD vehicles will NOT pull with a side to side brake imbalance due to what is known as negative scrub radius (See Figure 11.2).  If the vehicle does NOT pull, it does not guarantee the opposite side hose is not restricted. If pressure gauges or clamping plate gauges are available, they should be used to determine side to side braking balance. If not available, a good practice is to perform all other repairs and instruct customer to return in the miles it took to wear the brake pads out for a checkup. Inform them that the opposite brake hose may still be an issue and this step will determine if it is necessary.

Negative Scrub Fig 11.2

Visit us next week as we discuss stoplight switch adjustment and pad wear. If you have missed any of our other Tech Trick Tuesday Blog Posts, you can read about them on our 101 Brake System Tips page.

Policy on Premature Pad Wear

Policy on Premature Pad Wear

Problem:

Customer leaves shop thinking problem is fixed when it is not and returns when brakes are metal to metal.

Cause:

Not taking the steps to insure cause of premature pad wear is actually fixed.

Solution:

Often times the cause of the premature pad wear is obvious and no additional steps should be needed. If the cause is less than obvious or there is any question about whether the repairs that were performed actually will correct the problem, then follow the steps below.

  1. Research how many miles and how long it took to cause the premature pad wear. Take this time and mileage and divide it by 2.
  2. Explain to the customer you would like them to bring the vehicle back for a quick check in the half mileage calculated in step number 1. For example, if the left side pads are wearing out in 5,000 miles, have the customer stop back at 2,500.
  3. After customer leaves, put a reminder to call the customer in your appointment book on the date that represents the time it took the wear to take place.
  4. If the customer doesn’t return by the date in the appointment book, give them a reminder call about the checkup.

Bonus Tip: Using this technique may save you having to replace rotors free of charge.

How to Diagnose Premature Even and Taper Pad Wear

How to Diagnose Premature Even and Taper Pad Wear

We are continuing our discussion on premature pad wear. This week we will be discussing even and taper pad wear. We have discussed several variations of pad wear and this blog post will be the last topic to discuss.

Problem:

One or more brake pads are wearing prematurely or irregularly

Cause:

All pads wearing evenly but prematurely can be caused by the front brakes being overworked due a rear brake problem or front caliper problems or a seized metering valve.

Premature wear of the outboard pad is caused when the outboard pad is not allowed to release off of the rotor properly after the brake pedal is released.

Solution:

Use the following images to help diagnose the cause of the pad wear condition.

Even Pad Wear (All pads worn evenly)

A. Accelerated pad wear (mild)

  • Change in vehicle use from previous set of pads
  • Front to rear brake balance not correct (i.e. rear brake(s) out of adjustment, restricted rear brake hose)
  • Metering valve stuck on open position (Only applies to RWD’s equipped with metering valves)
  • Calipers not allowing proper release of pads due to internal corrosion, seal rollback
  • Inferior friction or friction not suited to vehicle use

Change in Vehicle use from Previous Set of Pads

Front to Rear Brake Balance not correct (i.e. rear brake(s) out of adjustment, restricted rear brake hose)

Metering Valve Stuck in Open Position (Only applies to RWD’s equipped with metering valves)

Calipers not Allowing Proper Release of Pads due to Internal Corrosion, High Mileage OE Calipers, Inefficient Seal Rollback

Inferior Friction or friction not suited to vehicle use

B. Accelerated pad wear (severe)

  • Two foot driving
  • Vehicle being used for commercial application (i.e. delivery, taxi)
  • Venting not being allowed due to plugged or covered vent port in master cylinder

Two foot driving

Vehicle Being used for Commercial Application (i.e. delivery, taxi)

Venting not being Allowed due to Plugged Vent Port in Master Cylinder

Venting not being Allowed due to Covered Vent Port in Master Cylinder

 

Taper Pad Wear

Top to Bottom Taper Wear

Floating/sliding

  • End of pad experiencing wear is binding in bracket or knuckle (can‘t release)
  • End of pad opposite the wear is seized in bracket or knuckle (can‘t apply)

Fixed

  • End of pad experiencing wear is binding in caliper housing
  • End of pad experiencing wear caliper piston not releasing (4 piston caliper)
  • End of pad opposite the wear cannot apply due to seized caliper piston (4 piston caliper)
  • End of pad opposite the wear cannot apply due to pad seized in housing

Inside to Outside Taper Wear

Floating/sliding

  • Brake pad is binding on worn end and can‘t release
  • Brake pad is binding on non-worn end and can‘t apply evenly
  • Rear disc pad with piston locating tab – tab not aligned with piston notch

Fixed

  • End of pad experiencing wear is binding in caliper housing
  • End of pad experiencing wear caliper piston not releasing (4 piston caliper)

Rusting of Caliper Housing Casting Hole

End of pad experiencing wear is binding in bracket or knuckle (can‘t release)

Rear disc pad with piston locating tab – tab not aligned with piston notch

End of pad experiencing wear caliper piston not releasing (4 piston caliper)

This is the final blog post on premature pad wear. We hope that these posts have been informative for you. If you would like to send us feedback on our posts, please visit our Contact Us page and send us a message from there. Next week, we will be discussing a possible policy you should have on premature pad wear and how to help inform your customers so they are happy and safe.

How to Diagnose Premature Pad Wear on RWD and FWD

How to Diagnose Premature Pad Wear on RWD and FWD

We are continuing our discussion on premature pad wear. This week we will be discussing pad wear on rear wheel drive and front wheel drive vehicles. Here is a link to our post from last week on premature inboard pad wear.

Problem:

One or more brake pads are wearing prematurely or irregularly

Cause:

The cause of the pad wear will be based on what type of pad wear is taking place and the configuration of the brake system.

Premature wear of the outboard pad is caused when the outboard pad is not allowed to release off of the rotor properly after the brake pedal is released.

Solution:

Use the following images to help diagnose the cause of the pad wear condition.

  • Front to Rear Split Hydraulic System

    • Piston sticking (symptom – drag)
    • Brake hose on side with problem with check valve condition (symptom – drag)
    • Brake hose opposite side with problem restricted (symptom – pull to side with pad wear)
    • Hydraulic restriction higher than brake hose on side with pad wear not allowing release of pressure (i.e. ABS modulator)

Images for Front to Rear Split Hydraulic Systems (RWD)

9_both_sticking piston_rgb

Piston Sticking (symptom – drag)

9_both_check valve hose_rgb

Brake Hose on Side with Problem with Check Valve Condition (symptom – drag)

9_both_restricted hose_rgb

Brake Hose Opposite Side with Problem Restricted (symptom – pull to side with pad wear)

9_both_abs modulator_rgb

Hydraulic Restriction Higher than Brake Hose on side with Pad Wear not Allowing Release of Pressure (i.e. ABS modulator)

  • Diagonal Split Hydraulic System (All items listed above for Front to Rear Split Hydraulic Systems plus the images below)

    • Piston sticking (symptom – drag)
    • Brake hose on side with problem with check valve condition (symptom – drag)
    • Brake hose opposite side with problem restricted (symptom – pull to side with pad wear)
    • Hydraulic restriction higher than brake hose on side with pad wear not allowing release of pressure (i.e. ABS modulator)
    • Air in opposite hydraulic circuit than side with wear

Images of Diagonal Split Hydraulic Systems (FWD)

9_both_airmc_rgb

Air in Opposite Hydraulic Circuit than Side with Wear (i.e. LF inner and outer pads worn, air in RF/LR circuit)

9_both_vent_rgb

Vent Port Plugged or Covered on Hydraulic Circuit with Pad Wear

How to Diagnose Premature Inboard Pad Wear

How to Diagnose Premature Inboard Pad Wear

The problem, cause, and solution are the same as with outboard pad wear and they are mentioned again here so you do not have to find them in our previous blog posts. We will be discussing premature inboard pad wear this week.

Problem: 

One or more brake pads are wearing prematurely or irregularly

Cause: 

The cause of the pad wear will be based on what type of pad wear is taking place and the configuration of the brake system.

Solution:

Use the following charts to help diagnose the cause of the pad wear condition.

Premature wear of the inboard pad is caused when the inboard pad is not allowed to release off of the rotor properly after the brake pedal is released.

  • Floating/Sliding
    • Caliper housing seized on slide pins
    • Inboard pad binding in bracket due to corrosion
    • Inboard pad binding on slide rails due to corrosion or slide rail wear
    • Caliper piston not releasing properly
  • Fixed
    • Inboard piston(s) not releasing (mechanical)
    • Inboard pad binding on pins or in housing

Floating Caliper Causes

Caliper Housing Seized

Caliper Housing Seized on Slide Pins

Inboard Pad Binding

Inboard Pad Binding in Bracket due to Corrosion

Inboard Pad Binding 2

Inboard Pad Binding on Slide Rails due to Corrosion or Slide Rail Wear

Caliper piston not releasing properly

Caliper piston not releasing properly

Sliding Caliper Causes

Caliper housing seized corrosion

Caliper housing seized due to Corrosion of Caliper Hardware

Inboard pad binding in knuckle

Inboard pad binding in knuckle due to corrosion

Caliper piston

Caliper piston not releasing properly

Fixed Caliper Causes

Inboard piston not releasing

Inboard piston not releasing (mechanical)

Inboard pad binding on pins

Inboard pad binding on pins in Housing

Remember that seized slides or a sticking inboard brake pad should be checked before thinking about a sticking caliper piston.

We will continue diagnosing premature pad wear next week and will get into front to rear split hydraulic systems on both rear wheel drive and front wheel drive vehicles. We may even cover severe and mild accelerated wear and taper pad wear.

How to Diagnose Premature Outboard Pad Wear

How to Diagnose Premature Outboard Pad Wear

Problem:

One or more brake pads are wearing prematurely or irregularly

Cause:

The cause of the pad wear will be based on what type of pad wear is taking place and the configuration of the brake system.

Solution:

Use the following charts to help diagnose the cause of the pad wear condition. We will be discussing Outboard Pad Wear.

Outboard Pad Wear

Description: Premature wear of the outboard pad is caused when the outboard pad is not allowed to release off of the rotor properly after the brake pedal is released.

  • A. Floating caliper
    • Rusting of casting hole – reduces diameter
    • Corrosion of slide pin
    • Lack of lubrication
    • Incorrect lubrication
    • Caliper housing binding in knuckle (insufficient clearance)
    • Pad binding in bracket due to corrosion
    • Pad binding on slide rails due to corrosion or slide rail wear
  • B. Sliding caliper
    • Corrosion of sliding hardware
    • Incorrect lubrication
    • Corrosion of caliper housing/steering knuckle
  • C. Fixed caliper
    • Outboard piston(s) not releasing (mechanical)
    • Outboard pad binding on pins or in housing
7_1_both brake pads one side

Outboard Pad Wear

Floating Caliper Causes

Rusting of Caliper Housing Casting Hole

Rusting of Caliper Housing Casting Hole

Corrosion of Slide Pin

Corrosion of Slide Pin

 

 

 

 

 

 

 

Outboard Pad Binding in Bracket due to Corrosion

Outboard Pad Binding in Bracket due to Corrosion

Outboard Pad Binding on Slide due to Corrosion or Wear of Slide Rails

Outboard Pad Binding on Slide due to Corrosion or Wear of Slide Rails

 

 

 

 

 

 

 

Incorrect Lubrication

Incorrect Lubrication

Lack of Lubrication

Lack of Lubrication

 

 

 

 

 

 

 

Caliper Housing Binding

Caliper Housing Binding

 

 

 

 

 

 

 

Sliding Caliper Causes

Corrosion of Sliding Hardware

Corrosion of Sliding Hardware

Corrosion of Caliper housing:Steering Knuckle

Corrosion of Caliper housing:Steering Knuckle

 

Incorrect Lubrication on Metal to Rubber Parts

Incorrect Lubrication on Metal to Rubber Parts

Fixed Caliper Causes

Outboard Piston(s) not Releasing

Outboard Piston(s) not Releasing

Outboard Pad Binding on Pins or in Housing

Outboard Pad Binding on Pins or in Housing

 

 

 

 

 

 

 

Next week we will continue our post on pad wear and will be discussing Inboard Pad Wear.

How To Do A Quality Brake Job

How To Do A Quality Brake Job

Problem:

Brake comebacks

Cause:

Shortcuts and poor workmanship

Solution:

Most brake comebacks result from not paying attention to detail when performing the brake job. Taking a few extra minutes when performing the service will eliminate the vast majority of comebacks from ever happening. It sort of follows the old saying “pay me now or pay me later”. The difference is paying now involves only a few extra minutes per job and paying me later involves a few extra hours. Here are the steps to take during a brake job:

1. Where possible open the bleeder when retracting caliper piston. The brake hose can also be line locked as an extra precaution (use only approved line locks). These steps will prevent back flushing dirty fluid through the system. If it is not possible to open the bleeder screw, push the caliper piston in slowly to prevent building back pressure. Taking approximately 60 seconds to push the piston back in will reduce the back flush pressure generated to a safe level. When using this step it will be necessary to drain some fluid from the master cylinder reservoir. Either step will reduce the chances of potential damage to the ABS modulator, brake valving or master cylinder.

2. Check all hardware and replace as needed. Weak or worn hardware is a leading cause of uneven and premature pad wear. Restoring the hardware to proper working condition will help to ensure even pad wear and longer pad life.

3. Clean and lubricate all contact points. Metal to metal contact points should be lubed with Moly Lube. Only a small amount is needed to do the job correctly. Metal to rubber parts should be lubed with a high quality silicone lube. The silicone will not damage the rubber parts and helps to form a moisture barrier.

CRC-Dry-Moly-Lubricant

Lube

4. If resurfacing the rotor(s) use proper machining techniques and make sure the lathe is in good working condition. On hubless rotors make sure to clean the mating surfaces with an appropriate tool. Scratch cut all rotors to ensure accurate setup. Always use sharp bits and a vibration damper when machining. After machining apply a non-directional finish using 120 grit drywall sandpaper on a rubber sanding block for 60 seconds per side.

5. Clean the rotor before installing on vehicle to prevent machining dust from contaminating brake pads. The best method to accomplish this is to use a mild soap and water solution. Wash both friction surfaces and wipe dry with a clean lint free rag or paper towels. If using brake clean, use a little more than usual and wipe the surface with a clean lint free rag or paper towels while it is still wet. NEVER use petroleum based cleaners because they leave a residue.

6. Before installing hubless rotors, clean the hub mating surface using an appropriate tool(s). Failure to properly clean this surface can prevent achieving the proper installed runout.

7. When installing new or machined hubless rotors the installed runout should be checked. Using spacers on the studs tighten all lugs to the proper torque using the correct sequence. If runout is not less than manufacturer’s specification index the rotor on the hub to achieve the lowest amount of lateral runout. Before indexing mark the high spot on the rotor and hub. Indexing involves removing the rotor and rotating it one or two lugs and reinstalling. Repeat this until the installed runout is below specification. If runout is out of specifications and does not change as the rotor is rotated check to see if the high spot moves with the rotor or stays with the hub. Failure to install the rotor with installed runout less than manufacturer’s specification is the leading cause of reoccurring pulsation comebacks.

8. Properly torque the wheel lugs using either a hand torque wrench or torque stick sockets. When torquing wheels use a step torque process. To step torque the lugs tighten all lugs to half the normal torque using proper sequence and then fully torque lugs using same process. Make sure your impact has been calibrated before using torque sticks.

9. Test drive the vehicle to ensure proper operation and to break the new friction in. To break the friction in make 10 to 20 stops from 30 M.P.H. down to about 10 M.P.H.. Allow about 30 seconds in between each stop for cooling. This process will properly mate the new pads to the rotor surface.

Hand car keys to customer

10. Deliver the vehicle and instruct the customer for the first 200 miles they should try and avoid panic stops and not to tow or haul heavy loads.

Following these steps each time will reduce, if not eliminate comebacks.

Diagnostic Technique – Symptoms versus Problems

Diagnostic Technique – Symptoms versus Problems

Problem:

Applying a “parts changing” approach to fixing a brake problem.

Cause:

Not using the correct diagnostic techniques to pinpoint the actual cause of the problem.

Solution:

Most problems being diagnosed will have more than one possible cause. The use of the process outlined on page 6 will be the first step in successful diagnosis. Once the list of possible causes has been established the next step in the process involves finding which one is at fault.

An effective technique to determine which of the possible causes is the actual one is to use the symptoms associated with each possible cause to either move it up the list or down the list. Most conditions have related symptoms. These symptoms are an effective tool when used properly.

The best way to demonstrate this is through the use of an example. The example we will use involves a RWD vehicle experiencing fast pad wear on one side not the other. Both inner and out brake pads on one side are wearing much faster than the pads on the opposite side as shown in

Both brake pads one side

Using the diagnostic approach outlined on page 6 we would end up with the following list of possible causes:

  • Sticking caliper piston on side with pad wear problem
  • Check valve brake hose on side with pad wear problem
  • ABS modulator not allowing fluid release on side with pad wear problem
  • Restricted brake hose on side opposite the side with the pad wear problem
  • Hydraulic restriction higher than brake hose on side opposite side with pad wear problem

If we take the same list and add the symptoms each condition would generate we have the following:

#

Condition

Symptom

1

Sticking caliper piston on side with pad wear problem

Wheel drag

2

Check brake hose on side with pad wear problem

Wheel drag

3

ABS modulator not allowing fluid release on side with pad wear problem

Wheel drag

4

Restricted brake hose on side opposite the side with the pad wear problem

Pull to side with pad wear

5

Hydraulic restriction higher than brake hose on side opposite side with pad wear problem

Pull to side with pad wear pattern

Armed with the list above, the first step in any diagnosis would be a test drive. A test drive would allow for a check for a pull and make sure the brakes are at operating temperature. This could be important in duplicating the drag associated with items number 2 & 3.

TIP

Using the technique of looking for supporting symptoms is one of the most effective diagnostic techniques available.

Generic Diagnostic Approach

Generic Diagnostic Approach

Problem:

Misdiagnosis of problem resulting in comeback. Comebacks are not only a nuisance but can be a major problem if you have too many.

Cause:

Not following a structured approach to the diagnosis of the complaint is one of the causes of comebacks that we will discuss today.

Solution:

Apply a consistent effective approach to the diagnosis of all brake problems. The following approach will result in the accurate diagnosis of all brake problems:

  1. Think about the system
  2. Think about how it operates
  3. Think about the problem
  4. Generate a list of possible causes
  5. Diagnose and inspect in a logical manner

Thinking man image

To effectively apply the above steps, it is important to have an understanding of what they involve and where the common mistakes are made. Here is a brief explanation of each:

  1. Think about the system:  All brake systems are not the same and treating them the same can lead to misdiagnosis. The many different brake system configurations make it necessary to identify which type of system you are working on BEFORE entering the diagnostic stage.
  2. Think about how it operates:  This step takes the information from step 1 and applies it to the system’s operation. Because of the many different system configurations there is a wide variance in how the systems operate. This step should answers questions like:
  3. Think about the problem:  This should only be done after applying steps 1 & 2. An important part of this step is in the ability to separate a condition from a symptom. The customer may describe their “problem” as a pulsating pedal. The pedal pulsation is a symptom of something else wrong in the system. Some possible questions to ask yourself might be:

    • What is the expected front to rear braking bias of the vehicle?

    • What kinds of brake valve(s) is the system equipped with?

    • What will effect pedal height?

    • What will turn the red brake light on?

    • When do the rear brakes self adjust?

    • What will cause premature pad wear?

  4. Generate a list of possible causes:  Most problems being diagnosed will have more than one possible cause. Two common mistakes at this stage are approaching the problem with an incomplete list or putting items on our list that can’t cause the problem being diagnosed. An example of this would be adding the master cylinder to our list for a low brake pedal. Conventional master cylinders cannot cause a low brake pedal.
  5. Diagnose and inspect in a logical manner:  If steps 1 to 4 are done correctly this step should be simple. Steps 1 to 4 would allow you to generate a flowchart that will let you to pinpoint which item(s) from the list generated in step 4 apply to the problem you are diagnosing.

Bonus tip: Use this process religiously and it will work. It won’t work without steps 1 & 2 and they can’t be done without a good understanding of all the parts in the system.

Time – Invest it now or waste it later

Time – Invest it now or waste it later

Problem:

Time is one of those things that you cannot get back once it is gone. This is the same for you as a shop owner or mechanic as it is for your customers.

Cause:

Many times, customers come in and we want to get them in and out as quickly as possible. This means that mistakes can happen and you need to be aware of this. The cause is because many times we take the wrong perspective on the issue of time.

Solution:

Time is perhaps the most valuable commodity we have yet we don’t always do everything in our power to use it wisely. Most of what I teach involves investing some additional time up front before any payback can be realized. When presenting ways technicians and shops can make more profit from the brake jobs they are currently performing while at the same time reduce comebacks one of the most common responses I get is “That all sounds great BUT I don’t have the time”. Much of the time I spent coming up through the ranks was spent in busy shops. I know the demands this type of environment puts on everyone involved. I also know what happens when too many corners get cut in the name of getting one more car in. Getting that one extra ticket in may seem like the top priority but how much did it cost to accomplish it?

Balancing the demands of high volume and quality work is not an easy task whether you are the technician putting the work out or the person managing the work flow. We have all heard the saying “Nothing good in life is ever easy”. It is no different in this scenario. Accomplishing both goals in a consistent manner is what truly sets the TOP shops apart from the rest of the pack.

The brake inspection process is often shortchanged in an effort to maximize work flow. Common short cuts taken include no pretest drive, no underhood check, pulling only 2 or 3 wheels and never pulling the calipers. The perception is that by taking these and other shortcuts it is helping the shop’s busy volume. What is not considered is the “dead” bay time the comebacks caused by these shortcuts cost the technician and the shop or the loss of credibility that takes place each time a customer has to come back. The few extra minutes it would take to turn an incomplete inspection into a complete one will pay big dividends including more legitimate profit per job and less unproductive bay time. Here are some real life examples of how shortcuts cost money.

Seized wheel cylinder

1.1 Seized wheel cylinder

Figure 1.1 shows what a shop found when they went to bleed a system out after selling $600 worth of wheel based brake work. They never opened the hood until after the work was completed. The system had been contaminated with power steering fluid and required $800 in additional work. You or I wouldn’t want to be in the manager’s shoes who had to tell the customer would we? We have to ask ourselves was the time this shop saved in not performing an underhood inspection on each car worth it?

Swollen Diaphragm

1.2 Swollen Diaphragm

Figure 1.2 shows one of two seized wheel cylinders found on the third visit. The reason for each visit was warranty of the loaded calipers installed. The front brake pads on the vehicle were only lasting 2,000 miles. On the third set of warranty calipers, the shop finally took the time to check if the wheel cylinder pistons were actually moving – guess what they weren’t. This vehicle should be braking with a 60/40 front to rear split but because of the seized wheel cylinders it had zero rear braking. The braking balance on this vehicle was 100/0!

Missed Conditions

1.3 Missed Conditions

Premature pad wear, over heating, drag and brake noise can all be related to proper caliper function but how many shops check the function of the caliper during the inspection? Very few shops I see in the field ever take time to pull a caliper during the inspection. Not pulling the caliper can lead to missing both pad and caliper related conditions. Figure 1.3 shows some of what can be missed by NOT pulling the caliper.

Failure to pull some calipers will cost the shop the brake job in some  cases. The friction and caliper will look good on the outside but have hidden problems. The shop will give them a clean bill of health and miss the sale OR it could cost after the job is sold. If the shop sells based on the outside inspection and then finds other needs after the job is started it can get pretty ugly going back to the customer with additional costs.

A good technician should be able to perform a complete 4-wheel inspection on a typical vehicle in 15 to 25 minutes without missing anything. This is about 10 minutes more than what is being spent currently in most shops. That extra 10 minutes will work for you or against you depending on how you use it. The additional time spent to do a thorough inspection, should yield happier and safer customers because you are going to find things you may not have found otherwise.

Keep coming back for our Tech Trick Tuesdays and keep learning about tips and tricks that can change the way you do business and the way your customers see you.

Wasting Time Solving a Problem?

Wasting Time Solving a Problem?

Problem:

Have you ever wasted hours trying to solve a problem only to find that there has been a solution to that problem the entire time? I have and it can be extremely frustrating.

Cause:

Not checking for existing Technical Service Bulletins (TSB’s) or other resources before attempting a service repair can be a major point of frustration.

frustrated mechanic

Solution:

Manufacturers constantly publish Technical Service Bulletins (TSBs) that explain a problem and its solution. There are thousands of TSBs on brakes alone. The days of being able to pull everything from memory are long gone. A techncian’s reliance on the written or electronic word increases everyday. Accessing this information should be incorporated into the service process. The process should proceed as follows:

  1. Customer interview (See page 2 for more detail)
  2. Check vehicle for existing TSBs
  3. Test drive
  4. Inspect & diagnose
  5. Perform repairs

Incorporating the check for TSBs at this stage in the process will allow you to include any road test tips the TSB may provide in your test drive. Some TSBs provide information on how best to duplicate a problem and what to look for during a test drive.

Many shops wait until they are in trouble before checking for TSBs. This is a mistake. The sooner you have the information the better off you will be. Many of the fixes listed in the TSBs will never be able to be duplicated in the field regardless of the amount of time and effort put forth. Having the information before you perform your diagnosis will save time and effort. With so much information available and access to this information being made easier every day, why not use it to same time, headaches and frustration? We hope you will and we hope you keep coming back for more Tech Trick Tuesday tips and tricks.

Parts Changer versus Brake Technician

Parts Changer versus Brake Technician

Problem:

What happens when you diagnose a problem by trying to throw parts at it to fix it instead of diagnosing it correctly? Does this happen in your shop with some of your technicians? What is your customer’s reaction to this problem?

Cause:

The majority of people servicing brakes have obtained most of their knowledge on the job. While hands on experience is sometimes the best teacher, it cannot always provide the knowledge that is necessary to understand the inner workings of the various brake parts and systems. Without this understanding, accurate diagnosis can be extremely difficult if not impossible.

Auto-Parts

Solution:

In the eyes of most technicians and consumers, the brake system is relatively simple. Disc brakes in the front and drum or disc brakes in the rear. “Throw” a set of pads on it and it will be fine. This oversimplification of the brake system leads to many of the problems that are encountered. The brake system is a complex system. It has many components which are dependent upon one another to function properly. The key word is “system”. They work together to stop the vehicle. When one part of the system is not working properly, then other parts of the system will be affected. There is a direct relationship between how good a technician is and how much they know about how each part in the system works. Correct and accurate brake system diagnosis depends on having a clear understanding of:

  • how each part works…
  • what can go wrong with it….
  • and what that will cause.

Many technicians servicing brake systems do not have a good enough handle on the first point listed above, how each part works. Without this the technicians will be faced with replacing parts to try and correct a problem. This is the definition of a “parts changer”. Brake technicians have a clear understanding of each part in the system and how it relates to the overall system operation. This gives them the ability to understand what can go wrong with the part and what it will cause. They use this in applying a logical approach to the diagnosis of the various brake problems they encounter.

Technicians must constantly seek out new sources of information. These tips and blog posts are examples of where to get the kind of information necessary to allow accurate diagnosis of many different brake problems. Other resources include trade publications, seminars, webinars, and the internet (many resources here with YouTube, Facebook, Automotive Forums, etc…). With the constant advancement of vehicle technology, the learning process will never be over. We hope that you will keep coming back for our Tech Trick Tuesday Blog Posts.

How to perform a proper brake job customer interview

How to perform a proper brake job customer interview

Problem:

What happens when you do not fix the customer’s complaint and how does that happen? We will be discussing the problem of not fixing the customer’s complaint, the cause, and the solution so that you are able to be that shop that all the customers like to go to and that they refer their friends and family to.

Cause:

The cause of not fixing the customer’s complaint is that you may not know what that complaint is because there was a breakdown in the communication or understanding between you and the customer during the customer interview.

Solution:

customer-satisfaction

The primary goal of the customer interview is to gather enough information to allow the technician to duplicate the customer’s complaint so that the customer knows you are offering great customer service. Asking open-ended questions is an effective method to accomplish this. Following the outline below will usually result in gathering the necessary information:

  1. Ask the customer what their primary complaint is. Log complaint on checklist.
  2. Ask the customer is the problem occurring now? If answer is no then get details of when it does occur
  3. Ask the customer how long has the vehicle had the problem
  4. Ask the customer is the problem getting worse over time
  5. Ask the customer how often they use the parking brake and whether they or anyone has added brake fluid recently
  6. Log any other related information in the comments section of the checklist

Once interview is complete customer should be informed of what is going to take place. Make sure to include the following information:

  • The vehicle will be taken for a test drive
  • We will do a 4 wheel brake inspection
  • How long it will be before we can look at the vehicle
  • How long the inspection process will take

Whenever possible, have the customer drop off the vehicle. This takes the pressure off of everyone involved. If not possible, make sure to add a “cushion” to the times given the customer. If you think it will be 10 minutes before you look at the vehicle, tell the customer 15. This gives you a little breathing room and will allow you to exceed the customer’s expectations more often than not. It is what sales people call “Under promise and over deliver” and most customers appreciate this. The opposite is to “over promise and under deliver” and this generally results in some very upset customers.

If for any reason there is a delay in either getting the vehicle in or during the inspection, make sure to notify the customer as soon as possible to prevent any problems. Apologize to the customer, explain what has happened, and give them the adjusted times. Always remember to perform a thorough customer interview and to under promise and over deliver.

Keep coming back for our Tech Trick Tuesdays and keep learning about tips and tricks that can change the way you do business and the way your customers see you. If you missed last week, you can read about our thoughts on Brake Service Philosophy.

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