Vehicles returning with complaints of brake noise
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.
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:
- Pads and rotor
- Pads and caliper
- Caliper and knuckle or mounting bracket
- Pads and knuckle or mounting bracket
- Caliper and mounting hardware
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.
• 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.
• 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.
• 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.