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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.

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