How to Measure Rotor Runout

How to Measure Rotor Runout

The rotor runout dial indicator is used primarily to measure rotor runout. Likewise, it may be used to measure arbor runout on the bench lathe, wheel bearing play, and hub runout. Even so, the tool must be used to correctly in order to get an accurate reading. Because of this, runout measurement is often not performed correctly and yields inaccurate results.As an example, this article will go over the correct steps to completing the process.

How to perform a Rotor Runout Measurement

1. Attach Vise Grips:

To begin, attach the flexible mount to vise grips. As you'll see, there should be three mounting holes in the mounting block. Typically, the end one will be the best option, use it when possible.

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

In order to keep everything stable, be sure to locate a solid mounting point on the vehicle. For example, consider the caliper mounting bracket, pad rails, lower strut mounting bolt, or steering arm. On the other hand, be sure to mount on a stationary location that is not attached to the rotor.

Vice Grips Attached to Bolt

In addition, there must not be any bearing play on hub style rotors. If excessive play is present, adjust the bearing before you measure. On the other hand, hubless rotors have to be secured with spacers and lug nuts. For example, a 5 lug hub should use 3 lug nuts. Likewise, on a 4 lug hub, use 2 opposite lugs with spacers. Likewise, the lug nuts should be installed backwards (when possible) with the flat sides against the spacers.

2. Attach Dial Indicator

To attach the dial indicator, loosen the clamp screw and tighten it to a point that the indicator can move freely. Next, make sure that the red handle points directly in line with the base of the flexible mount. To do this, turn the adjusting screw clockwise. (see below)

Indicator Clamp

3. Set the Plunger

Next, locate the dial indicator plunger as shown below. The tip should be about 1/4" from the edge of the rotor. In addition, the plunger should be placed on a smooth portion of the rotor. If necessary, take the rotor runout reading on the inner surface of the rotor. Likewise, the plunger should extend out of the housing and the contact tip should be at a slight angle in line with the edge of the rotor. (see below)

Close Up of Needle

4. Add Tension to the Rotor Runout

While holding the indication in position, rotate the red tension handle 189 degrees or until there is enough tension to hold the unit stationary.

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

5. Take the Rotor Runout Reading

Finally, the rotor runout reading can be taken. To do this, rotate the rotor in the direction that the dial indicator tip is pointing. Next, watch the needle for the lowest and highest number reached during one revolution. The runout number will be the difference between these two numbers. For example, if the lowest reading was 65 and the highest was 69 the runout is .004" (see below).

Runout reading on dial meter

To use the "zero" feature rotate the rotor until the lowest reading is obtained. Next, loosen the set screw and rotate the black dial until the needle point to zero. Finally, rotate the rotor a complete revolution and note the amount of runout. As a result, 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 rotor runout will be an issue in a vehicle that comes back with pulsation.

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