Rotor Indexing

May 8, 2021

When you run into runout problems, there can be a few different culprits. Because of this, it is important to determine the correct source in order to fix the issue. One of the best ways to do this, is by rotor indexing. By performing an index not only will you find the problem, but often times, you'll fix it as well. Typically, installed runout can be caused by any combination of the following:

Rotor has runout
Hub has runout
Hub to motor mating surface is not clean

This article will go over a process known as "indexing" in order to help you identify and correct any installed runout you may come across.

Rotor to Hub Index

The following steps will go over the indexing process. Following these steps will help you find the issue and, in most cases, fix it as well. To get started, follow the steps below to index the rotor to the hub.

Tip: Using this procedure will either correct the runout problem or tell you whether the problem is related to the hub or rotor

Tip: Using this procedure will either correct the runout problem or tell you whether the problem is related to the hub or rotor

1. Measure rotor runout

2. If runout is greater than the allowable specification (usually no more than .002") then proceed to the next step.

3. Index the rotor to a wheel stud.

4. Rotate rotor until the dial indicator reading is at its highest value. Use a magic marker to mark this point on the rotor and hub flange as shown in the image below:

Rust buildup

5. Next, remove the rotor. Check the hub and rotor mating surface for dislodged rust or anything else that could cause the runout. If the mating surface is good install the rotor by rotating it 2 lug positions from its original position.

6. Finally, Measure the runout. If it is now within the specifications, proceed to the next wheel. If not, rotate the rotor until the dial indicator reading is at its highest value. Continue by checking the position of the marks on the rotor and hub in relation to the high spot. If the high spot aligns with the rotor, the rotor is the source of the runout. If the high spot aligns with the mark on the hub, then the hub has runout.

Indicator Dial

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