RANT: Skipping Measurements on Rotors

brake pulsationYou may think that you are not paid to measure thickness and runout, but are you paid for a comeback?

Even if you install a new rotor, you are setting yourself up for a comeback if you do not measure using a micrometer or dial indicator. Even a “perfect” premium rotor will have runout if it is put on a flange with runout or corrosion.

Installing new rotors is not a way to avoid having to use a micrometer or dial indicator. For every brake job, you should always measure for runout (rotor and flange) and the dimensions of the rotor before brake service is performed.

After the rotor is resurfaced or a new rotor is installed, the rotor should be measured for runout when it is installed on the vehicle as a quality control method. A new rotor could have excessive runout when it is installed on the vehicle due to a stacking of tolerances.

You may think that installing new rotors eliminates the possibility of a comeback. However, this myth creates more comebacks that it solves. These comebacks often start with blaming the new pads, and ends with the customer having to return a second or third time until someone pulls out a dial indicator and micrometer.

Let’s say a vehicle had .003” of lateral runout when measured at the outside face of the rotor. If this vehicle is riding on 205/55R16 tires, in one mile, the high-spot with .003” of runout goes past the caliper approximately 836 times. Over 6,000 miles, that spot on the rotor will go past the pads more than 5 million times. Every time this spot passes the pads, a little bit of the rotor’s material is removed. Over the course of those 5 million revolutions, enough material is removed to create a thickness variation that can be felt by the driver.
This is why it is critical to measure thickness and runout in a brake rotor and wheel flange even if new rotors are going to be installed.
  • Chad

    And if there is runout after a rotor replacement?? What are you suggesting to the customer that came in for a simple brake job??