I had a car in for a front/rear brake service yesterday.
On each axle, the car received new premium rotors, premium pads and new hardware. The hub flange was also thoroughly cleaned using a wire wheel.
I measured the lateral runout of each rotor once it was installed. Prior to taking the measurements, the rotors were installed using conical washers and lug nuts that were torqued to the specified 100 ft-lbs.
These were the readings that I obtained:
LF 0.001”
RF 0.0015”
LR 0.002”
RR 0.0005”
Note: on this particular vehicle, the manufacturer allows for up to 0.002” of lateral runout.
For the LR and RF rotors, I removed the rotors and re-mounted them approx. 180-deg from their original position. In both examples, the runout value was significantly reduced; the final reading for the RF was 0.001”, and the LR was less than 0.001”.
My personal opinion is that the less lateral run-out you have, the less likely that you will develop disc thickness variation issues overtime. Disc thickness variation is what causes most pedal pulsation issues. However, I discussed this story with a person offline, and he stated that having a low lateral runout value does not tell the full story.
In his opinion, even if the runout is low when the rotors are at room temperature, it is hard to determine “what happens” once the rotors are hot. In his opinion is that if there is a casting issue, it is impossible for the average technician to confirm this during initial installation. Supposedly, a non-uniform cast can cause the rotors to expand unevenly when they heat up?
I look forward to hearing your thoughts on this matter. Do you feel that measuring rotor runout is a critical part of doing a proper brake job? If not, please share your feedback.
Thanks!
On each axle, the car received new premium rotors, premium pads and new hardware. The hub flange was also thoroughly cleaned using a wire wheel.
I measured the lateral runout of each rotor once it was installed. Prior to taking the measurements, the rotors were installed using conical washers and lug nuts that were torqued to the specified 100 ft-lbs.
These were the readings that I obtained:
LF 0.001”
RF 0.0015”
LR 0.002”
RR 0.0005”
Note: on this particular vehicle, the manufacturer allows for up to 0.002” of lateral runout.
For the LR and RF rotors, I removed the rotors and re-mounted them approx. 180-deg from their original position. In both examples, the runout value was significantly reduced; the final reading for the RF was 0.001”, and the LR was less than 0.001”.
My personal opinion is that the less lateral run-out you have, the less likely that you will develop disc thickness variation issues overtime. Disc thickness variation is what causes most pedal pulsation issues. However, I discussed this story with a person offline, and he stated that having a low lateral runout value does not tell the full story.
In his opinion, even if the runout is low when the rotors are at room temperature, it is hard to determine “what happens” once the rotors are hot. In his opinion is that if there is a casting issue, it is impossible for the average technician to confirm this during initial installation. Supposedly, a non-uniform cast can cause the rotors to expand unevenly when they heat up?
I look forward to hearing your thoughts on this matter. Do you feel that measuring rotor runout is a critical part of doing a proper brake job? If not, please share your feedback.
Thanks!
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