Quote:
Originally Posted by cycleguy55
The runout I'm referring to is normal, and at levels insufficient to be felt in the brake pedal. It's probably the extremely rare brake rotor that has zero runout at any given temperature, and even rarer for zero runout at all temperatures.
For example, here are excerpts from a Factory Service Manual for runout and rotor thickness variations:
Runout limit: 0.035 mm (0.0014 in) or less
Maximum uneven wear (measured at 8 positions): 0.015 mm (0.0006 in)
You'll note the maximum for uneven wear or runout isn't zero. IOW, some runout or rotor thickness variation is acceptable within limits.
While I've found references that would indicate each of us is correct, this would indicate it may be a bit of both: https://auto.howstuffworks.com/auto-...isc-brake2.htm
"the rubber piston seal and any wobble in the rotor may actually pull the pads a small distance away from the rotor" |
Yes, that is all true, but note the max values in this case, about 1.5 thou, etc.
Watch a caliper grab a rotor, and then relax when the pedal is released.
That's the bore seals dragging the pistons back that fraction.
That's without turning a rotor.
I always aim for zero runout on car, and if indexing rotors doesn't achieve within tolerance, then an on-car disc machine is advised.
I've seen many cars come back after some low miles with brake shudder from a previous poor brake repair.
Now back to original topic.
Gary