Tom,
We turn brake rotors at our store and, in general, the typical runout limit
before turning is required is 0.006". And even at that you may not feel any
pulsation in the pedal.
> 2. Could the runout be caused by some irregularity where the rotors
are
> mounted to the hub?
Absolutely. If you buy a new set of rotors and bolt them to the hubs without
cleaning off the rust and dirt they will wobble to some degree. Almost
always a customer returning new rotors, because "they pulse as bad as the
old ones" has not cleaned the hub. Not to say that new rotors are always
perfect but they are cut on very expensive lathes and inspected carefully.
Unless mishandled in shipping there isn't much to go wrong. 3M has just
announced a hub cleaning kit that they expect to be a huge seller.
You can try rotating the rotors on the hub to minimize runout. If your brake
pedal isn't pulsating they are probably OK anyway. And if you have them
turned, you'll need about 0.030" in thickness over the discard figure for
safety. I've cut several thousand rotors and you may not realize it but
brake lathes are only accurate to about 0.002" and that is with a skilled
operator. You can cut a rotor, put it back on the same lathe, and because
of the way rotors mount, have two or three thousandths runout. For super
accurate rotors on high end race cars, we grind them on a flywheel grinder
after cleaning the mounting surface carefully. A little tiny wobble is
actually good as it knocks the caliper pistons back a tad minimizing pad
wear.
Rick Patton
75TR6sci
http://topshamautoparts.com/tr6/
snip
> My questions are:
> 1. Do the above readings require replacement of the rotors?
> 2. Could the runout be caused by some irregularity where the
> rotors are
> mounted to the hub?
> TIA,
> Tom
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