> Date: Wed, 13 Jun 2007 02:58:51 -0400
> From: "Rick" <patton@suscom-maine.net>
> Subject: RE: [TR] brake rotor runout
>
> 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/
Check around at various shops in your area, the shop I take my cars to
locally has machine that turns the rotors on the hub of the car. When I
saw this machine in action on my wife's car I asked the owner about it
he said he was really happy with it. He has never had a customer come
back with pulsing brakes with this new machine.
Doug Hamilton
60 TR3A
63 Fiat Cabriolet
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