Rick and Doug, thanks for the helpful information. The brakes are working
fine at the moment, with no pulsing that I can feel.I think I'll leave well
enough alone for now, but continue to monitor them periodically.
Tom
----- Original Message -----
From: "Rick" <patton@suscom-maine.net>
To: "Tom Note" <tom628@verizon.net>; "TR List" <triumphs@autox.team.net>
Sent: Wednesday, June 13, 2007 2:58 AM
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/
>
> 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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