Shimming rotors
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
This shimming is merely disguising or covering up a problem. It has to be a "do it yourselfer repair" from God only knows where because the correct way is to machine the rotors. They will never be exactly true when re-hubbing the fronts with new rotors. But they will be true on a machine, unless the machines shaft is out of round. As Red 71 stated, preparation and cleaning should be obvious to re-hub as close to zero as possible. Then machine the rotor to zero. The best way to avoid comebacks is too make it right the first time. .
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
This shimming is merely disguising or covering up a problem. It has to be a "do it yourselfer repair" from God only knows where because the correct way is to machine the rotors. They will never be exactly true when re-hubbing the fronts with new rotors. But they will be true on a machine, unless the machines shaft is out of round. As Red 71 stated, preparation and cleaning should be obvious to re-hub as close to zero as possible. Then machine the rotor to zero. The best way to avoid comebacks is too make it right the first time. .
Melting Slicks
Joined: Feb 2003
Posts: 3,053
Likes: 4
St. Jude Donor '03,'11
I agree with you Ironcross, but the fact is the axle shaft and rotor were rough machined first and then finally machined as a unit to true the assembly. If the old rotor, or a new one, is chucked up in a machine and turned, it is true with its own flange, but when bolted together as a unit, there is no guarantee it will be true as an assembly. The only way to achieve this is to do them as a unit, or true up the axle face also. Most of the time the axle is still on the car when brake shops take the rotors off to turn them. I have had to fix a ton of them that were turned by supposedly professional brake shops.
I don't bother to do anything because i use wilwood calipers that don't pump air.
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
Some do, but that's a joke too. With up to .008 clearance and that shaft jumping around, there is no way that thing can be counted on for accuracy. Works fine on modern bearings.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
The only way a rear would be out of round is if the rear bearing housing was crashed and bent or just plain dead. If its that bad he needs a new one anyway Its a perfect situation to be correct. It`s chucked up the same as a hub-less front wheel drive car. And the fronts are done with the bearing races in place. Those machines that do the rotors on the car are just a mistake waiting to happen...I have seen them in operation at trade shows, heavy, costly, and takes forever. Not a very popular tool in brake shops. I recall only one and its still in like new condition in the guys back room. He cant even give it away. 
well, i`m outta here,,,
well, i`m outta here,,,
Thread Starter
Heel & Toe
Joined: Feb 2009
Posts: 22
Likes: 0
Thanks for all the great info. Got to work on it a little this weekend and the runout on the rotor (which is .015) is als on on the spindle flange. It is also been worked on before so it looks like new bearings and a spindle to do the job right. Thanks again for the info.
Melting Slicks
Joined: Jul 2006
Posts: 2,373
Likes: 6
From: Baltimore MD
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Tech Contributor
Joined: Aug 1999
Posts: 15,160
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From: Connecticut, USA
Thanks for all the great info. Got to work on it a little this weekend and the runout on the rotor (which is .015) is als on on the spindle flange. It is also been worked on before so it looks like new bearings and a spindle to do the job right. Thanks again for the info.
I've gone thorugh this before so no need to start an arguement with anyone but corvette rear brakes require either facing the rotor/spindle as one or correctly shimming and bolting the rotor on in a fixed position. I've had new spindles and new rotors go on with under 005 runout or as high as 015". It is much easier and perfectly safe to bolt and shim the rotors. Many shops wrecked rear rotors by facing them off the spindles. The surface was fine just wasn't perpendicular to the axle centerline.
Trying to shim rotors without dressing the mating surfaces and without a full range of shims will not give good results. Done properly they are fine, better then using lug nuts alone to secure the rotor.
To each his own, good luck.