Shimming rotors
Le Mans Master
Joined: Jan 2000
Posts: 8,918
Likes: 27
From: New Hill NC
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
The shim is used to zero the runout on the hub. Most shops would turn down the rotor to set runout. By definition that takes off material from the rotor and puts it out of paralell. The shim corrects the problem with no dammage.
Something else to concider if you haven't already. If the rotor itself is off a bit in addition to the face of the hub being off, you might be able to rotate the rotor on the hub to minimize the runout or possibly eliminate it alltogether. Then just shim as necessary.
Something else to concider if you haven't already. If the rotor itself is off a bit in addition to the face of the hub being off, you might be able to rotate the rotor on the hub to minimize the runout or possibly eliminate it alltogether. Then just shim as necessary.
Last edited by SIXFOOTER; Feb 13, 2009 at 05:33 PM.
Burning Brakes
Joined: Oct 2004
Posts: 801
Likes: 17
From: Middletown Delaware
I have used this a couple times now. Shim a little pricey but fast. Napa sells them. Dave
http://www.brakealign.com/pages/products.htm
http://www.brakealign.com/pages/products.htm
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Pro
Joined: Sep 2002
Posts: 624
Likes: 1
From: Melbourne, Fla. 6 months- New Middletown, Ohio 6 months
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
The best way to true up a rotor is to machine turn them with a 'good' brake lathe. I can cut as little as a thousand on the machines we use. And Vettes are one of the easier rotors to machine. We have litterly cut hundreds of rotors without comebacks. I guess that's why I object to shims. We also re-cut rotors machined by other parts stores that was poorly done. And in reverse this could also be a reason to use shims by customers afraid of a bad job. But used rotors are not always out of round in the same places because of the warpage from heat resulting in a pulsating pedal. You dont have to cut much unless the pad has broken loose from plate on 90% of the rotors. If there too bad, then replace them. Minimum thickness is stamped on the insides. However the way some new rotors are stored can sometimes effect the out of roundness also. And it really dont make any difference between off shore and U.S. made. You should cut them all to make sure there true.
Safety Car
Joined: Aug 2001
Posts: 4,883
Likes: 11
From: North Easton Mass
The best way to true up a rotor is to machine turn them with a 'good' brake lathe. I can cut as little as a thousand on the machines we use. And Vettes are one of the easier rotors to machine. We have litterly cut hundreds of rotors without comebacks. I guess that's why I object to shims. We also re-cut rotors machined by other parts stores that was poorly done. And in reverse this could also be a reason to use shims by customers afraid of a bad job. But used rotors are not always out of round in the same places because of the warpage from heat resulting in a pulsating pedal. You dont have to cut much unless the pad has broken loose from plate on 90% of the rotors. If there too bad, then replace them. Minimum thickness is stamped on the insides. However the way some new rotors are stored can sometimes effect the out of roundness also. And it really dont make any difference between off shore and U.S. made. You should cut them all to make sure there true.
Rick B.
Pabst Blue Ribbon aluminum shim stock works well
Safety Car
Joined: May 2008
Posts: 3,747
Likes: 713
From: Lafayette Louisiana
76 rotor shim job
This confused me too, until I read somewhere GM (I think I got this story correct) riveted the rotors to the hub and then machined the rotor off the hub center line as a assembly.
As info, my 2 front rotors were brand new and and when installed, the runout was off. I could rotate them a bolt hole and the runout would follow the change. So I concluded my rotors was perfect, but the hub was out and the only way to fix runout was to either rivet together and machine rotor as an assembly as GM did or do the shim routine.
On the back, I reused the old rotors after drilling out the rivets to replace the parking brakes. Old rotors were in good shape. I had too much runout on the RR rotor and solved that problem by rotating the rotor to a different bolt hole. Only problem was I had to use a rivet hole to adjust the parking brake instead of the larger intended hole.
Hope this history might help. Any suggestions are welcome too!
As info, my 2 front rotors were brand new and and when installed, the runout was off. I could rotate them a bolt hole and the runout would follow the change. So I concluded my rotors was perfect, but the hub was out and the only way to fix runout was to either rivet together and machine rotor as an assembly as GM did or do the shim routine.
On the back, I reused the old rotors after drilling out the rivets to replace the parking brakes. Old rotors were in good shape. I had too much runout on the RR rotor and solved that problem by rotating the rotor to a different bolt hole. Only problem was I had to use a rivet hole to adjust the parking brake instead of the larger intended hole.
Hope this history might help. Any suggestions are welcome too!
Pro
Joined: Sep 2002
Posts: 624
Likes: 1
From: Melbourne, Fla. 6 months- New Middletown, Ohio 6 months
Ironcross, I agree with you that the bottom line is to do it right. Like everything else, when it comes to selecting a shop to do specialized work it pays to take the time to get references from past customers. If the shop does not want to provide a list of at least 5 or 6 that have had the same service you need, then you need to look elsewhere.
72LS1Vette also mentioned something very important. No matter how good the turn job is, if the hub you are going to mount this rotor on is not cleaned properly you will defeat all the efforts you went through to get the rotors trued. Prep work is always the key to good results. Anyone that has done a lot of automotive work has sooner or later learned the hard way.
72LS1Vette also mentioned something very important. No matter how good the turn job is, if the hub you are going to mount this rotor on is not cleaned properly you will defeat all the efforts you went through to get the rotors trued. Prep work is always the key to good results. Anyone that has done a lot of automotive work has sooner or later learned the hard way.
Le Mans Master
Joined: Apr 2007
Posts: 7,353
Likes: 72
From: Graceland in a Not Correctly Restored Stingray
Shims I used to accomplish ~0.001" runout (sufficient to clear the pads from dragging on the surface when braking pressure is not being applied without being so much as to cause pedal kick) were provided by Dick G. Pretty sure they're stainless. Not sure Guldstrand carries them anymore and don't believe they've ever been cataloged.
Last edited by TheSkunkWorks; Feb 14, 2009 at 12:43 PM.
