Spent 2 hrs today doing both rear rotors I got 1 to .002 and the other is at .0025 have to make another shim and check again.
rotor run out
Thread Starter
Instructor
Joined: Dec 2005
Posts: 121
Likes: 2
From: Middletown Delaware
rotor run out
I am checking rotor run out trying to solve a fading brake pedal. Back is +/- .001 and +/- .004, front is is +/- .006 and +/- .003. Couple of questions:
1) I read the spec is +/- .002 is that correct?
2) Should I try to get to a tighter tolerance.
Thanks
1) I read the spec is +/- .002 is that correct?
2) Should I try to get to a tighter tolerance.
Thanks
Melting Slicks
Joined: Apr 2002
Posts: 2,337
Likes: 14
From: Norfolk VA
The General states runout at .005. So one of your rotors are out of specs. However other members such as GTR1999, state one should get run out to .002 to resolve the spongy pedal issue. I replaced all my rotors and replaced the RF and LR calipers, installed speed bleeders, and bled the brake system with a Motive pressure bleeder and the spongy pedal is gone. Some members will say this is a band-aid approach to fixing the spongy pedal problem. Although my spongy pedal is solved, I am converting to the C5 brakes, both front and rear. Because checking rotor runout, shimming rotors, checking runout again can be a pita.
Last edited by Oldguard 7; Jul 9, 2008 at 09:32 PM.
Melting Slicks
Joined: Oct 2002
Posts: 2,865
Likes: 1
From: I may be getting old but I refuse to grow up
Melting Slicks
Joined: Apr 2002
Posts: 2,337
Likes: 14
From: Norfolk VA
checking for for runout .that is such a pita. 2 hours just to change rotors. It shouldn't take 2 hours replace rotors.
I changed rotors on all four corners and replaced the LR and RF calipers as they were leaking. I installed speed bleeders and used the motive brake bleeder to bleed them and my pedal is firm as ever. I did not check for runout. For all the brake problems concerning rotor runout threads I read on the forum, I must have gotten lucky. I am putting C5 brakes on both the front and rear brakes.
I changed rotors on all four corners and replaced the LR and RF calipers as they were leaking. I installed speed bleeders and used the motive brake bleeder to bleed them and my pedal is firm as ever. I did not check for runout. For all the brake problems concerning rotor runout threads I read on the forum, I must have gotten lucky. I am putting C5 brakes on both the front and rear brakes.
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Thread Starter
Instructor
Joined: Dec 2005
Posts: 121
Likes: 2
From: Middletown Delaware
Shim stock will be in tomorrow and I will work on it this weekend. That is a good point about where it is after it has been run for awhile. I just heard about using c-5 breaks. What is the advantage? What does it take?
Melting Slicks
Joined: Apr 2002
Posts: 2,337
Likes: 14
From: Norfolk VA
Opinions vary. The C5 brake system is of a floating caliper design whereas runout occurs but it is not as critical because of the floating caliper design. VBP sells a C5 front brake kit. A few members have done this front brake conversion and have not reported any problems. I am doing both front and rear brakes as I have the necessary components to do so. I am having caliper mounting brackets fabricated for me. I also have C6 wheels because the C5 calipers are wider than the fixed C3 caliper.
Instructor
Joined: Jul 2000
Posts: 239
Likes: 5
From: Rochester NY
Would it not be better to pull the two front hubs and press out the studs, then take the hubs to a machine shop and have the faces turned untill the hub are running true, that would end all future problems when replacing brake rotors........
I would think that brand new rotors are running true and paralell, since almost everting made today is manufactured on a CNC machine.
I would think that brand new rotors are running true and paralell, since almost everting made today is manufactured on a CNC machine.
Safety Car
Joined: Oct 2006
Posts: 3,930
Likes: 15
From: Calgary Alberta
Intermediate
Joined: Jul 2008
Posts: 45
Likes: 0
Any chance someone has pictures of the rotor run out repair process? I think my 73 has it real bad. I've done plenty of brake jobs on other cars, but have never had experience with this run out problem.
What are the shims you use made of?
Where do you measure for this?
On the rear wheels, if you need to spin the rotor to see how it rides in the caliper... I've tried this, but it's really tough to spin the back rotor even with the car in neutral due to the e Brakes....
I really am concerned about this condition on my car... the rear wheels are toed in really bad and I'm blowing through tires on the inside edge.
Thanks,
Roc
What are the shims you use made of?
Where do you measure for this?
On the rear wheels, if you need to spin the rotor to see how it rides in the caliper... I've tried this, but it's really tough to spin the back rotor even with the car in neutral due to the e Brakes....
I really am concerned about this condition on my car... the rear wheels are toed in really bad and I'm blowing through tires on the inside edge.
Thanks,
Roc
Racer
Joined: Mar 2005
Posts: 294
Likes: 1
From: Racine Wisconsin
The photo is rotated 180 degrees for some reason. I use a dial indicator attached to a piece of iron, held to the steering knuckle with a Vise-Grip. I have the rotor held on with two nuts. I've heard that when shimming, it is good to have all the nuts on tight as the rotor can distort when all nuts are torqued down. I plan to do that next time.
The procedure is to mark the high spot (or low spot) and rotate the rotor on the hub around 180 degrees (i.e 144 or 216), then to see if it improves. Ultimately, indexing it in 72-degree increments to find the lowest runout. After that shim the low side with around 1/2 the thickness of the total runout. If that is correct, then one may wish to support the adjacent bolts with around 2/3rds of that thickness. There is a product sold at GM dealers called BrakeAlign that is a tapered ship that comes in various thicknesses. I have not tried it.
Race Director
Joined: Nov 2002
Posts: 12,142
Likes: 54
From: Taylor Michigan
WTF...Dial indicators and Shims?.
Corvette brakes are the same as any other car. If your attempting to true up rotors that your just replacing pads on with rotors out of round, what that is telling you is to get the rotors machined. The fronts are super easy by chucking them up on the races. The rears are just as easy when finished with a FWD hub-less rotor adapter. Any quality auto parts can do the job. Good machines are a plus though. Any store with a 'Van Norman' drum and rotor lathe will make them dead nuts every time. Screwing around with dial indicators and 'shims' is a waste of time. We have cut hundreds of rotors for customers on every conceivable car. Also my service center did several brake jobs a week without a incident. And yes we do Vettes... 
A previous reply mentioned that even new rotors can be out of round. He`s correct, we have to cut them too. So pulling them from a box, we always check them on the lathe to see if there true as a large percentage may not be. Time to us is money. If you cant do them right the first time, how the hell will you have time to do it a second time....
A previous reply mentioned that even new rotors can be out of round. He`s correct, we have to cut them too. So pulling them from a box, we always check them on the lathe to see if there true as a large percentage may not be. Time to us is money. If you cant do them right the first time, how the hell will you have time to do it a second time....
Melting Slicks
Joined: May 2007
Posts: 3,246
Likes: 4
From: Bay Area CA
FYI, i used a unique solution with my 4 new rotors, took the 'Vette to the Chevey dealer and had them turn the rotors on the car, with one of the new 'bolt to hub' machines. Several hundred miles now,, no fade or air. just make sure when you get the car back, to remove each tire and spray a dot of paint on 1 lug, and rotor hole, to install them back correctly, if you ever remove them again. they will be true in the position they were turned in.
Last edited by RunningMan373; Aug 26, 2008 at 03:28 AM.
Melting Slicks
Joined: Nov 2001
Posts: 2,668
Likes: 43
From: Eastern US XX
Would it not be better to pull the two front hubs and press out the studs, then take the hubs to a machine shop and have the faces turned untill the hub are running true, that would end all future problems when replacing brake rotors........
I would think that brand new rotors are running true and paralell, since almost everting made today is manufactured on a CNC machine.
I would think that brand new rotors are running true and paralell, since almost everting made today is manufactured on a CNC machine.