fixing rotor runout
Thread Starter
Racer
Joined: Apr 2000
Posts: 430
Likes: 15
From: eureka, ca
fixing rotor runout
since installing new trailing arms ,I have been having the dreaded "low peddle " because of rotor runout. I took my 66 to the alignment shop and they said they could turn the rotors on the car to fix the runout problem. They called later and said they couldn't do the rears , only the fronts. Called another shop and they said the same thing. They said the only way to fix the runout was to get tapered shims from Chevrolet. Is this the only way? Does anyone know where I can get my rotors turned on the car? Would these shims be as good as turning the rotors?
Safety Car
Joined: Nov 2004
Posts: 4,182
Likes: 94
From: going faster miles an hour...with the radio on in browns mills new jersey
I'm pretty sure NAPA has tapered shims.
Because I'm cheap, I fixed a slight runout problem on two of my rotors with an aluminum beer can, a pair of scissors, and a hole punch.
Because I'm cheap, I fixed a slight runout problem on two of my rotors with an aluminum beer can, a pair of scissors, and a hole punch.
Drifting
Joined: Dec 2002
Posts: 1,946
Likes: 28
From: Long Beach CA
I doubt, because of the suspension design, that you'll find anyone who can turn them on the car. I'm assuming the rivets have been drilled and the rotors can be removed easily. Make sure the rotor and hub mounting surface is clean and you don't have crud between the two causing excessive runout. Use a dial indicator to find out how much runout the rotor has. Then try removing the rotor and remounting it on the hub one stud clockwise from where it was and remeasure. Repeat. You may find one position where the runout is below spec. If not, find the position where it is the least, and shim it there.
Safety Car
Joined: Mar 2009
Posts: 4,191
Likes: 951
From: Corpus Christi, TX
You can also have a machine shop grind the rotors while they're attached to the spindles. The runout will be zero. The whole dreaded runout thing is because the factory made the rotor/spindle assemblies that way.
Thread Starter
Racer
Joined: Apr 2000
Posts: 430
Likes: 15
From: eureka, ca
Instructor
Joined: Nov 2004
Posts: 110
Likes: 2
From: Portland Oregon
I found an assortment pack of round arbor shims at Grainger. They come in various thicknesses starting at 0.001" and up. I think the pack cost around $14.00 with shipping.
Came with large enough assortment to do all 4 rotors.
I also tapped the rivet holes and counter sunk tappered head bolts to hold the rotors in place. Dialed runout to aprox 0.002" each.
Came with large enough assortment to do all 4 rotors.
I also tapped the rivet holes and counter sunk tappered head bolts to hold the rotors in place. Dialed runout to aprox 0.002" each.
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Le Mans Master
Joined: Aug 2005
Posts: 6,546
Likes: 1,978
From: Temple Terrace Florida
Runout
I agree with all of the above. If you are in the upper ranges of acceptable runout and you still have air in your brake system, it may be time for O-ring pistons. They are more forgiving than the factory pistons. Jerry
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
I don't think rotor runout will give you just a low pedal. Maybe a "soft, spongy" pedal that picks up pressure close to the floor. There is likely a difference in the cause of the two problems.
Burning Brakes
Joined: Jan 2007
Posts: 1,104
Likes: 12
From: Woonsocket Rhode Island
I did like nassau66427 and used an aluminum can but think that "things go better with Coke" and besides that, the beer cans had a deposit on them.
I also did like LB66383 and rotated the rotors for the least amount of runout before shimming.
If you are not replacing the rivets with bolts, remember to put the lug nuts on and don't attempt to measure runout without the rotor bolted firm. Also check your hub/bearing end play to make sure that is not adding to the problem.
I also did like LB66383 and rotated the rotors for the least amount of runout before shimming.
If you are not replacing the rivets with bolts, remember to put the lug nuts on and don't attempt to measure runout without the rotor bolted firm. Also check your hub/bearing end play to make sure that is not adding to the problem.
Thread Starter
Racer
Joined: Apr 2000
Posts: 430
Likes: 15
From: eureka, ca
I'm pretty sure it's a runout problem. I can drive the car for 500 miles and the peddle gets softer and lower .There is no loss of brake fluid in the master cylinder and just a small amount of air comes out of the lines after bleeding, then the brakes are good for another 500 miles or so.
Thread Starter
Racer
Joined: Apr 2000
Posts: 430
Likes: 15
From: eureka, ca
I found an assortment pack of round arbor shims at Grainger. They come in various thicknesses starting at 0.001" and up. I think the pack cost around $14.00 with shipping.
Came with large enough assortment to do all 4 rotors.
I also tapped the rivet holes and counter sunk tappered head bolts to hold the rotors in place. Dialed runout to aprox 0.002" each.
Came with large enough assortment to do all 4 rotors.
I also tapped the rivet holes and counter sunk tappered head bolts to hold the rotors in place. Dialed runout to aprox 0.002" each.
Team Owner
Joined: Oct 2000
Posts: 38,897
Likes: 1,926
From: Washington Michigan
Team Owner
Joined: Mar 2003
Posts: 26,118
Likes: 1,874
From: Greenville, Indiana
I'm pretty sure it's a runout problem. I can drive the car for 500 miles and the peddle gets softer and lower .There is no loss of brake fluid in the master cylinder and just a small amount of air comes out of the lines after bleeding, then the brakes are good for another 500 miles or so.
Race Director
Joined: Jul 2001
Posts: 15,892
Likes: 42
Another case of fixing something that's just not broken.
Thread Starter
Racer
Joined: Apr 2000
Posts: 430
Likes: 15
From: eureka, ca
The ironic part of the rotor run-out issue is that it is a self induced problem in 99% of cases. For all sorts of reasons people 'feel the need' to swap rotors when there's actually nothing wrong with their existing ones.
Another case of fixing something that's just not broken.
Another case of fixing something that's just not broken.
Pro
Joined: Jul 2008
Posts: 622
Likes: 24
From: Clermont Florida
Your problem is not a warped or wobbling rotor. Niether will cause air to enter the system. A loose wheel bearing, will cause a low pedal, with no pulsation in the pedal. A warped or wobbling rotor can cause a low pedal, with a pulsation. However, with either of these problems, if you apply the brakes, when standing still, the pedal will be low on the first application, but a second application will result in a firm, good, pedal. This is because the loose or warped rotor pushes the pads away from the disk, nothing else. The first pedal push puts the pads back against the rotor, then by the second push, the pads are in proper place, so the pedal feels fine. Low pedal or high, the pedal will be firm, once the travel is taken up and the pads contact the rotor. There will be no soft pedal. Soft means air is in the system. Since you are not loosing fluid, and getting a small amount of air when bleeding, air is entering through a bad caliper. I have seen this problem before. I have also seen this on my vette.
Next time you bleed, any calliper that releases air is a bad calliper, and should be changed. Rich
Next time you bleed, any calliper that releases air is a bad calliper, and should be changed. Rich
Last edited by landshark 454; Apr 25, 2009 at 11:03 AM.