Brake rotor "runout" - ZR-1 Net Registry Forums

Aurora40 · 10-05-2008

I believe runout is the term. Anyway, when I spin the front driver's side rotor, it will drag on the inside brake pad on one area of the rotor. There is clearly some variation in where the rotor is in relation to the caliper as the rotor spins.

So what I did was mark the area where it seemed to drag. Then I pulled the caliper off and took the rotor off. I spun the rotor on the hub 144 degrees (two lug nuts) and locked it down again with two lug nuts. I put the caliper back on. This is a fixed caliper, so it shouldn't have moved in relation to where it was previously. I then rotated the rotor and marked where it drags. The drag mark had moved about the same amount as I rotated the rotor.

This means it's not the rotor that has the variation, correct? Or is that not a valid way to check? Also, if it's not the rotor, what would it be, the wheel bearing? Or just the mounting area isn't flush or something? I guess I figured if the bearing were out of whack, it would still rotate properly, but the whole rotor might be at an angle when rotating.

I tried shaking the wheel top to bottom, and it didn't appear to have any movement.

From dealing with shims the last few weeks, I'd guess the runout in terms of how far it moves from the pad would be in the area of 0.01-0.02". Not a lot, but clearly visible. My guess is this wouldn't be hugely problematic, but I'd like to fix it.

karterdon · 10-05-2008

Check the mating surfaces of boththe rotor and the hub make shure that there is not a piece of dirt / excess metal / burr ot somthing that would cause the rotor not to sit completely flush. For grin sake - Take your old rotor if you have one and see what you have. - Run out on the wheel beering and hub should be .000 you may have some slight deviation / run out on the rotor a couple of thousandth .002 is very permissable - The only correct way to measure is to use a dial indicator and not shims or a feeler guage. You might even want to take a piece of emery cloth and clean both mating surfaces of the rotor and the hub.

Good luck.

Don Yoakem
91-#267
Dark Red Met.

10-05-2008

It does sound like you have a piece of garbage sitting on the flange or the base of one of the lugs.

I agree with Don on proper measurement.

10-05-2008	#1
Aurora40 Join Date: May 2005 Location: Leesburg, VA Posts: 2,713	Brake rotor "runout" I believe runout is the term. Anyway, when I spin the front driver's side rotor, it will drag on the inside brake pad on one area of the rotor. There is clearly some variation in where the rotor is in relation to the caliper as the rotor spins. So what I did was mark the area where it seemed to drag. Then I pulled the caliper off and took the rotor off. I spun the rotor on the hub 144 degrees (two lug nuts) and locked it down again with two lug nuts. I put the caliper back on. This is a fixed caliper, so it shouldn't have moved in relation to where it was previously. I then rotated the rotor and marked where it drags. The drag mark had moved about the same amount as I rotated the rotor. This means it's not the rotor that has the variation, correct? Or is that not a valid way to check? Also, if it's not the rotor, what would it be, the wheel bearing? Or just the mounting area isn't flush or something? I guess I figured if the bearing were out of whack, it would still rotate properly, but the whole rotor might be at an angle when rotating. I tried shaking the wheel top to bottom, and it didn't appear to have any movement. From dealing with shims the last few weeks, I'd guess the runout in terms of how far it moves from the pad would be in the area of 0.01-0.02". Not a lot, but clearly visible. My guess is this wouldn't be hugely problematic, but I'd like to fix it. __________________ Bob Saveland Former owner of #2517 [IMG]http://a.random-image.net/aurora40/vette.jpg[/img]

10-05-2008	#3
Jeffvette Guest Posts: n/a	Re: Brake rotor "runout" It does sound like you have a piece of garbage sitting on the flange or the base of one of the lugs. I agree with Don on proper measurement.

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10-05-2008	#2
karterdon Join Date: Jan 2008 Location: Antioch, Illinois Posts: 129	Re: Brake rotor "runout" Check the mating surfaces of boththe rotor and the hub make shure that there is not a piece of dirt / excess metal / burr ot somthing that would cause the rotor not to sit completely flush. For grin sake - Take your old rotor if you have one and see what you have. - Run out on the wheel beering and hub should be .000 you may have some slight deviation / run out on the rotor a couple of thousandth .002 is very permissable - The only correct way to measure is to use a dial indicator and not shims or a feeler guage. You might even want to take a piece of emery cloth and clean both mating surfaces of the rotor and the hub. Good luck. Don Yoakem 91-#267 Dark Red Met.