I changed out rotors and pads on my C5 today and it went very easy. Undid the top caliper bolts then the caliper swung down, but had to remove larger bracket to replace rotors.

When everything went back on, it fit to the "T", just like it came off. I can't see how it could do anything other than go back on EXACTLY as it came off.

Now, the problem - Put the wheel back on and torqued down the lug nuts. While still on jackstand and suspended, I gave the wheel a spin and the back of the caliper on the left side is dragging when it comes to the lead balance weights on the inside of the wheel.

Said, this isn't right- took the wheel back off, double checked everything - all was tight and in proper place. Put wheel back on, and moved it around a couple of lugs so it didn't go back on exact, and it is STILL rubbing! The rear part of the caliper is just barely scraping the stick-on led balance weights.

Took for drive and bedded the brakes in... all felt fine. Got back and it doesn't scrape anymore, but about 1/32 to 1/16 of an inch has been scored into the weights, so something it is still not right.. but what?

Anybody got any ideas? I'm at a dead end on this one!

 

probably not the exact same size rotors. some forum members have had to shave the calipers slightly to fix this problem. are the rotors the same size?

 

Actually everything may be in a different place than it was before you took it apart. If the new caliper hub is a different thickness, the wheel will be farther away or closer to the hub and other brake components. The new pads will position the calipers differently due to the new thickness of the pad material in comparison to the thickness of the old worn pads. It sounds like a combination of small variables what is causing your problem. The best solution is to put on new weights (exactly as the old ones) moved over far enough to clear the calipers.
If you put new pads on a stock brake setup, the calipers will be moved towards the outside of the wheel due to the new pads being thicker than the worn ones. You didn't exactly describe which way things moved, but I think this is your problem.

 

alanh
I think I understand what you are saying. When the caliper assembly is bolted back on, it hasn't (nor won't) move forward or backwards. But, due to the new pads, the caliper assembly is moving sideways which puts the outside of the caliper closer to the outside edge of the wheel, yes?

I had not thought of that possibility. I did not check the rotors but they do appear to be the same, only maybe a little thicker, which would further account for this.

I did have to use a C-clamp and push the pistons almost all the way in to get them back on over the new rotors (pad and rotor thickness).

BTW - I don't recall even noting the distance of caliper clearance from the weights before, but now they are scoring the weights almost in the middle of weights (they are about 1/2 inch wide). With time and wear, the calipers will move closer together and thus it would be a good idea to move the weights more towards the outside of the wheel, yes?

I've got the magnesium wheels, and wondering how you get all that glue stick-um off the wheel, when moving/replacing them.

Great catch though! That seems to make the most sense.

 

Sounds like you have figured this one out. Also sounds like you have aftermarket wheels. I have CCWs, but the clearance isn't nearly that tight. Or else you have really thick wheel weights.

I change my race wheels all the time and have to replace the weights frequently. I probably don't care as much as you do about marking my wheels, but I just scrape mine off. You may be able to peel them off with heat (like a blow dryer). You can get double sticky back sponge tape to hold them on again at most stores like Walmart. I also use silver heat tape to tape over them which helps keep them on and hides them somewhat.

Good luck.

 

The Magnesium Wheels were a GM upgrade option in 99. First time I took the wheels off, I could not beleive how light they are. Mostly tire and 'air' weight - the wheels alone must not weigh anything!

 

I would tend to suspect the rotor with the location of the tapped holes drilled in it and the hub and diameter dimensions that ultimately position the caliper bracket (and thus the caliper) and the brake assembly relative to the wheel. Since you replaced both pads at the same time, the caliper should always be positioned the same relative to the rotor as it is self-centering because it floats on the guide pins and the pads generally wear evenly, leaving the caliper centered. If one of your pads was thinner, that would push it in or out depending on it's position in the caliper. When you replace pads, the extra pad thickness is taken up by compressing the pistons, not by moving the caliper sideways. You should be able to trace down the problematic dimension by measuring the critical dimensions on one of the old rotors and the same features on one of the new ones. That should reveal the new interference.

 

diyguy,
You got the idea now. There is very little room between the calipers and wheels, and the repositioning of the calipers due to new pads and rotors can be enough to cause the problems you describe. Usually the rotor thickness doesn't wear that much, as compared to the pads (you didn't say if the new rotors were aftermarket or stock) but when everything is added up after the new install, your problem can happen. If you put on after market rotors, the rotor blade may not be located exactly with the same offset as the stock ones. This could also be part of your problem, even if it's only 1/16 inch, when added to the thickness of the new pads, it will all add up.
I would use some heat (hair dryer) on the weights, then some solvent (mineral spirits OK, not laquer thinner) to get the remaining glue off the wheels. Take good care of those mag wheels. Good Luck

 

Thanks for the tips. They all help me understand the dynamics of what happened while I was doing the mechanics but not understanding the subtle nuiance of change. It must be the rotor difference (and pads). The rotors came from NAPA Pt 86700 and 86701. They were not expensive by any means and 'looked' the same, but I didn't measure them exactly or lay on top of the other for comparison.

Too late for all that now. Just so long as they are safe and can take the heat (pun intended!) Been to rainy out to get them up to speed and stomp on them, although did bed them 6 or 7 times from 45-50 down to 5 MPH.
The pads were ordered from AutoZone - they are PFC Z pads. which should handle the heat and hopefully cut down on the dust a bit. Probably could have gone w/ ceramics, and may still if the dust is really bad...then track days, swap back Z pads.