rotor grinding against brake calliper carrier

[electrofelix]

Recently did an overhaul of my brake callipers which involved cleaning, stripping, rebuilding and painting them.

During this process I noticed some unusual wearing on one of the rear brake carriers. While I was careful about not mixing up the brake pads, I wasn't so careful about the calliper carriers so I wasn't sure which side the wear was occurring on.

Over the recent weekend, while refitting the rear left along with a new brake hose and pipe (stripped the nut on the brake pipe) I noticed that the brake disc would not rotate around smoothly like it did on the right side and instead would grind against carrier. Likely this explains the additional wearing I had seen on the brake carrier, which ended up on the opposite side. When looking at the brake disc, it's the side facing out that comes into contact with the carrier.


A quick fix would be to swap the calliper carriers around, but that is just avoiding the problem: why is the rotor coming into contact with the carrier at all.

Before someone suggests warped rotors: http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml suggests that is not a particularly useful term.

I also doubt that brake pad deposits are responsible here, they shouldn't be able to build up enough to get that close.

Possibly there are some cracks on the underside which has resulted in a cone effect on the brake disc, but it's not clear if this would cause it to come into contact with the carrier or just result in vibration under braking. See Figure 2 on the stoptech site linked above.


I plan to take both the rotor and carrier off and use a wire brush to clean out the hub and back of the rotor and the area the carrier is bolted too to make sure it's not due to debris.


Any other likely possibilities to be looked at?

[NLu]

What are you referring to as the "brake carrier"?

Are you talking about the caliper bracket that bolts to the rear trailing arm? Or are you referring to the actual trailing arm? or the dust shield?

My rear dust shield was bent, and my rotor was rubbing against it. Had to get a new dust shield, as I wasn't able to re-bend it properly.

If your rotor is actually contacting the caliper bracket, then that's altogether a different issue...

[Spyke]

Only time I've really seen that happen was a carrier bolt loose (not tightened down all the way/or stripped so it won't lock fully down) or snapped bolt...

[choffa]

Realoem.com shows both brackets are same. Check rotors for rust buildup on outer diameter grind off if it is contacting the carrier (or replace rotors). If rotors are warped enough to contact, would expect you're feel it when braking. Damaged wheel bearings bad enough to rub would be very obvious (noise).

[electrofelix]

What are you referring to as the "brake carrier"?

If your rotor is actually contacting the caliper bracket, then that's altogether a different issue...

It's the "altogether a different issue" one :(
See part 2 is the carrier I'm referring to: http://www.realoem.com/bmw/showparts.do?model=BE52&mospid=47425&btnr=34_0567&hg=34&fg=10&hl=60



Only time I've really seen that happen was a carrier bolt loose (not tightened down all the way/or stripped so it won't lock fully down) or snapped bolt...

Both are correctly torqued down and while I don't see that there could be sufficient material between the carrier and the mount points on the rear trailing arm to result in the carrier being off line enough to come into contact with the rotor I plan to remove and clean the mount areas with a wire brush just to be certain.


Realoem.com shows both brackets are same.

Indeed both are the same so it's possible to swap them around which is what I accidentally did when putting them back on the car. The additional wearing on the carrier that ended up on the other side and the fact that I hadn't previously had a grinding problem on this side indicates that this had happened previously before I had the car.


Check rotors for rust buildup on outer diameter grind off if it is contacting the carrier (or replace rotors).

Would still mean that there is something wrong, as even with rust it shouldn't result in being close enough.


If rotors are warped enough to contact, would expect you're feel it when braking. Damaged wheel bearings bad enough to rub would be very obvious (noise).

Warped rotors are a bit of a misnomer, http://www.stoptech.com/tech_info/wp...rakedisk.shtml, there is a distinct term for each of the issues that tend to get bundled up and called warped rotors. Only one of the issues mentioned on the stoptech site that I can see it being is cracks on the rear side with a cone effect.

Certainly the wheel bearing was in reasonable condition before, possible coming close to time to replace it, but no audible indications that it was worn out. I'll check it out anyway with the carrier off.


Seems the possibilities are pretty limited

carrier not sitting correctly
cracked underside of the rotor
serious wheel bearing failure completely unnoticed by me


Is it possible that the car was hit at some stage and there is something bend on the RTA? i.e. carrier mount points or the hub?

[choffa]

Check all rotating elements for runout with a dial indicator. Hub face, then rotor mounted on hub. Be sure to clean hub face and mating surface inside rotor. Since the contact is intermittent some component isn't running true.

http://www.raybestos.com/wps/wcm/connect/7c99310046c706cc8c37be66d05ee771/BPI-03-02rev6-06.pdf?MOD=AJPERES

[electrofelix]

Check all rotating elements for runout with a dial indicator. Hub face, then rotor mounted on hub. Be sure to clean hub face and mating surface inside rotor. Since the contact is intermittent some component isn't running true.

http://www.raybestos.com/wps/wcm/connect/7c99310046c706cc8c37be66d05ee771/BPI-03-02rev6-06.pdf?MOD=AJPERES

Excellent advice. Picked up a dial indicator and magnetic stand and checked both hub and rotor.

Hub run out = ~0.9mm :eek:
Rotor run out = ~2.8mm

Since the rotor run out occurs at the same point it could well be all down to the hub being out.

[JDStrickland]

It's time to measure the rotors to be sure they are the same -- especially if you bought the car with these rotors on it, and are just now getting around to servicing the brakes.

Since the carrier mounts to the same thing as the rotor -- they both mount to the outboard end of the axle housing -- then it seems unlikely to me that an accident could make the problem you are having.

If the axle does not seat fully into the housing, then the rotor could rub on the brake carrier.

[electrofelix]

It's time to measure the rotors to be sure they are the same -- especially if you bought the car with these rotors on it, and are just now getting around to servicing the brakes.

Not sure what this would accomplish, as the problem isn't that the brake discs are too large or too small, a quick look that their position relative to the carrier on each side showed that, and looking at the clearance between the disc and the carrier indicated that the thickness isn't the issue either.


Since the carrier mounts to the same thing as the rotor -- they both mount to the outboard end of the axle housing -- then it seems unlikely to me that an accident could make the problem you are having.

I was thinking more along the lines of the hub having been bent, but yes probably unlikely that the carrier could bend the housing without taking noticeable damage.


If the axle does not seat fully into the housing, then the rotor could rub on the brake carrier.

Could you elaborate? I would have though that it was the hub + wheel bearing that would be more likely to cause that?


First stop is the rear hub, since besides the run out, there was visible unevenness, even after cleaning it to make sure there was no dirt, means that a large part of the problem is there.

[JDStrickland]

SWAP THE ROTORS and see if they switch the problem to the other side.

I was suggesting that the distance to the rotor surface from the hub surface is different, causing one rotor to strike the caliper mounting bracket.

The bracket and the hub should be in the same place on both sides of the car -- the distance out from the center of the car should be the same (assuming the diff is in the center, but it is not so you can't really use this as a measurment.). If the car was struck in such a way as to bend something, the axle and brake components would retain the same relative positions, so a bent lower control arm, that sort of thing, would not be part of this problem.

If the axle shaft has been taken out and put back in, but not seated fully, then the hub and brake parts would not be in the proper orientation, and the problem you are having could exist. It seems to me that there would be other problems at least as bad as this one, and perhaps worse, so I discount this as a possible problem. But you should look, I suppose.

If you swap the rotors and the problem moves to the other side, then the rotor itself is the problem. Wrong part for the car, something like that. If the problem remains on the same side, then the orientation of the hub (axle shaft) and axle housing would be the likely suspect.

[freddybeemer100]

What you have is "mushrooming" of the edge of the rotor. It gets deformed after a while and develops a "lip" which comes in contact with the caliper mounting bracket.

Just grind the lip off the edge or replace the rotors.

[electrofelix]

Just a quick follow up. The run-out on the hub was the main culprit which was fixed by replacing it.

As an interesting aside, when replacing the wheel bearing (comes apart when you pull the hub), I noticed that it wasn't properly in the housing. Ever so slightly off centre, just enough to make it difficult to move one side of the circlip, and some dirt to be cleaned out from the same side behind the bearing once removed. Wouldn't have caused the lateral run-out, but certainly exasperated the problem by causing some toe-in relative to the housing and calliper carrier.



SWAP THE ROTORS and see if they switch the problem to the other side.

I was suggesting that the distance to the rotor surface from the hub surface is different, causing one rotor to strike the caliper mounting bracket.


With 0.9mm on lateral run-out in the hub alone, there is guaranteed to be at least 1.6mm of lateral run-out at the each of the rotor. Until I fixed the problem with the hub I figured that swapping the rotor was unlikely to fix the problem, and I could always do it once the hub was fixed.


The bracket and the hub should be in the same place on both sides of the car -- the distance out from the center of the car should be the same (assuming the diff is in the center, but it is not so you can't really use this as a measurment.). If the car was struck in such a way as to bend something, the axle and brake components would retain the same relative positions, so a bent lower control arm, that sort of thing, would not be part of this problem.

Thought perhaps an impact with a kerb on the rear wheel might be responsible. Certainly with damage to the hub, the brake disc not sitting flush with the hub surface and the wheel bearing slightly off centre it seems likely that all three are connected.


If you swap the rotors and the problem moves to the other side, then the rotor itself is the problem. Wrong part for the car, something like that. If the problem remains on the same side, then the orientation of the hub (axle shaft) and axle housing would be the likely suspect.

I'll look at that if there is still any remaining run-out (visually looks to be gone), haven't done a proper measurement since the hub replacement.