What is going on with my M brakes????

[BTM]

Originally Posted by Finnegan

Very light use can cause uneven deposits as well (as can what BTM posted).

Interesting...never thought under-use could do the same...but I like to get a good squeal out of mine by the time I'm parking it

[Finnegan]

Yikes, I probably stated that wrong. More like very light use can make them squeal like you're describing. I need to fix that post!

Fixed. What do you think about the aggressive pad thing? I'll have to see if I can dig up that thread from P9.

[Ron Stygar]

Originally Posted by mhughett

As I stated above, I've tried "bedding in" the pads per the Zeckhausen website to remove irregular pad deposits. I've also done a day at the track. Neither has helped with the problem.

http://www.bimmerfest.com/forums/sho...d.php?t=543625
.
.

[BTM]

Originally Posted by Finnegan

Yikes, I probably stated that wrong. More like very light use can make them squeal like you're describing. I need to fix that post!

Ok makes more sense...

But interesting about your mention of the driving distances after your 1st cycle of bedding...A friend bedded mine as I had never done it before, and he was very cautious after the first cycle, slowing down with gears, parking brake even, and we took a little stint on the highway afterwards...he probably told me but must've slipped my memory that we were in the cooling phase of the bedding process...

The second cycle I did haphazardishly (new word lol) on my own...and FWIW the hotter my pads get the louder they squeal, but they are not OEM and I don't have much experience with the OEM pads as I changed them out after a couple months of ownership...on snow tires

[Finnegan]

Originally Posted by BTM

But interesting about your mention of the driving distances after your 1st cycle of bedding...A friend bedded mine as I had never done it before, and he was very cautious after the first cycle, slowing down with gears, parking brake even, and we took a little stint on the highway afterwards...he probably told me but must've slipped my memory that we were in the cooling phase of the bedding process...

That's the proper bedding approach...at least as I understand it.

Looks like Ron Stygar added another candidate to the list of possible causes.

Take a look at this thread and this thread and finally this thread. Other possible causes are discussed as well as "cures", but the consensus over there is that warped rotors are pretty much an extinct species these days and pad deposits are the most likely cause. That's not to say they aren't warped but that deposits are the most likely culprit.

We're not seeing a lot of warped rotors on the forum, so I don't suspect a production issue or other rotor sourcing problem. In the OP, there was mention of "very light braking". Very light but long braking will heat up the rotors more than heavy/short braking. Is it possible you're heating up the brakes a lot via prolonged light braking and then staying on the brakes (e.g., long braking periods followed by an extended stoplight or stop). That might leave deposits?

[inTgr8r]

One other thing to keep in mind re the bedding process.

If you have deposits its best to scour them off first.
One method is to pop in a set of aggressive track pads to take them down.

[mhughett]

I've thought about buying a set of aggressive track pads (i.e. Hawk HT 10) to scour off the rotors to see if that would help. Notwithstanding the fact they would cost about $200 just for the front, since this car is still under warranty, why should I spend this kind of money chasing an unknown. At this point, it's still BMW's problem to fix this and I didn't want to do anything that might give them any reason to deny the warranty claim. As for discussions about deposits and improper bedding, I've been doing brakes on BMW's for 25 years. I know how to properly bed in brakes and I know what NOT to do to avoid deposits. As I said earlier, I took the rotors and pads off looking for a cause. Before putting them back together, I used scotch-brite pads and brake cleaner to try and get off any kind of deposits. These rotors looked like brand new when I put them back on. Unfortunately, it had no effect on the car--hence it is now at the dealer, again. Thanks for all of your input. I'll let you know when I hear something.

[Finnegan]

Hmmm. Sounds like you covered all the bases and have a considerable amount of experience (sorry if any of this came off as questioning your experience/knowledge).

We haven't aproached a "good" answer on possible root causes to addreess your long-term "out of warranty" concerns though. Grrr. Guess we will have wait and see what the dealer says. Since the regional tech guy is involved there's a better chance of getting to the root cause--got my fingers crossed on that.

[antennahead]

Sounds like everyone is approaching this from a pad and rotor standpoint, any chance this might be an anti-lock malfunction?

[mhughett]

Originally Posted by antennahead

Sounds like everyone is approaching this from a pad and rotor standpoint, any chance this might be an anti-lock malfunction?

I don't think so because (1) it doesn't feel like the kind of vibration you get when ABS kicks in and (2) the problem always goes away temporarily when they put new rotors on. Only after 2-3k miles does it seem to come back. I still haven't heard anything from my SA. I'll call him this afternoon and get a status update.

[santov]

I had pad gunk causing an annoying squeeling in the rears of my Jeep SRT8. They were Brembo pads and calipers and a very common problem. The dealers would often swap pads and the obnoxious squeal would return. I didn't want to spend the money on aftermarket pads so I decided I'd dissassemble to see if I could find the root cause. After a very good cleaning my squeal went away for about 15k miles then started to creep back. I was cool with adding "brake cleaning" to the maintenance list.

A good way of getting rid of pad deposits without going through the Z method would be to take the rotors and pads off. Place a piece of sand paper on the ground and lightly rub the pad face down. Maybe 5-10 full circles and you'll see pad material on the sand paper. The surface of the pad should be smooth (you're not usings lots of pressure, just some abrasive to return the pad to factory flat and smooth). Spray with brake cleaner and wipe dry. The pad should be smooth and factory looking clean.

Then use some brake cleaner and metal scour pad to clean the rotors very thoroughly. If they're lightly grooved that's fine. A scour pad won't get the grooves out, but you're trying to get to bare metal and get any deposits out of the surface. Spray with brake cleaner and wipe clean with a rag or shop towel.

Lube and reassemble then re-bed. If it works you know it was the pad build up or the stealers not bedding correctly. I've never had to bed aggressively, I just drive VERY gingerly for 300-400 miles and from VERY gentle use (driving grandma slow for a few days) the pads and rotors are happy. It's like bedding process but without all the crazy heat.

I was thinking it could also be a bent caliper, caliper bolt too tight, or rotor not seated. But those symtoms would show with one corner, not all four.

[mhughett]

I finally got the diagnosis from the SA today. The BMW tech rep suggested that they check the runout of the hubs and they found the left front was out by .002". Right front was fine. Therefore, they are putting on a new hub, bearing and both front rotors and it should be done tomorrow night. I fully expect everything to be fine when I pick the car up but the real test will be several months down the road.

This solution makes sense but it is still interesting to me that it has always been fine initially after getting new rotors but only after a few months of time and after the wheels have been taken off and put back on a couple of times does it begin to exhibit problems. I thought initially that maybe a tire tech was torquing the lugs too tight but I've checked the torque every time to make sure it was perfect and i still had the problem. I think what may have been happening is that if the hub is not turning properly, the more times you put a wheel on and off, it may be forcing the irregularity onto the brake rotors. Not saying this is a fact but just trying to make sense of what's been going on. Thanks to everyone for your input and I hope my experience proves helpful to someone else in the future.

[Ron Stygar]

Originally Posted by mhughett

The caliper pins were lubed and there was no evidence of sticking.

http://www.bimmerfest.com/forums/sho...&postcount=100

[CFoote]

Could it be that someone is over-tightening the lug bolts (i.e dealer)? I know over-torque can cause the rotors to warp on any car...

Chris

[mhughett]

No, I've been checking the torque on the lug bolts every time tires are removed and reinstalled.

[santov]

So did replacing the hub fix the shimmy? .002 is VERY small (there's that much play in the bearing). Did the SA mean .02?

[mhughett]

Originally Posted by santov

So did replacing the hub fix the shimmy? .002 is VERY small (there's that much play in the bearing). Did the SA mean .02?

Actually, from the technical information I've read, it is understood that you can begin to feel the shimmy when the runout gets to .001". My runout on the wheel with the bad hub was .0025. When they replaced it and remeasured, it was .0005, which is within specs. I feel nothing now and it's great.

[Ron Stygar]

Originally Posted by mhughett

Actually, from the technical information I've read, it is understood that you can begin to feel the shimmy when the runout gets to .001". My runout on the wheel with the bad hub was .0025. When they replaced it and remeasured, it was .0005, which is within specs. I feel nothing now and it's great.

Technical Data


mm to inches:
http://www.convertunits.com/from/mm/to/inches


Wheel bearing:


Front brake:


Wheel:


http://www.bimmerfest.com/forums/sho...&postcount=101

[mfanatic325]

What I'm amazed at is how willingly your stealershit provides you with rotor swaps. I've had to abuse the crap out of my rotors in the past 6-7 track days and I could only manage to get my stealershit to replace my rears
My fronts are only off by like 2 millimeters at most

[mhughett]

The difference is that my rotors were like new from a wear standpoint. they could tell that there was no hard use involved. However, they (at least one of them) were apparently being ruined by the bad hub on the driver's side.

[mfanatic325]

Oh, I have no doubt in my mind that the service adviser I ended up working with was all for helping me getting new rotors. The problem was, I somehow still wasn't able to wear down the fronts enough
I just felt cheated lol..after trying so hard to wear everything down to within spec. And I was so sure too that everything was toast. But nOoOoOOoOo

[gnx]

Originally Posted by mhughett

I finally got the diagnosis from the SA today. The BMW tech rep suggested that they check the runout of the hubs and they found the left front was out by .002". Right front was fine. Therefore, they are putting on a new hub, bearing and both front rotors and it should be done tomorrow night. I fully expect everything to be fine when I pick the car up but the real test will be several months down the road.

This solution makes sense but it is still interesting to me that it has always been fine initially after getting new rotors but only after a few months of time and after the wheels have been taken off and put back on a couple of times does it begin to exhibit problems. I thought initially that maybe a tire tech was torquing the lugs too tight but I've checked the torque every time to make sure it was perfect and i still had the problem. I think what may have been happening is that if the hub is not turning properly, the more times you put a wheel on and off, it may be forcing the irregularity onto the brake rotors. Not saying this is a fact but just trying to make sense of what's been going on. Thanks to everyone for your input and I hope my experience proves helpful to someone else in the future.

I understand that the no1 illustration is basically the bearing, I had my right one replaced a week ago.

http://www.realoem.com/bmw/showparts...&fg=10&lang=en

What exactly is the hub and how does one determine if it needs to be replaced?