Problem with M rotors

[mhughett]

I bought my M Coupe 4 months ago with 7.8k miles on it. It was bought from the local BMW dealer and prior to purchase, I asked for and was given a service history on the car. What seemed strange at the time was that not once but twice, the car was serviced for the complaint of "vibrations while braking". The service advisor says that it got new front rotors and pads the last time. However, I've had the car now about 4.5k miles and it's doing it again. It's definitely the front brakes as it only happens while braking from higher speeds and you feel it in the steering wheel. It is quite annoying.

This seems unusual as I have a BMW 530i that has 83k miles on the original rotors with no vibrations whatsoever. I've also read many people say the M rotors do not normally warp. So is there anything else that could be causing the vibrations? Wheel bearings? bushings? I've looked closely at the rotors and I do NOT think there is any irregular pad deposits. The car is going in tomorrow for its scheduled oil service and I'm having them check the run-out of the rotors too. I'm hoping they can find the source of the problem and not just put new rotors on again. We'll see.

[wrh3]

Try bedding in the brakes again, this is the fix when I have this issue:

http://www.zeckhausen.com/bedding_in_brakes.htm

[mhughett]

I tried that early on. No effect. That's why I think it does not have the problem with deposits on the rotors.

[doozyj]

Rotors are toast then, this happened to my M3 E46 and if rebedding doesn't work they need to be replaced.

[Shipkiller]

I had the same issue on mine. I ended up taking the rotors off, cleaning them and them rebedding the brakes. Issue fixed.

Checking the runout on these rotors (drilled) is a MAJOR pain and most shops just will not do it.

[onebluemcm]

And it's not the normal groan/vibration that happens with the drilled rotors? You didn't mention if you've driven a car with drilled rotors before. I hadn't before the Z4M - had an E46 M3 before it. They are definitely different.

I suspect you know this and what you are experiencing is something else, just thought I throw this out there on the off chance it's just the drilled rotors doing what they do.

[ga41]

Originally Posted by Shipkiller

I had the same issue on mine. I ended up taking the rotors off, cleaning them and them rebedding the brakes. Issue fixed.

Checking the runout on these rotors (drilled) is a MAJOR pain and most shops just will not do it.

What do you mean cleaned them? How do you do that? Mine doesnt vibrate when braking hard but it's good to know anyway.

[mhughett]

I'm guessing that "cleaning" means resurfacing the rotors with some sort os sanding device. I saw a thread not too long ago where the rotors were sanded down with a paint stripping wheel attached to a drill. That assumes there is a deposit problem and not warping.

[Shipkiller]

Rotors very seldom, if ever warp, when driven in a street enviroment.

I used a scotchbright pad (or simmilar) and brake cleaner and scrubbed them.

I would never use any type of sanding type wheels on ///M rotors. The lateral runout specifcation if I remember correctly is .005" and you really could screw up a $250.00 rotor that way.

[mhughett]

Well, my service advisor said that I need new rotors as the current ones did not pass the run-out spec. So much for not warping. As expected, not in stock and I had to leave the car for an extra day. I hope that this problem was the result of bad habits of the prior owner and not something with the car. I've got 84k miles on my 530i with the original pads and rotors and no vibrations so I know it's not my driving habits. It will be nice to start out with a new set. Let's hope these turn out better.

[bosstones]

Originally Posted by Shipkiller

Rotors very seldom, if ever warp, when driven in a street enviroment.

Older model Jeep GC's were notorious, from what I understand, for warping the OE rotors due. Then again, the rotors sucked anyways. I've been much happier w/ my cryostop rotors.

[Shipkiller]

Originally Posted by mhughett

Well, my service advisor said that I need new rotors as the current ones did not pass the run-out spec. So much for not warping. As expected, not in stock and I had to leave the car for an extra day. I hope that this problem was the result of bad habits of the prior owner and not something with the car. I've got 84k miles on my 530i with the original pads and rotors and no vibrations so I know it's not my driving habits. It will be nice to start out with a new set. Let's hope these turn out better.

Ask him what the run out spec is. He most likely does not know, and it is extremely difficult to do a lateral run out on drilled rotors. It is damn near impossible with a clamp on dial gauge…. You need a bench setup where you pull the rotor off and put it in a special setup. 99% of all dealerships don’t have these specialized systems. Not cost effective for them.

I drive my car every day and have had eight track days this year and my rotors are not warped….

I am not saying that yours are warped or not warped. It is just most people don’t understand really how a brake system works. Even the so called techs at the dealers.

The most likely scenario is that they just don’t want to bother with any of that and pronounce that the rotors are warped and will replace them

Ether way, you get a new set of rotors at approx. $250.00 each..

[onebluemcm]

To add to WHS ^

The only time I've ever personally had vibration from warped rotors on a street car was on two occasions with very high mileage cars and beyond wore out rotors. Once enough material is removed from the rotor, it cannot handle heat well and will warp under conditions that would not make a normal, full thickness rotor warp. This seems unlikely in your situation with everything being quite new.

So you let them foot the bill for new rotors - if you aren't paying for it, fine. What I would be worried about is why this has happened twice. Is there something else wrong? On new, or low mileage basically CSL brakes, which I believe is what this is, I think it would be extremely hard to warp the rotors - I mean, you'd have to be unbelievably hard on the brakes daily to attempt this. Also seems kind of unlikely in your situation.

If it were me, and having dealt with the two local dealers around here, I would be asking for the most senior or experienced tech to work on the car and check other parts of the brake system and suspension to make sure something else isn't the matter. I cannot think of what else might be wrong to either warp new rotors with out a obvious problem while driving, or that might make a vibration similar to a warped rotor. So, I think it would be very, very important to have it looked over by someone who really pays attention to detail and is meticulous, which can be hard to find at a dealer. Or, as unlikely as it seems, maybe it is just warped rotors......

[z4mcoupe]

I had the exact same problem described by OP. I bought the car in July after the dealer replaced the rotors because of vibration felt only when applying brake.

Three months and 6K miles later, same issue came back. I brought it in for Inspection I and had them look at the front rotors again. They determined the rotors were warped prematurely due to user's abuse and BMW might not cover it. I asked them to define "user's abuse" and the explanation was along the line of how one should drive such a car. No track use during this period by the way.

In the end, the rotors were replaced and covered by BMW. Vibration is completely gone.

[R32]

hm- if your dealer is replacing the rotors, ask to keep the old ones- i'd bet they're nothing wrong with them that a little brakleen and scotchbrite pad can't fix.

that way you'll have spares, or you can sell them to the track rats around here!

[mhughett]

I would love to keep the old ones but my advisor says they have to give the old ones back to BMW for "evaluation" purposes. Maybe they get some sort of a credit from the manufacturer--I don't know. If I ever get in a similar situation where the rotors are no longer covered, I'll definitely take the scotch-brite and brake-kleen to them and see if that doesn't help before I go out and spend $250/rotor.

[Mike Clark]

The brakes on myM roadster have over 30,000 miles with no issues. Sometimes the car will sit for a week at a time and build some rust on the rotor in humid Florida summer, but it comes off quickly when driven and no warping or stopping issues. I've had some American cars (last was a Lincoln LS) where the cheap rotors needed to be turned or replaced every 20,000 miles.

[mhughett]

Originally Posted by Shipkiller

Ask him what the run out spec is. He most likely does not know, and it is extremely difficult to do a lateral run out on drilled rotors. It is damn near impossible with a clamp on dial gauge…. You need a bench setup where you pull the rotor off and put it in a special setup. 99% of all dealerships don’t have these specialized systems. Not cost effective for them.

..

Picked up my car today with the new rotors and no vibrations. The advisor was very thorough about checking everything out in the braking system to see if there was something else wrong that caused the problem. They first took the car out and verified the vibration. Then the ticket reads as follows "Measured 0.002" on left and right front rotors. I contacted my FSE to see if there was any issues with rotors warping prematurely, FSE (Name) did not find any issues concerning rotors. FSE recommended rotors be replaced and vehicle test drive to verify fix. Replaced front rotors and verified fix. No vibration felt when braking at highway speeds".

Per my request, they also checked for any loose motor mount bolts and none were found. All I know is that the brakes now feel so much better.

[Alicate]

Make sure the torque on the lugbolts is at spec and avoid an impact wrench to tighten the bolts. Unevenly torqued or overtorqued wheels can produce vibrations and eventually contribute to rotor warpage. This may have been the 'bad habit" from the PO that caused the problem.

[The HACK]

Originally Posted by Alicate

Make sure the torque on the lugbolts is at spec and avoid an impact wrench to tighten the bolts. Unevenly torqued or overtorqued wheels can produce vibrations and eventually contribute to rotor warpage. This may have been the 'bad habit" from the PO that caused the problem.

Not on a 2 piece floating rotor.