Have a 2009 BMW 328i with 78,000 miles. In the last year, the front brake pads and rotors have been replaced by the dealer 3 times, each time because of “warping” which is their diagnosis of a steering wheel shimmy (left to right oscillation) that occurs under light to moderate braking, especially at highway speeds.
The strange part: replacing the rotors and pads seems to solve the issue, but only for a few hundred miles.
I am led to conclude that something is causing very accelerated uneven deposition of pad material to the rotors - but what could it be? Suspension components and bushings have been inspected and check out. So do calipers. Recently completed: four wheel alignment, wheel rounding and balancing did not solve the issue. One dealer will no longer look at problem until “all four tires replaced” - but tires look fine, they are OEM RFTs with about 4/32nd’s of tread left. Car seems fine cruising on highway - steering wheel shimmy only occurs under braking.
Unfortunately, the car has the sport package and therefore staggered wheel and tires: 225/45 R17’s in the front and 255/40 R17’s in the rear. The good news is that I’ll be mounting the winter wheels/tires in a few weeks - and those are 225/45 R17’s all around.
I have noticed that, whenever I drive my wife’s car, the brakes shudder as I stop, but only for a while. If I drive it in traffic for 20 minutes or so, and use the brakes both to slow and to stop, the shuddering stops and the car works smoothly. So, it’s not that the rotors are permanently warped, because they get better. Like you, I think there is some process going on that deposits material on the rotors unevenly, and it clears off with heat and use. I have no idea what it is, or what makes it happen, or how to avoid it.
This sounds like warped rotors to me. Question is why? You say you have a “sport” package and that might involve some special brake parts. Rotors warp due to overheating. As they cool they warp and loose their shape. Poorly made rotors using inferior materials and/or improper heat treating in the manufacturing process can warp while others hold their proper shape.
Since the dealer is replacing these rotors, they should be of good quality but even parts from good reliable sources can be defective. Have the calipers been replaced? You state disks and rotors which to me are the same thing. You also said new pads and rotors resolve the issue for a few hundred miles - but you don’t say new calipers.
There may be an issue which is not fully releasing the pressure of the pads on the rotors. This will overheat the rotors. Bad calipers could be the reason and I just had to have new calipers put on my truck because they were dragging and not releasing fully.
Your car also has very sophisticated braking control systems, and traction control. These systems work the brakes and perhaps something is wrong and it is applying too much braking.
A dealer should be the best place to sort this out. Since 3 sets of rotors hasn’t resolved the issue I don’t think it is defective rotors, that’s just too many rotors for all to be defective. It could be a design issue and the rotors that they are using are simply too thin. But I suspect it is something in the calipers or the systems that control the brakes putting too much pressure into one or more caliper(s).
This isn’t a build up of brake pad material on the rotors. I just hope the car is under warranty and all these rotor and brake jobs are covered. If you have to take the car back in yet again - ask for a different mechanic to work on the car. At least if it is a error by the installer of the parts a different mechanic should do it right. Some brake pads are right and left pads, some are front and back and a BMW dealer should know how to install the pads properly. But sometimes these brake jobs are considered routine and are given to new and less experienced techs. At this point your brake job is far from routine.
I’d Be Tempted To Install A Set Of Non-OEM Pads. I Don’t Know BMWs, But I’m Wondering If Some Premium Ceramic Pads From A Leading Brake Parts Manufacturer Would Solve The Problem, Especially Since You Seem To Be Suspecting Pad Material Deposition.
Three times with the same parts didn’t work. Why not try something else?
It’s possible for a loose wheel bearing or worn suspension component to cause a problem like this.
That of course raises the question of why it’s fine for a month and if the above were true then why isn’t the worn wheel bearing/suspension component causing it from the start
Often new rotors will warp a few thousandths of an inch once in use. Normally this may not be noticed if everything else is tight but any loose part in the suspension, etc can magnify that few thousandths and make it appear to be worse than it is.
I would hope they are checking the rotors with a mike and dial indicator to verify they’re actually warped at least somewhat badly instead of assuming the rotors are always the root cause of a brake shudder.
I would also hope that new rotors were thoroughly cleaned before installation. Many rotors have a rust preventative substance on them that needs to be cleaned off. Most of the time this substance is not noticeable to the eye. In a few rare cases the substance appears to look and feel like Cosmolene.
I like the idea that the cause is the hubs being bent from a pothole. That would give a tiny rubbing at the very same spot that would result in apparently warped rotors. Using a dial indicator on brand new rotors screwed down tight to the hubs to find the runout when new to see if the bearings/hubs are damaged.
You may also have a slightly dragging pad (due to a sticky caliper) that’s causing the rotor to repeatedly overheat and warp. The best way to diagnose this is to look at the pads. If the caliper is sticking, one pad in the sticky caliper will have more wear than the other.
My daughter had the same problem with a Nissan Altima some years ago. Dealer replaced 3 sets of factory pads and rotors in 15000 miles. (she did drive much faster than most people). At my suggestion she asked him to try a good brand of American made rotors. The dealer was reluctant, saying Nissan wouldn’t pay for aftermarket rotors. She told him, I won’t tell Nissan what you used if you don’t.
zProblem solver, pads and rotors lasted 60000 miles in the rust belt.
I read the article posted by the OP on brake myths. It is a good read. So, my question for the OP is does he see the answer to his problem in that article?
The author states that when a rotor is very hot and the driver comes to a complete stop and maintains pressure on the brake petal then the pads stay in contact with the very hot rotor and pad material will deposit onto the surface of the rotor. This makes the rotor thicker in that spot and eventually leads to shutter felt in the steering wheel under moderate to heavy braking.
The answer is to properly break in the new pads and new rotors and the author gives directions on how to do it properly. A key part of the directions is to do a series of stops of increasing pressure with a cooling period between stops - without coming to a complete stop during this process. At 5 mph the driver is to release pressure on the brake petal and in effect coast and allow the brake rotors to cool.
Once the pads are properly broken in and bedded then complete stops with hot brakes don’t leave the deposits and are no longer a problem.
I like @Mustangman 's idea for a run-out test on the hubs. The run-out should also be checked after the new rotors are installed, on the rotor itself.
If not that …hmmm … .
Is this sports-package you have an BMW approved package? If not, that could be the problem, like the wheel design isn’t properly venting the brakes, so they overheat. Or it is allowing dirt and debris into the brakes.
I think the BMW recommendation to see if new tires helps is a good one.
The brakes might be on all the time for some reason. Do they get hot to the touch after you drive it for 10 miles or so, with little to no braking along the way?
It is possible a driving habit or situation could cause this. Like having a long downhill with a lot of braking on the way to work. Anything like that, something which could be overheating the brakes on a continual basis?
Edit: I frequently see cars on the road ahead of me with the brakes lights on almost the whole way, even though they are going faster than me. And I’m not using my brakes. I don’t think the drivers are aware they are stepping on the brake pedal.
Improperly tightening the wheel lug bolts can turn a good rotor into a warped rotor straight away. There’s a sequence they have to be tightened in, and to a certain torque, no higher. Good shops will tighten the wheel lugs in the proper sequence, but not just one time, 2 or 3 times. To 1/3 the final torque value the first sequence, 2/3 the next, and to the final torque the next. That way the wheel gets snugged up to the hub better. This should be done by hand, not by impact wrench.
With respect to the proper pad-bedding procedure described by StopTech. I tried that the first time new pads and rotors were installed. The problem recurred. The next time BMW installed new brakes and pads they were careful to note that BMW’s breaking-in procedure is the opposite of StopTech’s - they advise to only moderately brake for the first 150 miles. I think this is because high performance aftermarket pads have a different bedding in procedure than OEM pads. I followed BMW’s instruction the 2nd and 3rd times and we got the same results about a month later - the recurrence of the brake judder.
I have been extremely judicious about not overusing the brakes (as a rule, and a driver, I don’t ride the brakes or tailgate and I anticipate stoplight changes). I’ve even gone as far as putting the transmission in neutral so i don’t need to hold the brakes at stoplights against the torque converter creep.
At this point I will ask the shop manager on Monday to ensure his techs are properly tightening the lug nuts by hand, to the required torque specifications, and to inspect run out on the hubs and the new discs when they are inevitably installed.
Of Course It’s Also Important To Be Sure That The Hubs Are Clean, Rust-free, And Debris-Free, Where The New Rotors Seat On The Hubs. If Not, Lateral Run-Out Problems Could Occur. I Would Not Suspect That A BMW Technician Would Neglect This Important Step In Brake Replacement, But…
+1 @“common sense answer”. Any rust will cause rotor runout. Also, caliper pins should be inspected and greased. A sticking caliper will cause the pads to stick against the rotor and overheat the rotors.
The answer is quite simple. Take the car out on a little used road, or any road on a Sunday morning when there is very little traffic. From 60 or so, make a hard stop, not to lock up but just short of that. When you get dow to about 5 mph, release the brakes and accelerate back up to 60 and repeat.
Two or three of these hard 60-5’s should burn off any excess residues. Drive reasonably for a few minutes to let the brakes cool down. You may have to repeat this one more time in a month or two, but after that, you should be good until you need new brakes again.