Infamous 335i Brake Squeak

[Bobby G]

by David W. Bynon

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Not long ago, I had an unfortunate parking lot accident with my Porsche. A tired employee backed into my Carrera, crumpling and tearing the plastic bumper cap on the rear of the car. The end result was a $4,200 repair bill. The repair was perfect, but it left me wondering and asking a lot of questions about the use of plastics on cars. Here’s what I discovered.



Most modern cars use plastic bumper systems and fascias made of thermoplastic olefins (TPOs), polycarbonates, polyesters, polypropylene, polyurethanes, polyamides, or blends of these compounds. Often, glass fibers are added to provide more strength and structural rigidity. Plastics allow automotive engineers to have a lot of freedom in styling, building, and placing components.



Plastic also lends itself to combining several complex parts into a single, integrated piece, such as a front bumper and spoiler. From bumpers to door panels, plastics give designers and engineers the freedom to create car shapes and designs that otherwise would never be possible.



With all of its benefits, plastic body parts do have limitations and drawbacks. One of the issues that I have discovered over the years is that painted plastic body parts components easily stain and dull. To understand why, I researched the process of painting plastic bumpers and how it differs from painting metal body panels.



I have long known that it’s necessary to add a “flex� agent to paint for plastics. The flex agent allows the paint to flex with the plastic part and not crack or delaminate. What I did not understand is how the flex agents work. It’s very interesting, and explains why painted plastic parts are so susceptible to staining and dulling.



Paint flex agents cause the paint to be more porous. In essence, the flex agent makes the paint foam, creating microscopic pockets. These pockets allow the paint to remain spongy and flexible. Most of the pockets are deep in the layers of paint, but some float to the surface. The flex agent also causes the paint to remain soft. Paint on TPO resists chips very well, but it will dent (small ping marks) from road stones.



The porosity and softness afforded by the flex agent creates a couple of challenges. First, the paint does not resist stains as well as paint without a flex agent. Second, the flex agent paint cannot be buffed or polished with anything more than the finest polish, or the finish will be ruined. Buffing does not increase the gloss on this paint as it does with a hard paint finish. It smears it.



I’ve seen a dozen or more cases of botched repair jobs, where an inexperienced painter used a buffer to blend paint and put permanent buffer burns and smudges in the bumper cap. I’ve seen even more cases of a car owner using a rubbing compound on their soft plastic bumper caps to remove bug stains. The paint dulls and never returns to full gloss. I have also noticed that etching from hard water and bird droppings is much worse on the painted plastic parts.



General care of plastic bumper caps and fascias is really no different than caring for the rest of the body. Keep it clean and keep it waxed. If you get bug splats, remove them before they harden and have a chance to stain. Low abrasive paint cleansing lotions and polishes are okay to use, but stay away from rubbing compounds and don’t use a high-speed buffer. These areas need waxing more often than the rest of the car, too. Because the front is low and often a complex shape, most people neglect waxing and polishing this area, even though it needs it most.

[Gimlet]

For those of you that do not know, BMW`s 3 series(especially the 335i) is plagued by brake squealing. Pretty much, from what I`ve learned, the design of the wheels and brakes somehow cause the brake dust to build up on the sensor and create the squeaking. When I drive, the car starts squeaking when I accelerate from 0 to about 20 mph. This is extremely annoying because when I am in parking lots, my car just squeaks the whole time causing people to turn heads, but not the way I intended!

I have taken the car to BMW numerous times, and they have tried cleaning the brakes, but to no avail. Changing the brakes seemed to work for about a year, but now the squeaking is back.

Do any of you have any ideas how to get rid of this annoying sound? I heard aftermarket brakes can work, but I still have BMW`s warranty..so thats not an option. Im slowly starting to accept it, but I would really like to see this problem go away. For those of you that are not familiar with it, I have a link of a video (not my car, just one I found on YouTube.)

http://www.youtube.com/watch?v=kxdE12B8QXM

Thanks!

[imported_Stokdgs]

Usually brake squeaking, etc., is caused from vibration, just a tiny bit of runout between the brake pad and the rotor.

Most shops will either put shims behind the brake pad or spray it with a rubber coating, so that it will take up the tiny space and cushion it so the vibration which is causing the sound, goes away.

You could even do the spray yourself if you know how to remove the calipers and take out the pads.

Another place that sometimes causes noise is the pivot points of the caliper itself, which should be lightly lubricated with hi temp brake caliper grease, etc..

Dan F

[Shiny Things]

Jeez, that`s got to be annoying, especially with a nice car like that. This really sounds like a design problem, given what you said you heard from BMW. Under normal circumstances I`d say what stokdgs said, but this sounds like more than something some caliper grease and squeal stop can fix.

[imported_Stokdgs]

Well, I have owned new and used Bimmers for 12 years now, and the only things they ever did was dump a lot of brake dust, because of the pad materials they use.
Maybe it is worth a shot to get the rotors, all 4 of them checked with a micrometer dial indicator, to measure run out anyway, to see if one or more of them is out of spec.
And while its out, it certainly cant hurt to put the shims in or spray the backs of the pads, grease up the caliper mounting points, and see what happens.

Good luck with this !

Dan F

[Gimlet]

Thanks for the replies. Unfortunately I do not believe it cannot be fixed that easily. After a bit more research, I discovered aftermarket pads and rotors can usually stop to the noise. But maybe your ideas can help too. Once the warranty runs out at the end of this year, I will try to find someone who knows what they are doing. If you find anything else about this, please let me know. Thanks again!

[01sugar2]

I`ve been a long term lurker to this message board, but this post happens to pertain to my side of the automotive industry (I`m an automotive technician), and I thought I`d try to chime in with a quick reply. Squeaks and squeals will happen on virtually any brake system out there given the correct conditions, and unfortunately the best way to repair most of them is to simply hide the actual noise.

You`ve already heard from others about a shim or spray-on pad liner that will help with the vibration concern that causes that audible noise that you`re hearing. Another suggestion was to lube up the slide pins on your brake caliper (typically the most neglected serviceable item on all vehicles), and these are all valid statements. The truth is, any time you have metal to metal contact with your brakes, you`ll be prone to having this noise. If you take two pieces of sand paper and rub them together long enough, you`re eventually going to have two smooth surfaces; the same principal applies to brake pads and rotors.

In stating the above, if I had your vehicle, I`d be looking at the face of the brake rotors themselves. A glazed surface (often called a mirror finish) between the brake pad and the rotor will cause your noise concern "almost" every time. It sounds like BMW probably replaced the pads and rotors at one point judging by your initial post. If your rotors have never been turned, I`d recommend starting with that procedure first. Because glazed surfaces will cause those pesky squeaks and squeals, if you`re not going to replace the pads, it`s a good idea to scuff the pad material up a little bit with some sand paper. Sometimes you can even get away with lightly sanding the brake rotors (front and back) instead of turning them on a brake lathe to correct this concern.

A lot of manufacturers out there will claim that their ceramic pads paired with their specific rotors won`t squeak, but in reality, it`s all just a matter of time before the concern once again arrises. If your caliper clip kits are all properly in place and the squealer portion of your brake pads aren`t into the rotors themselves, then I`d be seriously suspecting the surfaces of your brake rotors. Again, have them refinished if they haven`t already been done, and you should hopefully be good to go.

My apology for the long post! Please feel free to respond if you have any questions. I`m sure that many others on this board are more than capable of answering brake system questions as well, so fire away and we`ll go from there. Best of luck, my friend!

Dustin

[Gimlet]

Thanks for the reply Dustin, it was really helpful. I am aware that squeaking happens, as it does on my dad`s car too. But after I give my dad`s car a wash and hose off the wheels, the squeaking stops until more brake dust builds up. But on the bimmer, even right after washing it squeaks.

Unfortunately, I am not skilled enough to start messing around with my brakes and take off the wheels to perform what you mentioned. What kind of shop would I look at taking my car, or would any automotive shop that deals with European cars be able to take a closer look than BMW has been willing to? I am sure there is a way to limit the squeaking, But my local BMW dealer probably doesn`t have the time to really look into my problem.

I really appreciate the reply, it gives me a direction to go in to stop the annoying noise. I`m starting college in the fall, and I am sure the ladies will not be fond of the squeaking haha. Thanks again!

[imported_dpkilty]

Although it may not be specific to your problem, the best advice I can give you is to talk to some local car guys you know. Get their opinions on a local shop. Give that shop a call and talk to them. Then if you feel comfortable with them, have them look at it. Finding a good local shop you can trust is a really great thing. Most businesses "take care" of repeat customers a lot better than John Doe who brings his car in once a year. :2 cents:

Good luck with getting this fixed.