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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Mechanical Maintenance: Break-in / Oil & Fluids / Servicing / Warranty > Squeaking noise from rear wheel



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      08-09-2012, 07:06 AM   #111
Surly73
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Drives: 2007 E90 328i 6MT sport/prem
Join Date: May 2012
Location: Oakville, Ontario

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I think we might need to create a sticky thread on squeaking.

I've noticed that there are a couple of chronic E90 squeaking issues but with different causes and imprecise descriptions in threads followed by "me too!" are confusing the different issues.

I've also noticed that the shields are awkwardly sized and easily bent compared to other BMWs I've had. It seems almost as if there's one shield for the entire E9x lineup instead of shields properly sized for each model's brake size. My E39 528i (not the largest brakes in the E39 lineup) had shields which exactly matched the rotor diameter. My E90 328i has shields which are significantly larger than the rotor diameter and I've deformed one already when I was removing a wheel. This is one source of squeak/dragging and would probably happen all the time or possibly only under certain kinds of cornering load but it doesn't matter whether the brakes are applied or not.

There's other squeaking which happens when the brakes are applied which people are blaming on the sensor. The sensor shouldn't be coming in contact with anything until the pads are almost worn to their service limit so I'm not sure if I buy this one but I've read it here dozens of times. (OFF TOPIC: I've noticed people credit the brake wear sensors with extraordinary powers of perception which they do not have. The brake sensors do not "measure" your pad thickness, they do not feed into the CBS estimate of your remaining brake life or anything of the sort. When your pads are worn out the metal contact will begin to ground out on the rotor. As the pads continue to wear eventually the contact on the sensor is completely destroyed. If the sensor is grounded or open it turns on the brake pad light - that's it. CBS is a completely separate system to give you an idea of how often inspections need to occur and how long BMW thinks they should last.)

There's also another kind of squeak which seems to be a low-speed "pull away" squeak after being parked. This seems to be parking-brake related. My E90 does it if I've parked downhill using the parking brake. Something keeps dragging and will squeak and interfere with the car rolling freely for the first several feet. If I reverse, tug the p-brake lever it gets things out of the way with no squeak or drag. I haven't disassembled things to see what's going on here but my rear brakes (excluding p-brake) were replaced as part of the safety inspection when I bought my E90 in May.

Finally, brakes naturally squeak unless measures are taken to stop it. This is a high-pitched squeak, not a scrape, and you might here this if anti-squeal paste wasn't used, was improperly applied, or has dried up. You'll hear this when applying the brakes only, and sometimes you'll hear it most at your most common "pedal pressure" but not when braking more hard or gentle than your average. Repeating a "brake job" and re-applying anti-squeal paste should fix this, but not always.
Surly73 is offline   Canada
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