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      02-11-2012, 10:41 AM   #1
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Question Help me diagnose a possible brake issue?

The past few days my Z4M has experienced rough vibration in the steering during highway driving. At first I thought it was an unbalanced or bent rim, but the vibration is not consistent because it doesn't always happen on the same stretch of road day after day.

During cold temperatures of 38 degrees or less the car brakes have squealed very loudly when coming to a stop, however the noise goes away when the temps go above 40.

Last night I took a closer look at the front passenger wheel and found the area to be radiating heat and was significantly hotter than the driver's side. There was also a faint burning smell unlike what a burnt clutch would smell like. From my observation with the wheel still on the car, the rotor doesn't seem to be warped or worn down compared to the driver's side. The outer brake pad also seemed to have the same depth as the other side as well. When I slow down from speed and gradually coast to a stop, there seems to be some resistance where the wheels turn freely but grabs for a split second.

For what it's worth, the dealership didn't notate unusual brake wear in my "Inspection I" service several months ago. I'm also using a 17" winter rim/tire setup and had no problems with it last season. There's no evidence of tire rubbing or wheel weight scraping whatsoever.

I think the passenger side brake pad must be making constant contact with the rotor? How would something like that happen? I suppose I'd need to revert back to the stock rims in case the dealership blames the problem on the aftermarket wheels?
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      02-11-2012, 10:57 AM   #2
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Sounds like a classic case of sticking brake caliper. You didn't indicate if this is a front or rear brake issue.
If its the rear it could be the parking brake shoes not disengaging after a cold night.
Otherwise if its the main brakes you've got a sticky seal preventing the piston from retracting. Dealers will simply replace the offending part, but if your mechanically inclined you'll likely be able to pickup a caliper rebuild kit for a few bucks. Couple hours later you've a rebuild caliper.
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      02-11-2012, 11:07 AM   #3
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It's the front passenger brake. The car is under CPO warranty/extended maintenance plan, so I'll just have the dealership fix it. Thanks for the insight.
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      02-11-2012, 11:09 AM   #4
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If it is not a sticky piston in the caliper, I would say it is more an issue with the floating of the brake caliper. They sit on slide pins so then can center as they apply force, these can get dirty and sticky and cause improper engagment/dis-engagment of the brakes. They are also super easy to check and lubricate.
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      03-04-2012, 09:05 AM   #5
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Quote:
Originally Posted by davesz4mc View Post
If it is not a sticky piston in the caliper, I would say it is more an issue with the floating of the brake caliper. They sit on slide pins so then can center as they apply force, these can get dirty and sticky and cause improper engagment/dis-engagment of the brakes. They are also super easy to check and lubricate.
IIRC they are supposed to be cleaned but not lubricated
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      03-05-2012, 09:33 AM   #6
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So, did the dealer fix the problem?
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      03-06-2012, 07:35 PM   #7
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Turns out the front rotors were worn down. Dealer replaced the front rotors and pads under the extended maintenance program I purchased with the Z4M. I need to invest in a digital caliper for better rotor measurements.
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