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Old 12-26-2011, 09:34 AM   #10
Registered User
Join Date: Jun 2011
Location: Edmonton, Alberta
Posts: 278
My Ride: 2002 325i,2003 330ci
Originally Posted by MJLavelle View Post
It sounds most like the piston is not floating on the two guide pins. The actual piston itself does not get lubes, except with brake fluid, as it moves in and out. But the two pins the caliper floats on can get gummed up with dirt and old grease, and the caliper does not move in and out properly. It can get cocked to one side, and stick there, and cause the problem you are seeing. Just breaking it loose and moving it in and out a few times may clear the issue, but if you can pull the caliper off, and get some new caliper grease on there, it should work fine. This is the most common problem encountered. There could be other issues, such as a piston that is not moving correctly, but it most likely is just some gummed up pins that the caliper slides on. If her father has some experience with cars, then he should be able to diagnose that, and fix it fairly easily. The guide pins are item #6 in the attached drawing. They are smooth, and protected by rubber boots. It is not the best representation, so you may want to look up a DIY for brake pad replacement, to get a better view. I hope I was able to post this in time to be helpful, but I think I may be a bit late. Good luck.*

Thanks for taking the time to post. I am crossing my fingers that it is just gummed up guide pins. I know how the braking system works, my train of thought is not that the piston is requiring lube. But if the piston is sticking some lube around the bore may help it to stay free long enough that the car can make it home.

I will be going over the brakes pretty throughly once it gets back home, I've already done a nice clean up and overhaul on my 325i. I just haven't had time to do it on the xi since I bought it, and the PO said they had just done front brakes before selling. Just goes to show you can't trust anybodies workmanship but your own.
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