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Old 06-27-2011, 04:57 AM   #5
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Join Date: Aug 2006
Location: NJ
Posts: 23,679
My Ride: '99 328i 300K miles

If the fronts are getting hot when you're not using brakes...and you have new pads and rotors...then...

* Did you clean all the mating surfaces of rust/dirt before reassembling? The pads only sit 5/1000" off rotor, so a little being 'off' in mating would make a difference. I use a sanding disk on my drill on inside wheel, hub, and if reusing rotors, both sides of it...and clean off well after sanding so you don't have sand anywhere on surfaces or in threads.

* Did you clean the guidepin and guidepin bushing? I personally used brake grease in there after cleaning, though BMW says not too. It has to be brake grease though. (You should also clean where the pads slide on the caliper and dab a bit of grease there too...under where the pad rests on the caliper)

* If the seal on the caliper is broken, then it might be a caliper issue, but if you have access to compressed air, you can blow out the piston and rebuild it with a cheap kit, but most, at that point, just get remanned calipers. (I don't know that you're at that point quite yet, but you may get there)

Finally, I have to say that it did sound a bit like a bearing, because you mentioned the 'whump' noise. I always thought of it as a 'whoop' but perhaps you hear better than me! This doesn't explain the hot rotors, though. See if that noise seems worse in long, sweeping turns, like highway entrance/exit ramps. When load is on wheel, if it's a bearing, it will whoop louder. I doubt it's this because of the heated rotors, but you could have more than one issue with the car. True story!
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