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Old 05-13-2010, 11:59 AM   #1
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Question Strange brake pedal feel

Recently the effort required to brake increased significantly. I can still engage the ABS during lapping but I have to push hard the brake pedal.

I have a BMW 330ci 2002 that I use for lapping. It is also my daily driver.

The last two years I was using Hawk HP Plus pads with very good result (Except the dust). This year I had to change my pads and again I went with the HP+. I did about 500mi with my car after having changed the pads.

At the first track day (after 5 months of winter break) I started slowly and gradually increased braking power.

However I noticed a strange pedal "feel". During the first lap the braking power is outstanding. Meaning that with a little pedal effort the car slows down very well. However at the second lap I have to push very strong the pedal in order to slow down my BMW and occasionally engage the ABS.

My brake fluid is new and there is no air.

Can this problem come from my master cylinder worn out ?
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Old 05-13-2010, 12:01 PM   #2
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check the brake booster and vacume lines.

1999 328i Sport Package, Premium Package, 5 speed, Alpine white.
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Old 05-13-2010, 01:39 PM   #3
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Ah yes, I didn't think about ...
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Old 05-13-2010, 05:03 PM   #4
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I think your pads are glazed. I'd recommend having the rotors turned, pads sanded, and then you may as well flush the brake fluid at the same time.

With that said, the HP Plus pads are not sufficient past intro-lapping and just plain won't work for some people's driving styles. Consider switching to a Performance Friction "New Z-Rated" Pad if you want a hybrid pad.

If you are ready to start swapping pads and rotors for the track and street then consider ordering up a second set of rotors and some Carbotech XP12/XP10 pads or some Performance Friction 01/06 compound pads.
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Old 05-13-2010, 08:17 PM   #5
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An easy way to check the vacuum booster is this:

Start the car and let it run for about a minute. Rev it up a few times.
Let the car sit for 30 minutes.
Pull off the hose leading to the booster (where the check valve goes into the booster)
If you hear a big sucking sound while removing it, then you know that your booster and check valve are fine and that Ross Perot was actually talking about BMW brake boosters.

Brake boosters are required to work for 5 normal stops if the engine quits while you are driving.
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Old 05-16-2010, 08:10 PM   #6
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I checked the vacuum and it is perfect.

I did more than 400mi lapping over this week-end. My brakes are working now. It was some dirt on the rotors ... (even maybe a little grease ?!). Actually I cleaned my rotors, wheels and tires with soap and high pressure water after the first lapping day. Next days things were working properly.

Thanks for the pad advise. This is something that I was thinging about for next year. I can still outbrake many cars with my setup. I am a very late braker
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