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Suspension & Braking Forum by BimmerWorld
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Old 12-26-2009, 07:09 PM   #1
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Join Date: Dec 2009
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My Ride: 2004 325XiT
Question Strange braking behavior - need to "double-brake" to get full braking power

I am new to this forum and don't do my own work, but I own a 2004 325 XiT with 50k miles on it that has been taken care of meticulously.

I am experiencing a strange braking behavior from my car. When I first press down on the pedal, it sinks in just lightly lower than normal and the braking is there but not OEM-strong. When I release the brake pedal and immediately apply the brakes again, the pedal sinks in less and the full braking power comes back. The difference is amount of pedal sink is very slight, but noticeable to me and the difference in braking power is easily noticeable. I had all 4 brakes done earlier this year (new rotors, new pads) and the service records show that the brake fluid was replaced and the lines were properly bled. When the brakes were new, there was good braking power and this behavior was not noticeable. However, as the brakes wore in a bit, this behavior became noticeable. I have had 3 different shops (including a dealer) look at my car and they all told me there doesn't seem to be anything wrong (rotors, pads, calipers). I am now turning my suspicion to the master cylinder, but really have no clue.

Has anyone had similar problems? How could something like this be investigated or solved? Is it even a problem to be concerned about?
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Old 12-26-2009, 08:43 PM   #2
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i would try changing the brake fluid again
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Old 12-26-2009, 09:27 PM   #3
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Changing the brake fluid and flushing/bleeding the lines was thought about, but here's a bit more detail about the history of this behavior that may or may not lend support to the suggestion. When the brakes were done on the car earlier this year, I first had the rear brakes done. They did not change the brake fluids. After a few days, this double-braking problem appeared. Thinking that maybe the front brakes were going, I had the bront brakes done. This time around, I mentioned the double-braking behavior and the shop suggested fluid replacements. So along with front brake replacement, the brake fluid was replaced and bled. All seemed good until few weeks later, the behavior returned. Eventually, I found that the front rotors were "warped" and the shop that did the front brakes turned the rotors. After that, it seemed good until few weeks later, the behavior returned yet again. I don't know what to make of these sequence of events.
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Old 12-26-2009, 09:31 PM   #4
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Sounds like air in the line, a bleeding would probably work, it is possible that the tech left one of the bleeding screws a fraction loose and it has taken this long for air to be induced into your line. Bleed first cause it is the cheapest easiest this to do.

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brake, master, pedal, sink, weak

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