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7 Series - E65 / E66 (2002 - 2008)
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  #1  
Old 09-20-2010, 11:37 AM
Beaug30 Beaug30 is offline
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Mein Auto: 05 745i
Hard brake pedal / cheaper fix

The most common cause of this seems to be the loss of vacuum in some way. The typically recommended repair is to replace the pump and the brake booster, as well as the check valve and vacuum line. Somewhere around $2k for those of us not under warranty. After a little research and back & forth with my mechanic, I inquired as to whether or not he has tested the pressure from the pump. After checking the pump pressure he found it to be at the appropriate level and we were therefore able to avert the replacement of the pump at a savings of $600. He did recommend replacing the o-ring where the pump is seated, and I did so. Now the brakes are fine and the only replaced parts were the vacuum line and the booster, and the o-ring.

I can expound more on this topic or would be happy to assist anyone having a similar issue.
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  #2  
Old 09-20-2010, 01:16 PM
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t_clealy t_clealy is offline
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Man...This exactly the problem I have right now. I have an 05 Li, I was driving while this happened about 2 weeks ago. All of a sudden I felt hard pedal and the car still glides when brake pedal applied. At the same time I've been warned by the light saying front brake lining need replacement. Then started ordering parts and sure enough b4 parts came in this happened. Now that I replaced the front pads already. The pedal still feels the same. Any heads up would be greatly appreciated.
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Old 09-20-2010, 01:32 PM
Beaug30 Beaug30 is offline
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brakes

At least you needed the pads anyway and did not replace only to still have a brake issue. The two (pads and hard pedal) are totally unrelated. What happened to mine was that a simple check valve in the vacuum line failed and therefore got oil in the booster and ruined it.

The system is set up as follows. (as I understand it)

Vacuum pump is attached to the block at the crankshaft and from there uses a vacuum line to connect to the brake booster. The booster accumulates pressure via the vacuum of the engine and then your brakes use this pressure in conjunction with the hydraulics to provide the power brake feel. The hard pedal is from a lack of either hydraulic or vacuum. In my case the vacuum pump o-ring failed and allowed oil into the vacuum system and therefore into the booster.

In order to check this you simply need to have the vacuum line removed from the booster and see if there is any oil in it. If there is oil then the booster is bad and possibly the pump, (needs to be checked for pressure)

No reason to get talked into a new pump if it is not needed. O-ring is a couple of bucks, pump is $350 ++

Good luck

(please note it is the o-ring that probably started a chain reaction and damaged the check valve. The oil from the o-ring failure is the likely culprit for nearly a $1000 repair. As a side bar, I believe an o-ring was also responsible for the space shuttle that blew up on take off.)

Last edited by Beaug30; 09-20-2010 at 01:39 PM.
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Old 09-20-2010, 02:28 PM
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t_clealy t_clealy is offline
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Thank you much for the responses. I will definitely look into it. Also Thanks for the heads-up. Will update later.
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