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-   -   Brake pedal slowly goes to floor (http://www.bimmerfest.com/forums/showthread.php?t=563670)

Dani G 08-23-2011 02:44 PM

Brake pedal slowly goes to floor
 
1986 535i

Your first thought will be Master cylinder. I replaced it with a used part off another car, still had the same issue, then bought a new one and it hasn't changed the problem. (300$ down the drain)

Symptoms:
With the car running the pedal slowly, with substantial force, creeps to the floor.

I do get braking power, but not 100%.

With the car off, they are hard.

I have pressure bled them several times. 2-3

The fluid level does not drop, even after putting the pedal to the floor 20 times. So no leaks.

We thought maybe there was a flex line that was flexing but I could not feel any bubbles while the pedal was pressed. I will attempt to pinch them with some Vise-Grips on the car side to double check.

Questions:

My manual does not specify a bleeding method for the MC. Is there one? Could this be the issue even after having pressure bled the system?

Could my Hydro boost be applying too much pressure to the MC and overcoming the seals? Otherwise I can't see how this system could affect it.

Any other thoughts?

I am desperate as I need this car on the road ASAP.

catso 08-24-2011 07:04 AM

That usually indicates air in the system. Bleed the brake fluid from each wheel with a clear piece of tubing into a jar so you can clearly see when the bubbles stop. You will probably have to go around the car a few times. Start with the RR, LR, RF and lastly LR. Leaving the bleed screws open overnight to "gravity bleed" the system might also be helpful.

alichak 06-25-2014 08:27 PM

Quote:

Originally Posted by Dani G (Post 6274408)
1986 535i

Your first thought will be Master cylinder. I replaced it with a used part off another car, still had the same issue, then bought a new one and it hasn't changed the problem. (300$ down the drain)

Symptoms:
With the car running the pedal slowly, with substantial force, creeps to the floor.

I do get braking power, but not 100%.

With the car off, they are hard.

I have pressure bled them several times. 2-3

The fluid level does not drop, even after putting the pedal to the floor 20 times. So no leaks.

We thought maybe there was a flex line that was flexing but I could not feel any bubbles while the pedal was pressed. I will attempt to pinch them with some Vise-Grips on the car side to double check.

Questions:

My manual does not specify a bleeding method for the MC. Is there one? Could this be the issue even after having pressure bled the system?

Could my Hydro boost be applying too much pressure to the MC and overcoming the seals? Otherwise I can't see how this system could affect it.

Any other thoughts?

I am desperate as I need this car on the road ASAP.


I have the exact same problem after replacing brake pad and rotor and calipers, needless to say after professionally done brake bleeding! I thought I had some air in the ABS system, so went to an indie to do a proper bleeding with ABS activation....which he did, but didn't fix my problem.

IF you figured out what was wrong, please let me know. I'm about to drain 300$ down the toilet and buy a new master cylinder!

south26 06-26-2014 01:47 PM

I have a good used brake master for 50 shipped.


Andy

BMWFatherFigure 07-01-2014 07:44 PM

Pedal creep can be an internal leak in the MC between the chambers. That would be my first thought. That will nott show any fluid loss. Bleeding the ABS unit is a bit of a 'black art'. I would consult a good brake specialist for that. Creep is not usually air in the system - that is just a 'spongy or springy' feel with consistant movement. It is not possible for the booster or servo to over presurise.

alichak 07-20-2014 01:18 PM

Quote:

Originally Posted by south26 (Post 8426960)
I have a good used brake master for 50 shipped.


Andy

thanks for letting me know. will be in touch if I figure out it is the problem.:thumbup:


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