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02-11-2012 11:01 AM #1
Brake Problems - Binding, many parts replaced, booster???
My 89 635 CSi has had a continued brake problem for a couple of years now.
When the car/brakes are cold the brakes work fine. After about 20 minutes of driving (and braking) the front brakes are binding. The drivers side is much worse. Lots of heat obviously.
What happens after about 20 minutes is that the brake pedal develops about a 3/4 to one inch lash. No pressure at all as the pedal is applied for the 3/4 to inch distance then normal brake feel. NOT hard. I know this often points to the bomb and that was the first thing I replaced. NO improvement.
I have replaced:
the brake bomb - no improvement
replaced all the brake fluid - no improvement
front disc pads - no improvement
the front driver's caliper - no improvement
all brake hoses with high quality "racing" hoses - no improvement
I talked with a parts tech at one of our reputable suppliers and he now say that it may be the booster. He suggest taking the belt of the power steering/brake booster pump and driving the car to see if the problem developes. He say if it does not develope that this will point to booster.
Kinda makes sense but I want some feedback before I drive that car with no power assist brakes or steering.
I know the boosters are expensive.
If it is this problem is there an option for a rebuild booster?
Any other thing I should consider?
Has ANYONE had this problem?
Should I ask on another board like the 80's 5 series? How do I cross check the part for other series? (ATE 34331156925)
Thanks for the input!
02-11-2012 11:23 AM #2
- sciota, PA, United StatesMember No: 174051
- Join Date
- May 2009
- Rep Power
02-11-2012 04:56 PM #3
- Redwood City, CA,Member No: 165856
- Join Date
- Jun 2008
- Rep Power
The master cylinder sounds like a likely culprit.
While you've got the master cylinder out, you could consider replacing the seals in the booster. Check out these two links, as this guy sells the needed seals at a very reasonable price.
02-13-2012 09:58 PM #4
03-16-2012 10:52 AM #5
So here's the deal. It was the master cylinder. When the car is cold the aluminum housing of the master cylinder is contracted and thus the piston moves freely. As the engine heat warms the master cylinder housing the alloy expands. That expansion causes the master cylinder piston to bind and not release pressure to the front right and back right brake (but it did affect all brakes from time to time).
Drain the fluid reservoir housing and remove it by pulling upwards. Do this BEFORE removing the master cylinder. The master cylinder will have to be tipped and lines will have to be moved slightly (especially with ABS) to get the cylinder it out. Install the master cylinder without the reservoir because of the tipping during the installation process.
I would recommend, "bench bleeding" the new master cylinder on the car. Just use the bench bleeding "plugs" and tubes provided. You may need longer tubes so they will feed back into the fluid reservoir housing. Just fill the reservoir with proper fluid and recirculate the fluid thru the master cylinder, thru the tubes, and back into the reservoir.
If this is done the calipers will NOT have to be bleed. Any small amounts of air will percolate back up into the reservoir when the car is at rest.
Also, there appears to be a slight variation among the master cylinders. Some use a sleeve that is attached to the master cylinder to guide and seal the master cylinder to the brake booster housing. Some use a rubber O ring. Understand that there is NO fluid in this joint so getting a perfect seal is not required. Of particular note, the rubber O ring WILL NOT WORK with the guide sleeve master cylinder type. The ring will only crush and not allow the two to mate properly. Don't worry tho because the sleeve will me more than adequate to keep dust out.
Good luck. And I hope this helps.
04-11-2012 10:14 AM #6
- Orange, California, USAMember No: 184053
- Join Date
- Nov 2010
- Rep Power
Here is further evidience that it is the M/C.
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