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1989 Volkswagen Rabbit Brake System losing pressure

Tiny
KARDOLF
  • MEMBER
  • 1989 VOLKSWAGEN RABBIT
  • 4 CYL
  • FWD
  • AUTOMATIC
  • 160,000 MILES
My daughters car - she tells me that she thinks she has brake problems. I get in, hit the pedal, and the thing goes straight to the floor. Resevoir is low, so I filled that. Looked underneath, and both rear wheels show fluid draining down the inside. Pull off the drum on one side, and I can see that the wheel cylinder is leaking. Bought one for each rear wheel, along with shoes and hardware kit, and put it all back together. Bleed the brakes (all 4 wheels, given how low the resevoir was), and the pedal still seems to travel farther than I would expect. Worse, when I hold the pedal down, it slowly sinks to the floor. Engine running or not seems to make no difference. Took it for a quick drive in the neighborhood. Fast, hard stop seems to work fine, and car quickly stops. Give myself time to slow down, and the brake pressure is gone before I can actually stop, and pedal is riding the floor.

Any ideas would be helpful.
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Wednesday, February 13th, 2008 AT 12:07 AM

4 Replies

Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
You can bleed it. Bench bleed the master by getting brass plugs and screw them into the two ports, then pump the master until you cant move the piston any more. Attach the lines, Have an aide press and hold the pedal crack the lines and retighten, repeat this till all air is removed at the lines, Don't let the master run dry, bleed rear cylinders by opening the bleeders and wait until the fluid dripps out. Close bleeders. Make sure the rears are properly adjusted, then test the pedal hieght.
If the master won't pump up and hold pressure replace it.
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Wednesday, February 13th, 2008 AT 8:17 AM
Tiny
KARDOLF
  • MEMBER
  • 2 POSTS
I did bleed the system (I think) - started at right rear, left rear, right front, left front, using a brake bleeder kit with a clear hose going into a little cup, watching for any sign of bubbles in the fluid. Had a friend helping me - close the valve, push down, open the valve, let up, repeat.

Is what you are suggesting a different process? I don't think I have heard of bench bleeding before. Since I still don't seem to have the pressure needed, should I just move to replacing the master?
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Wednesday, February 13th, 2008 AT 8:48 AM
Tiny
MERLIN2021
  • MECHANIC
  • 17,250 POSTS
If you install the brass plugs, if the master is no good you can pump all you want and won't get a pedal, if it's airbound, it will pump up, and you wont be able to push the pedal at all. Your choice, as far as replacing it.I would want to know first. Have someone crack the line as the pedal is held down, hear any air escaping? Thighten the line If so repeat this on both lines until all air is gone, bleed sequence is RR, LF, LR, RF.
This is a diagonal system and the pairs off the master are the same as the bleed sequence.
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Wednesday, February 13th, 2008 AT 8:59 AM
Tiny
COGNITO
  • MEMBER
  • 28 POSTS
If pushing the pedal hard seems to give you a higher pedal and pushing softly gives yuo a lower pedal then you probably have a primary cup not sealing in the master cylinder.I have seen this problem many times
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Friday, March 14th, 2008 AT 12:12 AM

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