[Vwdiesel] Weird brakes

[Doyt W. Echelberger]

At 04:09 PM 1/2/2008, you wrote:
>My brother is having an odd problem on his rabbit, and I don't know what to
>tell him.

....................Hello Eric......I just ended 4 months of experimenting 
with the same problem on a 1985 Jetta TD that I have owned for about 20 
years. Jettas are a lot like Rabbits.  I'll tell you how I fixed it, 
although the tale is flavored with sad and peppered with frustration. And 
it will be up to you what you say to your brother.


>His brakes will work fine for anywhere from 20-50 miles, but then slowly
>build up pressure until the car wants to stop. If he opens the two nozzles
>on the sides of the master cylinder the pressure releases and is then fine
>again for a while. This happens over and over. He recently put a new master
>cylinder and one new brake line on the car, and afterwards is when this
>started.
>My opinion is that the new master cylinder is somehow faulty, but I really
>don't know. This is a strange one that I haven't seen before. Does anyone
>else out there have any ideas?
>
>Thanks!
>Erik
 >>>>>>>>>>>>

.......................................I actually replaced the MC twice, 
following the same logic and able to claim they sent a bad one the first 
time.  Problem persisted.

Next, I replaced both front calipers.  Pressure build-up problem remained.

I replaced all the flexible brake hoses. Problem not solved.

All that remained was the vacuum booster....dish shaped unit bolted to the 
firewall.

I Inspected the vacuum booster carefully by feeling every surface with my 
fingertips.....and found extensive rust and corrosion on the back surface 
of the dish. Big flaky crusts of rust. There was some evidence that the 
vacuum booster wasn't holding a vacuum....leak-down test failed when I 
threw a pressure tester  on the system, after disconnecting the hose 
between the booster and the vacuum pump (device mounted where dizzy usually 
goes in a gasser.)

I then looked carefully at the cabin-end, where the rod from the brake 
pedal enters the vacuum booster. Noticed that the rod had disturbed the 
features surrounding the booster back door. Rod had been removed during 
both replacements of MC.

To the punch line....I replaced the vacuum booster unit and the pressure 
build-up problem ceased to exist.

This was all very expensive experimentation.  I also think that I 
discovered it is possible to damage both the vacuum booster and the MC 
seals by irreverent manipulation of the actuator rod as it is taken out and 
put back in.

And I clearly remember being amazed by the only thing that released the 
build-up during the first few months of experimentation....loosening a hard 
line connector on an outlet of the MC and letting the pressure push out 
some brake fluid.

There...you have read my tale of frustration and wallet-thinning 
experimentation, and you need to consider and use the information in better 
ways than I did and perhaps tell me if any of it was helpful. And I can't 
guarantee that replacing the vacuum booster will fix your problem, or can I 
know if you or someone else has damaged both units by messing with the 
actuator rod.

Peace, fellow traveler,

Doyt