Is this possible?
 

Hi my friend has a 2004 Passat. He had it in the dealer for some work and they said he needed new rear brakes and the system should be bled. They quoted him $650.00. We replaced the brake pads and I pumped the brakes to firm everything up. Then we were going to bleed the system and add new fluid. With the engine off I had my foot on the pedal (with really just the weight of my foot with no pumping) and he loosened the bleeder valve and no fluid came out. So we tried the other side thinking something might be wrong with the one and same thing no brake fluid came out. So we decided to forget about bleeding the brakes. When we started the car up the brakes worked fine, but if you stopped and kept your foot on the brake pedal your foot would slowly go to the floor. Like the master cyclinder went bad. We tried bleeding the brakes again with the motor running this time and fluid came out. My question is. Is it possible to damage the master cyclinder by trying to bleed the brakes without the motor running? In the past I have always bled brakes without the motor running.
Thank You

i wouldnt think so.

but i have no experience with vws.

did he get a quote from the dealer saying what they were going to do? and did you do that instead?

tom w

It has often been my observation that when bleeding a brake system, the master cylinder will fail on older vehicles.
This is due to the silt build up in the reservoir...a combination of oxydized fluid and rust from the systems internals.
Mercedes seem prone to this too.

VW does this a lot if the vehicle is 6 years old or more.
To stop/reduce this happening I now remove the reservoir and flush it out...refit and fill with clean fluid.

The 'slow' sinking of the pedal is the hardening of the umberella cup seals and then being hard, the washed down debris from the bleeeding score the cup seal lips....some times you can stamp the brakes real hard and quickly, and then get a firm pedal...this confirms bad cup seals.

VW Passat: Rear brake pads, instal/parts...$165.00.
If the car is ABS equipped you need to activate the ABS pump.

However...NEVER push back the fluid by retracting the caliper piston/s with out bleeding the fluid out through the bleeder as the old fluid can and will cause problems in the ABS unit.

Reverse flushing the ABS has killed many systems.


.

.

Check the TDI forum. I think I recall reading something about bleeding the brakes using the diagnostic computer to control the ABS pump.

Thanks Guys. What is TDI forum?

http://www.tdiclub.com/




.

dkveuro,
thanks for the tip about pushing the calipers back. i have always done this but probably not any of my cars so far have had abs. i will try to keep this in mind. cleaning the res sounds like good insurance too. i often suck them out with the baster, but that wouldnt get it all would it? is there a low area in the res that will collect debris and never empty fully?

tom w

Tom...the res' has two chambers and the front one on the 123/126 etc is difficult to clean. I use a Water Pick in the shop bathroom to clean it out...have used hard rice in stubbon dirty res' to knock loose dirt....also with a few drops of Dawn or liquid Tide.....shake it like crazy and do over a couple of times.
....... blow dry with shop air and rinse out twice or more with brake fluid your going to use, to absorb the H2O....you'll know when it's clean.:)
Alternative is to buy a new res'....they come high$ with two float units per.

Mech' to owner some time later .." I think I found your brake problem sir..."
Owner.." Oh? What did you find."
Mech' .." Seems your car was owned by Asian people:chinese2: in the past ":D ....holding up rice grain.




.



.


.