Sinking brake pedal

[muddyboots]

Over the weekend I noticed the following on the Passat:

- With the engine running and servo assistance, if I press HARD on the brake pedal it sinks slowly but steadily, it will go all the way to the floor if I try for long enough (guessing around 10-15secs).
- With the engine off and vacuum exhausted, I can stand on the brake pedal and I can't feel any movement.

I can't see any fluid leaks and the fluid level seems fine, doesn't seem to be dropping.

It's probably done this ever since I had it, but I changed the pads/discs on Friday and noticed it when I pressed the pedal hard to settle the pads before driving off.

Any ideas ?

 

[cheshire cat]

Lee had this on the Terrano, turned out to be a microscopic leak on the rear cylinder, no other contamination!! try clamping each flexi in turn, if not sounds like master cyl' cheers Nic

 

[TheOtherSimon]

I had it on my old golf, turned out to be the servo. The giveaway is that it's fine when the engine is off.

The other thing it can be in the bit of plastic that connects the pedal to the servo.

Simon.

 

[muddyboots]

Lee had this on the Terrano, turned out to be a microscopic leak on the rear cylinder, no other contamination!! try clamping each flexi in turn, if not sounds like master cyl' cheers Nic

Nic -> Understand what you're saying, but do you reckon a hose clamp would resist the high pressure generated by standing on the brake pedal ? I'd have though fluid would still get past the clamp.

Simon -> Servo feels like it's generating assistance OK, pedal is firm with no engine then sinks down as you'd expect it to when engine is started.
Maybe without the engine running and no servo assistance, my leg isn't strong enough to cause the sinking.

I can't see how it will help, but I'll bleed the ABS unit with vag-com then pressure bleed new fluid through, you never know !

 

[cheshire cat]

worth a tyr if you have a good qhality pipe squeeze tool, no moles!!

 

[bluenose]

Over the weekend I noticed the following on the Passat:

- With the engine running and servo assistance, if I press HARD on the brake pedal it sinks slowly but steadily, it will go all the way to the floor if I try for long enough (guessing around 10-15secs).
- With the engine off and vacuum exhausted, I can stand on the brake pedal and I can't feel any movement.

I can't see any fluid leaks and the fluid level seems fine, doesn't seem to be dropping.

It's probably done this ever since I had it, but I changed the pads/discs on Friday and noticed it when I pressed the pedal hard to settle the pads before driving off.

Any ideas ?

I've got the same problem on my mk2 Ibiza and was wondering if you found out what was wrong?
I have just renewed the brake fluid in mine (the old fashioned "pump the pedal" method) and have been told that the seals in the master cylinder could now be damaged.
Could that explain the pedal movement with no fluid loss, as the fluid is forced past the seals?
Thanks in advance for any info.

 

[silver surfer]

most diesels do that because a pump provides the vacuum for the servo we have to be careful on mot no to fail what is just a common action