passat 99 tdi estate sinking brake pedal

[passat cruiser]

hi there

had a brake failure on this car brake pedal went to floor and lost all brake fluid.

so had master cylinder replaced as seals gone and rear brake hoses as they were seeping at crimped end

pressure bleed the complete system and car has working brakes


but pedal still sinks to the floor if you hold constant pressure on the pedal
with the engine running

engine off and pedal is hard and does not sink at all

any ideas people

[martin1810]

Are you losing any fluid now. The only difference with the engine running is the servo. This often makes the pedal sink a bit, but not all the way to the floor. You only have a few choices.
1. You've got a fluid leak.
2. The new master cylinder is faulty
3. The servo is faulty.

[passat cruiser]

thanks for reply,

not losing fluid now and no leaks on any of the pipes, hoses etc no calipers sticking etc
well the test for the master cylinder is that you turn off ur engine and if pedal is solid then nothing wrong there
its only when i run engine i have a problem with pedal creeping

i had read up that u have to bleed the brakes with vag.com to get air out of abs pump is this true?????
though this might be problem as i dont have vag com so cant do it that way

[martin1810]

If it's air the pedal will sink under any conditions and will pump up. You don't need vag-com but it might be worth bleeding the brakes with the engine running. Your description doesn't sound like air in the system. Is there any chance that it's the wrong master cylinder.