Brakes playing up.

If i push my brake pedal it feels good and solid and stays put. With no sinking l

My brake sinks when i hold it in and turn the engine on as you would expect with servo kicking in


How ever what has me puzzled is when engines running and i push and hold the brake it goes firm and then starts to sink.

Where to look- servo- master cylinder - drum adjustment ?

Nothing is leaking that i can see and i dont seem to be losing fluid. Its a whole new system with refurbed calipers , except for servo- master cylinder and vac pump.

Any ideas ?

Given everything you've done/replaced, sounds like a leak past the seal in the master cylinder. That's where I would start.

Moi aussi except wouldnt it do it with the engine off as well as on ?

It only sinks when the engine is running, good and solid when its off...

Isn't that what servo assistance does? I could be wrong but most the cars I've driven do this at a standstill. How does it feel on the road?

top drive said:

Moi aussi except wouldnt it do it with the engine off as well as on ?

It only sinks when the engine is running, good and solid when its off...

Click to expand...

Probably the extra pressure on the cylinder, created by the servo assist, is enough to cause the seal to leak. When you are just using your foot, with the engine off, you might not be pushing hard enough. You may think you are pushing hard enough but, compared to having the servo helping, you probably aren't. It doesn't feel right when you are pressing hard on a brake pedal when the engine's not running, you feel as though you are about to snap something, so you may be being more cautious than you think.

Feck it , a master cylinder rebuild kit is about 5 quid and i couldnt get an mot at my local til the 15th june so i have time

None of my other cars do this so somethings not right . Although googling and searching the forum shows others with the same issue have found a new master cylinder hasnt solved it.

top drive said:

Feck it , a master cylinder rebuild kit is about 5 quid and i couldnt get an mot at my local til the 15th june so i have time

None of my other cars do this so somethings not right . Although googling and searching the forum shows others with the same issue have found a new master cylinder hasnt solved it.

Click to expand...

Well, maybe they've got leaks somewhere else then. There's no reason why it couldn't be a master cylinder problem in your case.

I had a similar issue with mine which I found to be master cylinder seals. No loss of fluid as it's just leaking internally. Rebuilt the master cylinder and problem solved

Ok m/c kit in my basket