Another Spongy Brakes question - Zafira

Assuming you have assembled it all properly ?? and you haven't got a flexi with a bulge in it.

Usual reason this happens is:

If the system has not had its proper fluid changes (every two years at least) water builds up in the bottom of the master cylinder and rusts/corrodes away a small area. When new pads are fitted or the pedal is pushed beyond its NORMAL range of travel, the seals are pushed over this rough bit and are damaged enough to give a poor feel to the pedal (usually because the dual action master cylinder is now single)

When ever I change pads now I always pump the pedal up using tiny presses so that this does not happen, as I have come across it several times over the years.

Only cure is a new master cylinder.

Mrcheerful

you should always bleed your brakes after changing pads , new pads sometimes feel slightly spongy until they are bedded in

Care to explain why? Only I've been changing pads on cars from when disc brakes were first becoming common. I've *never* bled them afterwards. I've

Chris

Hmm.

When i pump the breaks and leave the pressure on the peddle it does not slowly descend, it remains firm. Wouldn't it lose pressure and slowly sink if the master cylinder was damaged?

Not as long as one half of the dual master cylinder is still ok.

You can usually tell if the master is the problem, as you press the pedal down can you feel a subtle clonk in the pedal as the second half is pushed? (it is usually pressed hydraulically internally, but when the seals are damaged it gets pushed mechanically) If so then there is either air in the system (unlikely if it was ok before or the seals are letting fluid past internally.

I notice you don't comment on whether the brake fluid has been changed by the book.

To eliminate whether you have dome something wrong on the front brakes: clamp the flexis (preferably with the correct clamp or carefully use mole grips) each side and see whether the pedal feels right, if it does remove each clamp in turn and see what the pedal feels like with only one brake operating, this may show up which side or whether both are equally a problem.

Mrcheerful

I haven't touched the brake fluid resevoir as it was just under the MAX level. I reckon that once I get this sorted I'll replace the brake fluid as it's probably been in the car since new.

Things appear to have taken a turn for the worse overnight, today the foot peddle will sink slowly if I apply pressure and leave it applied.

I'll try that clamping trick you suggested....

Thanks again.

Did my Zaf front brakes this weekend as well. HBOL does warn that in some cases the master cylinder seals have been known to fail due to pushing back the pistons. I suspect that is your problem.

Mind you mine are now as squeeky as hell. I spose i'll have them apart again this weekend to apply the copperslip.

Paul

I stripped and rebuilt the brakes again then completely flushed all the old brake fluid out and replaced it with new stuff, no more spongy brakes and it passed the MOT at 3pm today :-)

Thanks to everyone that replied.