Spongey brakes! Not again!

[RossyB108]

Hi,

I fitted new rear brake lines and a master cylinder a couple of months ago because I was getting spongy brakes (and my pipes were very corroded). They've been really good since, until...

About a week ago my brakes started getting a little spongy at the first press again. It's quickly got worse until now my foot nearly reaches the floor.

If I press the brakes and straight away press them again, the brakes are hard and normal but after about 5 seconds or so of not braking they are spongy again!

I'm guessing I've got air in the system but can't understand why it would suddenly happen again after a good 6 weeks of them being fine (since the new parts) and also get worse so quickly too

I can't see any signs of a leak, but the only other thing to note (which is probably nothing), there's a wierd noise that comes from the rear near side corner when I take my foot off the brake quickly - a bit like a minature donkey being run over - which stops as soon as the brakes up, I'm wondering if it's air in the bias valve coz I know that's around that area.

Sorry to waffle, wanted to get the detail in - hope someone has experienced this before and knows what it is, I can't keep throwing £ at it to find it's not resolved!

Thanks!

[Wayne]

Could be air trapped in the rear calipers, try bleeding it through again.

[Dolly]

i had problem with a mk2 the once, kept bleeding it but had a crap brake pedal, found i had a slightly sticking calliper which must of been holding the air. might be worth pushing back the front and winding back the rear callipers so all the pistons are totally in.

and to do with your other post you can put a higher spec brake fluid in the system but its not going to help unless your doing trackdays and alike (youll overheat the brake pads and get fade before your brake fluid boils) but if you do make sure all the old stuff is pushed out. you shouldnt have 2 different types in the pipes i dont think it mixes well!.

[Benrevs]

Check that the brake bias valve is all in good order, they are prone to seizing and leaking etc. Always worth changing as once they are fooked... they are fooked.

[RossyB108]

Thanks for the replies. Got my brakes bled at the garage today, feel spot on now - I'll keep an eye and report back if I get the dreaded sponge back again...

[RossyB108]

Ok, my brakes have gone again.

They slowly got worse over the last couple of weeks and this weekend really got quickly worse.

I'm not far off hitting the floor when I brake the first time, after pumping the pedal acouple o ftimes they are ok. can't understand it.

The donkey is still there too.

I did also notice that is I pump the brakes a couple of time so they are firm, if I hold my foot on the brake it very very slowly pushes to the floor, barely noticable at first.

[clipperjay]

You have a leak somewhere getting worse by the sounds of it.
You need to look for sweating on any unions and bias valves could be just the brake pipe unions where the flared nut was loose or not flared enough to hold true on the nuts?

[RossyB108]

I've had a good look and can't find any evidence of a leak, and the level of fluid never goes down

[Wayne]

Could be a master cylinder problem

[AudiA8Quattro]

Try jacking up the rear end, supporting on stands, get the back up as high as you can.
Clamp the rear brake regulator valve, pump the pedal about 20 times.
Leave the car overnight, and bleed the rears.
Quite often the air seems to settle in the rear of the system.