Help needed Brake problem

[sacha35]

Hi guys hope you can help, this one has got me baffled.


Audi A4 B8 2.0 TDI S-line 2008.

Ok Changed out the front and rear pads over the weekend and now I have a soft brake pedal that travels to the floor, at first I though air might have got into the system somehow so used my easy bleed and flushed the system out but know change.


When engine is not running the brake peal is hard with no movement at all even with a good amount of pressure on the pedal, but when engine is running the pedal is soft and will travel to the floor. My first thoughts are master cylinder but how can the brake peal be hard with no movement t all when engine is off ? but when engine is running the pedal is like a wet sponge.

I would be most grateful if you can help in this matter as I have MOT due soon and nee to fix the problem.

Also if you think it is the master cylinder where is the best place to get one?

Thanks again in advance.

[sacha35]

Bump

Anyone have any ideas ?

[zollaf]

when you pushed the caliper pistons back, did you undo the bleed nipples to let the old fluid out, or did you push the old fluid back through the system. ?

[sacha35]

when you pushed the caliper pistons back, did you undo the bleed nipples to let the old fluid out, or did you push the old fluid back through the system. ?

Hi Zollaf

Thanks for your reply
lid removed then open up bleed valves then epb open with pc and pads changed out , rear pads closed with PC.

What I don't understand is pedal is right at the top and rock hard without engine running, if master cylinder (http://go.redirectingat.com/?id=14101X710282&xs=2&url=http%3A%2F%2Fshop.ebay.co.uk%2F%3F_nkw%3Dmaste r%2Bcylinder&xguid=1958e1c370d88f5bcb55e660771230dd&isjs=1&xword=master%20cylinder&xcreo=300003&xpid=773188&xed=0&sref=http%3A%2F%2Fwww.vwaudiforum.co.uk%2Fforum%2F showthread.php%3F162349-Help-needed-Brake-problem&pref=http%3A%2F%2Fwww.vwaudiforum.co.uk%2Fforum%2F forumdisplay.php%3F201-Audi-A4-B8-Forum-2008&xtz=0) or caliper seal had gone then the pedal would be soft all the time ? but as soon as the engine is started pedal is soft and slowly drops to the floor.

[zollaf]

with engine running you have servo assistance. no engine means no servo so pedal will always be rock hard. you either have some air still trapped or you need a new master cylinder. with engine running, can you quickly pump the pedal to get a firm pedal.

[sacha35]

with engine running you have servo assistance. no engine means no servo so pedal will always be rock hard. you either have some air still trapped or you need a new master cylinder. with engine running, can you quickly pump the pedal to get a firm pedal.

Just tried what you said, the pedal comes up to the top when pumped quickly but as soon as I stop pumping the pedal slowly drops and goes down.

Do you think I have air in the system still or does this sound like MS has gone.

Thanks again for your help.

[zollaf]

i would o for a test drive. sometimes a test drive sorts these problems out.
in fact i had a beetle in yesterday. we had to disconnect the rear brakes to do the axle bushes. put it back together and just couldnt get a good pedal, soft and sinking. no fluid had been lost and in fact no air came out when bled. started to panic, so took it out and straight away the pedal came good.

[sacha35]

i would o for a test drive. sometimes a test drive sorts these problems out.
in fact i had a beetle in yesterday. we had to disconnect the rear brakes to do the axle bushes. put it back together and just couldnt get a good pedal, soft and sinking. no fluid had been lost and in fact no air came out when bled. started to panic, so took it out and straight away the pedal came good.

Thanks for advice

The car stops great and little pressure needed to stop the car, if i slam on the brakes the ABS kicks in and the car stops immediately with screeching of the tyres, its just the pedal travel that is the problem. As stated when brake pedal is pushed with engine running it will slowly travel towards the floor like a leak is present but there is no leaks, the pedal does not go right to the floor but from the top when pushed it will slowly travel about two or three inches, I have bleed the system again with no change in the pedal problem and am starting to think the first stage seal has gone in the master cylinder.

What do you think ? air still in the lines or master cylinder.

[zollaf]

eah, probably the master cylinder seal. to be fair, most diesels will sink like this when you press stationary. you are in fact usually using enough force to lock the wheels though, with a 10 ton trailer behind, due to the amount of servo assistance, so there might actually not be a problem, as long as the brakes are working properly which they are. it may just be the pads need bedding in, especially if the discs are slightly worn or have a slight lip. if you are happy they are performing as they should then i would give it a good few miles to let the pads cut in before condemning anything.

[Alan02]

Check you dont have a "lip" on the edges of the discs! Pads will need bedding-in till they wear to suit the disc. This always causes a soft pedal, extra travel with new pads.

[sacha35]

Thanks for the info guys, tried pressure bleed once again but still the same sort of peal travel, I have done around 300 miles on the new pads now so It is looking like MS has gone :( so will be changing it out. Where would you recommend to look for a new MS, the one I need is 8K0611021B ?

Thanks again for all your help