New master cylinder fitted , very soft pedal to floor

[guyzza75]

After suspecting a bad master cylinder, I bit the bullet and got a new one and changed it over (hell of a job). Anyway new MC fitted filled up with brake fluid and proceeded to bleed the brakes etc ..furthest away and in proper sequence. I have used litres of fluid and getting a steady flow of fluid out of all the nipples with no air. I have also run VCDS to purge the ABS pump etc and yet cannot get a stiff pedal when engine running. Pedal goes nearly to the floor. Suspecting a dodgy new master cylinder I placed my old one back on as at least I had a pedal and yet exactly the same issue now with that one. I have spent a fortune now and used three complete days trying to sort this but with no luck. I have bled the two lines coming from the master cylinder also and still nothing...can anyone help please?? Before a hammer goes through the windscreen ... a4 b7 2.0 tdi 2005 sline ..thanks

 

[vag-tech]

Does the master cylinder itself have bleed screws? If so it’ll need bled too.

 

[NHN]

Sounds like air pockets, its a **** job tbh.

 

[vag-tech]

its a **** job tbh.

Not done one for a while I’m pleased to say...this’ll be the one with the torx that secures the reservoir faces into the body...? ‍

 

[guyzza75]

Thanks for replies ..no the MC has no bleeding ports and I primed as best I could. I have run the ABS pump via VCDS and followed the procedure but still spongy brake ! ...dam Audi

 

[vag-tech]

Thanks for replies ..no the MC has no bleeding ports and I primed as best I could. I have run the ABS pump via VCDS and followed the procedure but still spongy brake ! ...dam Audi

Did you use a pressure bleeder?

 

[guyzza75]

Yes used a bleeder which connects to tyre at 20 psi..also used a one way bleeder on two wheels at a time I am racking my brain.. it's really weird, fluid out of all wheels with no air bubbles and used about 4 litres or more of fluid

 

[vag-tech]

Mechanical parking brake?

 

[Blurtar]

I feel your stress! I had this last week on exactly same spec as your car. I replaced all four brake flexis on my Avant along with new cunifer tails on the front calipers and a joint to make on a seized union on the rear.

All went quite well until bleeding the brakes. Used a pressure bleeder on the correct sequence rear to front. Went round twice and still spongy.

Reverted to the pedal method and they improved slightly but still spongy. Don’t ask what happened as I can’t explain it but the brake pedal came back after a bleeding sequence with engine idling.

The pedal is now back the same as before if not slightly better. I also noticed once the engine was idling I got a load of discoloured fluid from the N/S/F caliper.

I’m aware it’s not recommended to bleed with the engine running due to the servo been in operation but I was frustrated and out of ideas.

Worked for me and nearly did a jig!

 

[guyzza75]

Thanks Blutar
I will give that a go. I also spoke to my local ex Audi fitter and he suggested bleeding with engine running thanks for the reply

 

[guyzza75]

Update to this thread ..I have bled the brakes to death and change all pads etc.. I think I cracked it !! ...it appears that where the brake pedal joins the master cylinder there is a long thread with a locking nut and I didn't take up the slack and bring the brake pedal up far enough, therefore when pressing the pedal there was a lot of play and then a hard pedal an inch or so from the floor. It's a pain in the backside to get to and you have to remove the brake pedal switch everytime you adjust. So if you change a master cylinder and the brakes are just biting at the bottom try this. You will need to remove the panel under steering column (3 x 8mm bolts - 1 is hidden in the fuse bay) then all is required is a 19mm short spanner and a 16mm spanner (the lock nut is 19mm and the bar with thread is 16mm. To get the brake light switch out you need to puch the end of the switch in and wiggle back and forth and turn anti clockwise. I can't stress enough do not try and force it to turn as it will break! (From experience)....when you have undone the lock nut turn the threaded bar and you will see the brake pedal rising higher or lower ....hope this helps

 

[guyzza75]

Forgot to mention that the brake switch readjust everytime you move it ..if you don't remove it you will get a brake light on dash and ABS light..once out adjust the bar and put the brake switch back in last when adjusted