CO AVANT

So I installed a new brake master cylinder without a hitch (ATE brand just like stock). Bled brakes and slave cylinder twice. Start the car and brake pedal goes to the floor. The rod that goes through the brake booster is in the master cylinder piston so that's not the problem. I even installed my old master cylinder and re-bled. Same issue. Brake pedal goes down to the floor. I did exactly per Bentley manual and now have zero brake pedal force. Pedal goes to the floor with hardly any effort so the brake booster vac is still working properly. I can get pedal force with the car off if I pump on the brakes, but the moment I turn the car on the braking force is gone and the pedal goes down to the floor. No leaks, all lines are tight. The only test for abs pump I can do is the output test in vag with cycles the pump (you can hear it when it turns on). So why the hell am I not getting any brake pedal force anymore? I know it's not the MC causing this. Only thing that comes to mind is the hydraulic control unit or ABS controller/pump... if it was a booster issue the pedal would be hard as a rock, not easily dropping to the floor. anyone have any idea??? This is driving me nucking futs

Merkin

did you bleed the clutch too?

CO AVANT

wondering if I have air in the hydraulic controller itself or what. Wierd thing is I can pump up the brakes to stiff with the car off but once I start the car that pedal force releases and the pedal falls to the floor again.

Merkin

maybe try to bleed with the car on

QuattroFan02

At what PSI did you bleed?

CO AVANT

20-25 on brakes, 37 on clutch slave. I get brake firmess with car off, but goes to mush with car on

CO AVANT

Tried, no go.

520

don't use the pressure bleeder this time. But why did you replace the MC at 1st place?

CO AVANT

I tried 03 ABS - basic settings block 001 and 002 and they don't have on/off functions to bleed the system. Must be different from ross-tech procedure. I could get the abs controller to turn on by using output tests.... that is all though. Replaced cause wasn't getting brake firmness until pedal was 1/2 way pressed in.

520

Was the rest of your braking system in top shape when the pedal wasn't firm? Like pad thicknes, brake lines' age, and finally fluid??

Not sure how/why you diagnosed a bad MC by "not firm" pedal...