Mrspencer

HELLO ALL, MANY MANY THANKS TO ALL, for helping me sort out my latest midlife crisis,lol,anyway,on my way into work my brakes pedal becomes soft so I bleed the system at work, no visible leaks anywhere pedal felt good , so home I go turn onto my block and no pedal 4 pumps later cars stops, parking car in driveway pull wheels no leaks, so here is the issue either during the R/R of the master I hear a hissing sound like a like the booster releasing it's vacuum,so put everything back together, during the bleeding at the master I hear a fsssh fsssh sound everything we push on the brake pedal, after the bleeding the pedal is, to firm as if the is little booster assistance, has made my check valve at the booster failed, also no fluid in the booster, thanks in advance. 85 s3 5spd.

Mrmerlin

In a perfect world I would suggest this,
buy a new booster and master cylinder and a liter of ATE fluid and a new check valve,swap in new stainless flex lines, get a tube of DC111 for the reservoir grommets and the MC base seal O ring

Bleeding damaged the MC seals, its done.
The rubber seal at the back of the MC could have been damaged or lost or the sealing surface for the booster has been damaged.

No telling if your booster is still good so replace it while the MC is out of the way.

all told the parts will never be cheaper than today,
and you will have great brakes when your done

928NOOBIE

My booster went out and did exact same thing...making hissing noises and maybe get 1 or 2 good pumps of the brakes then goes firm. I was stupid enough to drive the car until the booster fully failed...for those curious folks what happens is the brake pedal goes BONK! with downward maybe 1/2 inch and immediately you feel like someone put a brick under the brake pedal....if you are like I was and roaring up to a stoplight you get to go home and change your pants because you almost rear ended the car in front of you...no more power brakes for you!...so yeah change out that booster bud ..

Mrspencer

Many Thanks sourcing one now.

Mrmerlin

what part are you planning on replacing?

based on your last post only one

Mrspencer

Check valve,and grommet, re-check pedal if still hard then BOOSTER,MASTER IS ALREADY NEW.