I replaced the Master Cylinder on my girls 96 sl after bench bleeding to were I could no longer stroke it any more then the 1/8" as per institutions put it in and bled the breaks using a vacuum bleeder using over a quart and a half of fluid from two new bottles topping off the Master after every two OZ of being pulled through the system ' I know over kill ' but this is my babygirl's life after all When I was done took the thing for a test-drive all was great the peddle only went down about 1/2-3/4's of an inch until it wouldn't go anymore the breaks were Perfect!! she went to work yesterday afternoon no trouble at all.. She got off at one (1) AM went to leave and the peddle went to the FLOOR I went and checked the hoses lines wheel cylinder's every thing was dry no leeks anywhere the master is still full of fluid to the line where I marked it with a marker Can anyone give me any ideas as to what can be the cause of this? I jacked the thing up used part of the handle to hold the peddle down and tried with a 36" breaker bar to turn the wheels and could not budge them!!!

 

Question(1) --> Did the pedal go to the floor repeatedly, or was it just one time? Reason I ask, you later state that when you checked the brakes, they seemed to respond properly.

Question(2) --> Did you purchase the master cylinder through GM or did you get a "rebuilt" from the local parts house?

I'm suprised at the tiny amount of pedal travel you mentioned. Most drivers would be standing the car on it's nose.

 

The peddle will go to the floor by just using finger tip pressure on it and will not pump up at all it's like the master is not even there I just pulled it off the booster and it will not let me push it in anymore than an 1/8" by hand I thought it may been binding on the booster but when I pulled the nuts from it. It stayed rite there against the booster.

It's new from GM it had one from Autozone that did the same thing and another from another one from Dorman. and their all doing the same thing.. Anyone have a stick of TNT? lol

 

Go on the internet and search trouble shooting brakes. We could sit here all day coming up with posibilities ........ when all you need to do is go read and learn.

 

NTB did the first master from autozone she was out of state with the car when the next one was put in at Goodyear auto service. And I did the one From GM myself and if you WILL READ IF I take it OFF THE BOOSTER AND TRY THE PISTON I ACN NOT GET IT TO MOVE THEN AN 1/8" of travel and I even used the tool to test the push-rod to MASTER to check for the proper rod length to make sure the pushrod was not to long and it's within 0.10 thousands witch is more then the acceptable range!!! And like I stated before IF I TAKE THE MASTER OFF I CAN ONLY GET IT TO MOVE AN 1/8" OF AN INCH!!!

W Greathouse
ASC MASTER TECH with over 30 Years turning Wrenches