my master cylinder went on my vaccum brake conversion, so i bought a new one and within a week it leaked. the store i bought it from replaced it free, but heres what is worrying me now. when i had the first replacement on, the brake pedal felt a little hard, but not too bad. now, with the second replacement, the pedal goes down to the floor every time i use the brakes. the car stops, but the pedal goes all the way down. the MC is not leaking at all and is not losing any fluid. at work today, i bled the brakes again and when i first pumped the brakes up the pedal was hard again. after letting the car run for about 5 mins i got in to drive home and it wasgoing downto the floor again. what couldt his be? i dont know much about brakes, and i didnt see any other posts about this in the search
new master cylinder acting up....(vaccum brakes)
- Thread starter 87gninpa
- Start date
John Larkin
Sublime Master of Turbology
- Joined
- May 25, 2001
Try this: Adjust your e-brake pedal so that it is fully engaged after only 3 clicks while depressing the e-brake pedal. You tighten the nut on the e-brake cable adjuster just under the left rear floorpan. This gets the rear shoes oriented properly. Oddly, this helps sometimes. I think it's a 13mm nut; a few minutes with an open end wrench might help you get some pedal feel. If that doesn't work, try gravity bleeding all wheels at the same time for a few hours (clear hoses off all 4 bleeder valves dripping into small containers; just don't let the MC run dry).
Sounds like you still have some air in there
With a small amount of air, you will be able to pump the pedal up, but then it will be soft again next time you need it. Try this. Have someone step on (or pump up) the brake pedal and hold it for about 15~20 seconds. I don't really recommend pumping, as it can tend to aeriate the fluid if you have any appreciable amount of air in there, making it that much more of a task to get it all out. Patience is a virtue here. Then crack both lines at the master. The waiting allows time for any air that gets pushed down to rise back up to the fitting. If there is any air in that section, you should hear it spitting as it comes out. Repeat this till you get solid fluid. Once you have solid fluid there, adjust up the rear shoes first, then adjust the E-brake as John said, then bleed all four wheels, RR 1st, LR 2nd, RF 3rd, LF last. If the above steps don't get you a solid pedal, you probably have a defective M/C.
With a small amount of air, you will be able to pump the pedal up, but then it will be soft again next time you need it. Try this. Have someone step on (or pump up) the brake pedal and hold it for about 15~20 seconds. I don't really recommend pumping, as it can tend to aeriate the fluid if you have any appreciable amount of air in there, making it that much more of a task to get it all out. Patience is a virtue here. Then crack both lines at the master. The waiting allows time for any air that gets pushed down to rise back up to the fitting. If there is any air in that section, you should hear it spitting as it comes out. Repeat this till you get solid fluid. Once you have solid fluid there, adjust up the rear shoes first, then adjust the E-brake as John said, then bleed all four wheels, RR 1st, LR 2nd, RF 3rd, LF last. If the above steps don't get you a solid pedal, you probably have a defective M/C.
SINKING BRAKE PEDAL
HI! IT'S POWER BRAKE BOB. I WAS READING ABOUT YOUR MYSTERIOUS DROPPING PEDAL ON THE VACUUM BRAKE SET UP. THIS IS USUALLY CAUSED BY INSTALLING A DUST BOOT OVER THE END OF THE MASTER CYL. THE DUST BOOT IS ONLY USED ON MANUAL BRAKE MASTERS. IF YOU CRAM THE BOOT INTO THE VACUUM BOOSTER, IT PREVENTS THE VENTING NECESSARY BETWEEN THE BOOSTER AND MASTER. WHEN THE MASTER IS PUSHED IN, IT CREATES A VACUUM INSIDE THE MASTER, AND PULLS IN AIR INTO THE SYSTEM. THE STOCK REGAL MASTER WAS ONLY 15/16" AND DOESN'T HAVE STRONG SEALS. THE ONLY OTHER MYSTERIOUS PEDAL DROPPER IS LOOSE FRONT WHEEL BEARINGS. WHEN THE ROTORS WOBBLE AROUND, THEY KNOCK IN THE CALIPER PISTONS, AND YOU HAVE TO PUMP THE PEDAL TO PUSH THE PISTONS BACK OUT. WE ARE SELLING THE NEW BOSCH (BENDIX) HYDROBOOST SYSTEMS TO PROVIDE A SUPERIOR BRAKE ALTERNATIVE TO THE VACUUM BOOSTER OE THE POWERMASTER. THE UNITS USE A 1. 125" MASTER, AND THE HYDROBOOST RUNS OFF THE POWER STEERING PUMP, THUS REQUIRING NO VACUUM. THESE HYDROBOOSTS CAN RUN FOR 200,000 MILES WITH NO SERVICE NEEDS EXCEPT CLEAN OIL YOU CAN SEE THE HYDROBOOST AT POWERBRAKESERVICE.NET BOB
HI! IT'S POWER BRAKE BOB. I WAS READING ABOUT YOUR MYSTERIOUS DROPPING PEDAL ON THE VACUUM BRAKE SET UP. THIS IS USUALLY CAUSED BY INSTALLING A DUST BOOT OVER THE END OF THE MASTER CYL. THE DUST BOOT IS ONLY USED ON MANUAL BRAKE MASTERS. IF YOU CRAM THE BOOT INTO THE VACUUM BOOSTER, IT PREVENTS THE VENTING NECESSARY BETWEEN THE BOOSTER AND MASTER. WHEN THE MASTER IS PUSHED IN, IT CREATES A VACUUM INSIDE THE MASTER, AND PULLS IN AIR INTO THE SYSTEM. THE STOCK REGAL MASTER WAS ONLY 15/16" AND DOESN'T HAVE STRONG SEALS. THE ONLY OTHER MYSTERIOUS PEDAL DROPPER IS LOOSE FRONT WHEEL BEARINGS. WHEN THE ROTORS WOBBLE AROUND, THEY KNOCK IN THE CALIPER PISTONS, AND YOU HAVE TO PUMP THE PEDAL TO PUSH THE PISTONS BACK OUT. WE ARE SELLING THE NEW BOSCH (BENDIX) HYDROBOOST SYSTEMS TO PROVIDE A SUPERIOR BRAKE ALTERNATIVE TO THE VACUUM BOOSTER OE THE POWERMASTER. THE UNITS USE A 1. 125" MASTER, AND THE HYDROBOOST RUNS OFF THE POWER STEERING PUMP, THUS REQUIRING NO VACUUM. THESE HYDROBOOSTS CAN RUN FOR 200,000 MILES WITH NO SERVICE NEEDS EXCEPT CLEAN OIL YOU CAN SEE THE HYDROBOOST AT POWERBRAKESERVICE.NET BOB
