1995 Ford Thunderbird Replaced rear pads, now the pedal goe

ALLSMILESJP

MEMBER
1995 FORD THUNDERBIRD
V8
2WD
AUTOMATIC
250,000 MILES

I replaced my rear pads and rotors due to normal wear. I bled all four calipers, using up a quart of regular dot 3 fluid and have a full fluid reservior. Whether the car is on or off, the first time I hit the pedal it goes to the floor with hardly any resistance. I have to pump the pedal to get it to brake, but then the pedal gets really hard to push. When the car is running and I'm holding the pedal, there is a hissing sound coming from the firewall. During a test drive I have to stand on the pedal to keep the car from rolling when it is stopped. Do you think it is air in the system or a jammed caliper piston. Or?

1 Reply

MATHIASO

MECHANIC
1,209 POSTS

The hissing sound is from a leaking power booster diaphragm, but that have nothing to do with the pedal sinking. Actually, you did not need to bleed brake after brake pad or rotor replacement.
You should bleed brake only if you have repair a leak, means anytime the system has been opened.
Here is what could be the problem:
look any extern leak, hidden place like below the booster. Leaking below booster means the secondary piston in the master cylinder is been bypassed.
Check all brakes line and connections for leaks.
If there no leak, and the fluid in the reservoir does not go down, then you have a bypass in the master cylinder at the primary piston cup caused by brake fluid contamination .
The master cylinder have to be removed and overhauled, and bench bled.
If contamination exist, the system should be flush with denatur alchool.