97 ford brakes

I have a 97 taurus that sat with the transmission out of it for 5 months. When I put it back together the left caliper seemed stuck, so I replaced both
calipers, rotors and pads. I started driving the car and after several times of braking , I heard what seemed to be a vavuum leak and then the brakes started tightening. I investigated and found no line blockage but all 4 wheels were tight and wouldn't turn. I replaced the master cylinder and bled everything, problem still exists. I have to bleed off the master cylinder to get them to release. I pulled the master cylinder back away from the booster and it seems the booster pushrod is staying extended and not always retracting until I bleed the master cylindern then its good for about 8 or 10 times of braking. this is when the hiss or vacuum leak appears and starts locking up. I can see the booster diaphram leaking, but why doesn't it allow the rod to retract. Would this be a booster problem or something else like the proportioning valve?
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I would simply replace the booster... since you can hear a hissing (from inside the car, right?? from under the dash, right??) i would hazard a SWAG that the booster atmospheric valve is leaking and applying the brakes for you (or in spite of you)...
If the booster diaphragm were leaking, you would notice increased pedal effort.

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Thanks for all the help. I pulled back the master cylinder when the brakes were tight again, just too ease my concious before buying a new one. Guess what I found that I didn't see when I origionally repalced the MC, the adjustment rod for lengthing the brake pedal had come loose and was extended all the way out. I don't know if this happened when the MC started leaking or what but I ran it all the way back in and the problem no longer exists. Who would of thought the rod would back itself out and cause this kind of problem. ? Thanks again guys. Ron S
Jim Warman wrote:

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Ron Schoeneweis wrote:

Hmm, interesting. When you pull the MC back from the booster, do the brakes release? Your post doesn't quite indicate that. If they do, I would suspect the booster. If they don't fully release with the MC away from the booster, I would suspect the MC. 5 months isn;t really a long time, but you never know what down time will do to an automobile.
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