My brakes have always felt fine, normal pedal pressure and everything. I replaced my transmission two days ago and after i finished the job i test drove the car and the brakes functioned normally. The next time i drove it that day the pedal will go to the floor on the first try and then once i pump it once or twice they have pressure, though quite as strong as normal. I checked the brake lines at each wheel where they connect to the hardlines and where they connect to the calipers, no leaks. Same with the master cylinder, no visible leaks whatsoever. I just checked the fluid level in the master cylinder, cause i filled it yesterday, and there is no fluid loss.

Any ideas on what this could be? I'm thinking possibly a bad master cylinder that is bypassing internally? but do they go out that quickly?

Any help is very appreciated

 

did you let any air into the system?

so you just filled your master cylinder yesterday for what reason? (i'm just trying to understand better)

 

im having the same issue on my 91 randomly the pedal will go to the floor and then pump it and it will b fine for e for days sometimes it happens a couple days in a row but i havent changed anything

 

its bypassing internally, i had this issue on mine, no visible leaks after rebuilding the rear brakes, blew the front seals on the calipers out and then i was still loosing pressure, tried my friends eg one and same thing (turns out his is doing the same exact thing)

 

JUST BLEED your system out for any air ?
just to be on the safe side a car with no brake?= fail

 

No air was introduced to the system, like i said the brakes worked fine right before my transmission went out, the car sat for a week, and now this. I filled the master cylinder just so i would have a good reference as to where the fluid level was so i could tell if it was loosing fluid. I'm going to go get a master cylinder tomorrow. I need to change my proportioning valve anyways to the 4040 i have for my rear discs so it gives me a good excuse to get it all done haha.

 

it does sound like a master cylinder going out. its just one of those things that just go out on 20 year old car.

 

+1 for master cylinder.

likely a leaky seal or whatever. just replace it... like $50 from autozone.

 

i had the same exact issue recently, i bought a bran new MC for my ed and intalled it and bought a bleeder pump, turned out there was alot of air bubles in my system, and on top of that the previous owner never did maintanace on the breaks so while bleeding them it was black and on one side it was even coming out like syrup, not i have clear new liquid going through all 4 corners and it brakes way better than before