I have a 1985 Subaru Brat 3-speed automatic. My brakes were trash and squealed really bad so I replaced the pads and rotors and had to replace the calipers too because the Piston wouldn't go back in. Got those installed and went to bleed the brakes and the pedal goes straight to the floor. It doesn't build any pressure at all. I attempted to bleed the brakes anyway but like I said it doesn't build pressure and if you pump in a bunch of times in a hole to the floor and open the bleeder valve brake fluid just dribbles out. Figured I somehow messed up the brake master cylinder so I got a new one and installed it and no change at all. I bled the master cylinder and the calipers multiple times as well and it still just dribbles out. I know brake booster uses vacuum, so I think it has something to do with that because, when I hit the brake pedal air gets sucked into the carburetor. Also when the vehicle is running if I hit the brake it stutters and almost dies. I don't see any drips or anything from the brake lines, calipers, or MC. 

Any ideas what could be wrong? Do I need a new brake booster? I'm honestly kind of stumped.

Sounds like your booster has a ruptured diaphragm.

Rock Auto doesn't have a new brake booster in stock. I do have an 89 GL 5spd D/R parts car. Will the brake booster from that work? They're showing up as different part numbers but if I just have to make a longer vacuum line or bend the brake lines a little bit it doesn't bother me.

It's not the booster. Even if the spring inside the booster were to break, It wouldn't cause the pedal to go to the floor. Did you bench bleed the master before installing it? If not, that could be your issue. You need two people to bleed the system properly, or a vacuum bleeder or a one man bleeder hose with a check valve. Bleed in this order: RR, LR, RF, LF after you bleed the master.

Keep going with each corner until you get clear fluid and no bubbles.

not to be against Skishop69,

but my pedal would go straight to the floor with little pressure on my EA71, i swapped it with an EA82 Master cylinder because of the lack of parts, and after modifying it heavily it still went straight to the floor, swapped the brake booster and now it feels like any vehicle, not sure why it was the brake booster, made no sense... just saying.

but it could be air in the lines too, before going to extremes, like Skishop 69 mentioned, try properly bleeding, and even doing it with 2 people isn't the "proper way" of bleeding, buy a $6 vacuum pump.

Edited August 9, 20187 yr by Subasaurus

I'm pretty sure my parts car GL still has the brake booster so I can try to swap the booster and the master cylinder and see if that works. If not I'll go from there.

well theres not much more to go through once you swap those out and bleed the lines completely, unless you see fluid dripping on the floor everytime you brake.