I have a 92 4x4 with brake issues. Since I got it a couple weeks ago the brake pedal will go most of the way to the floor before the brakes engage, and when they do they don't have much pressure. It's still safely driveable with caution, but won't pass inspection. When I bought it there was a box in the back for a master cylinder so I assume it was replaced, though with the condition of the vehicle I wouldn't trust how well it was done. I tried bleeding the brakes, which got a lot of air out of the back and very minimal out of the front. After that the brakes felt fine, up until about the third stop when the pedal pressure went back to what it was before. I looked around some more and found my back drivers drum drenched in brake fluid, which it wasn't before. Replaced the bad wheel cylinder, as well as most of the springs in that side, bled the brakes again and it was fine for about five minutes of driving before the pedal floored as I came to a stop. Back where it was before. This afternoon I went out and pumped the brakes for a few minutes with the car off; no pressure built up and no fluid leaked out from anywhere, and I got the same results with the car turned on. I also checked the fluid level during my test this afternoon, which showed no change. So i've come to the conclusion that I'm sucking air in from somewhere, but I haven't worked much on brake systems and am dumbfounded on what to do next. Any advice at all?

 

Sounds like a bad master cylinder. One pretty sure clew is if you ever feel the petal fading, sinking down like it's cup isn't sealing.

Also the auto adjusters in the rear's rarely work right, and the adjustment of that star wheel is directly related to the petal free play. Course other things can affect the petal, but that needs to be right.

 

UPDATE: per a suggestion to me I hooked up a brake bleeder pump to the bleeder nipples. I started with the back passenger and it pulled massive amounts of air. My first thought was that the connector on the end of the hose was allowing air around it, so I closed the bleeder nipple and got a vacuum going with a bit of fluid in the end of the hose. At about 20 psi it started to slowly allow bubbles around the connector, so I know the massive amounts before were actually from my brake line. I'm kind of surprised it stops at all... Anyways, I had the same amount of air come out of all four brakes, suggesting a hole somewhere upstream of where they split off. but looking at it, I have my master cylinder and that runs down to the brake proportioning valve directly below it. So I'm gonna go hook up my bleeder pump under the p/valve and if I'm still pulling air I'll try it directly from the master cylinder.