Brake Problem on my new to me 87

[zimmstoy]

Hey everyone,

Back againin the square body game. This time around I picked up an 87 GMC R2500 454 EFI Truck. She has been rode hard and put up wet. Still runs good. Trying to get a few minor things worked out.

The biggest thing bugging me on the truck is the brakes. When I start up and brake the first time they are almost too good (to the point that they lock up). After that intial brake, they get kind of soft on me. The first half of the pedal travel doesn't even slow the truck down. The second half of the pedal travel slows the truck down (not quick enough for me) and it never actually bottoms out.

My first thought was that this was something related to the booster being out. I had a hissing noise in the interior and had a problem like that in the past that the booster solved. Unfortunately this wasn't the case. After replacing the booster, the problem still exists. Previous owner says he did the brakes, master looks like its been there a while. There is also a fitting on the master that allows for an additional brake line that goes into the truck to a brake controller. I am planning on taking that out.

So my question is. Any ideas? Does this sound like the master failing, air in the lines or something else? Any advice / guidance is greatly appreciated.

Thanks!

[Buick455]

Sounds like the master cylinder failing as it sounds like your braking using only your back brakes. I am just in the middle of rebuilding my entire brake system on my 87 GMC V2500. I am installing everything new front to back, including lines. I am not sure if the proportion valve could be bad but that is also possible.

[zimmstoy]

Did the master and booster. Nada. Same situation. Went to bleed brakes and found rear drivers side wheel cylinder has some issues. Not sure its my entire problem but definitely part of it.

[zimmstoy]

Looks like the front brakes were part of the problem. Stops too well now.

The rears are locking up instantly when I go forward. What's next here? Were they over adjusted to compensate for the lack of front brakes?

[cableguy0]

If the rears are locking up instantly they are adjusted too tight. If you jack the rear up and try to spin the wheel there should be just a slight drag on the wheel. Anything tighter than that and they will lock up quick.

[zimmstoy]

ok - haven't gotten back there yet. do i have to remove the drums to adjust or should i be able to access from the backing plate? It's a 3/4 ton with the 14 bolt full floating rear.

[cableguy0]

so long as the adjusters arent frozen you should be able to pull the plugs on the bottom of the backing plates and loosen them up if need be. Jack the rear up and try to spin the wheels. If they are really tight back the adjusters off. If they arent tight you need to keep looking for your problem

[zimmstoy]

seems good now. drove it this am. 100x better.!!

[cableguy0]

Readjust the rears?