Chevrolet Repair: Rear brake problem, flex hoses, rear drums

Question
Hello Van, I have a 1988 C3500 2 wheel drive with rear anti-lock,5.7. Intermittently the rear brakes will hang up. You put it in drive or reverse and you can barely move.Than it will free itself and be fine for weeks or maybe act up in a couple of days.The brake light had been coming on so I replaced the computer.No change.Is the brake light coming on giving me a code.It seems such a simple system but is giving me a real problem.I have a new combo valve but am thinking that won't probably help.Is there something else which could cause pressure to the rear drums? The front does not lock-up or drag.I have a feeling it is all connected to the rear anti-lock.Any direction or ideas would be appreciated. Thanks  Doug

Answer
Hi Doug,
The parking brake system could be hanging, but I doubt that.
There is nothing to send pressure to the wheels except the master cylinder. It is possible the master cyl is not totally releasing.
I have also seen flex hoses deteriorate internally, and the rubber plug the line, acting like a check valve, and hold the brakes applied. But the only place I saw that was in the front flex hoses. But there is no reason the rear one couldn't do the same thing.
When they lock up next time, open a bleeder screw on one of the rear wheel cylinders, and see if pressure is trapped. You can also crack the line to the rear wheel portion of the master cylinder, and see if pressure is trapped there. Of course, this may take a couple different occurrences, but that way you can narrow it down.

Good luck,
Van