Sticky Brakes
I have a 1995 K2500 HD truck with an automatic transmission and a stock 350ci engine. My uncle bought the truck new. Within a year the rear drum brakes started to lock up. The dealership replaced the drums, and it seemed to help for a while. He replaced them two other times. When I got the truck I replaced the drums and breaks shoes. That worked for a few weeks then it started locking up again. I replaced the drum shoes, all the springs, and the wheel cylinders I still have the same problem. Any ideas what could be going on?
William
Via nuts@4wheeloffroad.com
Since all of the hardware out back is new and presumably installed correctly (maybe double-check that), I would suspect a problem with either the master cylinder or the brake proportioning valve. The brake drums themselves don't normally cause problems with the brakes prematurely locking up, and since it sounds like this has been an ongoing problem since the truck was new, I suspect the problem is somewhere other than the rear brake assemblies. The proportioning valve's job is to regulate the amount of brake pressure going to the front and rear brakes, but on drum brake systems it also holds some pressure in the rear brake circuit. If the proportioning valve has become contaminated by trash in the brake circuit or is simply malfunctioning, it can be holding excessive pressure to the rear brakes, causing them to drag and prematurely lock up. This drag will cause the drums and shoes to wear out prematurely. The same condition can be caused by a sticky master cylinder, though usually master cylinder problems are accompanied by a spongy brake pedal and poor braking performance.
Pop the cap on the master cylinder and have a look at the brake fluid. If it's dark or has any particles in it, flush the entire system thoroughly. While you're at it, inspect the metal line going to the rear brakes and make sure it isn't pinched. If the fluid is heavily contaminated and the truck has been sitting for a long time, the brake lines can start rotting from the inside out and get clogged with rust, so the lines may need to be taken apart and blown clean or even replaced. Should you find clogged lines, then you might as well replace the rubber brake hoses while you’re at it. If everything checks out and the problem persists, take a closer look at the proportioning valve. Sometimes it can be taken apart and cleaned, but again, since this truck has had this problem since nearly new, I'd recommend replacing it.
