10-01-2007, 07:14 PM
My 94 was making some rear break noises so I got some new shoes for them. It so happened that when removing the drums that I noticed a lot of dirt and rust but the shoes definatly did not not to be replaced at 135k. So my friendly mechanic just cleaned the break parts: While doing this we noticed that if I put my foot on the break the pads did not move. Also if I loosened the nipple the line would not bleed. Whats up here? Can someone explain what is suppose to happen to the rear breaks when the pedal is applied?
10-26-2007, 01:37 AM
This has to do with the load proportioning valve. Once the wheels are on the ground you will be able to bleed the brakes. and also see the shoes move, but i would not do this with the drum off
09-25-2008, 07:14 PM
I had a problem with my rear brakes on my 94 extended cab p/u. I went to stop and I almost rear ended a caddy. I replaced the brake master cylinder/ brake booster and all the soft brake lines and bled them with a vacuum bleeder. still did not fix so I brought it to a mechanic who replaced the front brakes and then found out that the rear proportion valve had an anti skid? design. it had an arm that attached to the frame and went to a piston in the valve. if the truck would start to lean to the side (like when the rear brakes would lock up and the rear end would swing around) it would push the piston in and relieve the pressure to the rear brakes which would let them release. what he found was the old valve had corroded and froze with the piston shutting off the rear brake line. he replace it and now good as new. he also said that the rear brake pads looked brand new and were still good. in the 32 years he had worked as a mechanic that was the 2nd one he has had to replace. hope it helps.
09-30-2008, 11:03 PM
The proportional valve is a Load Sensing Proportional Valve (LSPV). It's dependent on the amount of weight you put in the bed or needs to be readjusted if you put on a lift. As the bed gits closer the the axle, the connecting rod closes the distance in the valve. As you press on the brake, the valve rod extends out to contact the connecting rod and this will increase the amount of brake fluid (pressure) to the rear brakes. The anti-skid portion should be in the engine bay if you have this feature. Follow yer brake lines from the master cylinder and you should find the anti-skid device if you have it. My 1993 T-100 has one that has the power steering fluid going through it.
I had to smack the crap out of mine on the outside with a 2x4 to break any crap inside of it free. Mine was not allowing enough pressure/fluid through it as well. I jacked up my differential and could spin my tires and jam on the brakes. The tires would still keep rolling! :(
I've been looking fer a spare one to tear apart so I can show people what it's made of and what servicing you can do to them. ;) Anyone got one lying around that they don't want? :D