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Originally Posted by impulsive78
I have a 77 K5 Blazer and the rear brakes don't work. I've been having some brake trouble(replaced the booster,master cylinder, and regulating valve). When i try to bleed the rear, i get no pressure, when i bleed from the rear resivoir of the master cylinder i get pressure. When i undid the line that goes to the regulating valve from the rear of the master cylinder i get pressure. When i undid the line coming from the regulator valve to the rear brakes, i get no pressure. Is it possible that this second rebuilt regulator valve is bad? My front brakes work great but the back don't, and now i'm starting to wonder if the rear ever worked at all. Any ideas?
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I have the same problem with my '77 GMC Sierra. Whats happing is that the proportioning vave is becoming un balanced. You need to re center the valve by connecting a test light to the brake light wire and then to a 12v sceorce. The test light should be on. Then you have to open the front caliper bleed screw and pump the brakes untill the light goes out. Once the light is out, your valve is now centered.
Bleed the system as normal. If it happens again, you have to re center the valve again. It can be a real pain in the ass. I'm going through the same issue with my truck. You just have to get all of the air out of the valve and rear brake system for it not to go over center again.
Hope this helps.
