I have a 70 GS with a factory front disc set-up. Over the years I have had some things on the car chromed, including the power booster, master cylinder, metering valve and other engine parts. I have had all this chrome stuff on the car now for about 3 years and the brakes have been ok. However just this winter I needed to remove the power booster and master cylinder to do some other stuff and when I went to bleed the brakes I have basically 0 pressure to the rear wheels. The fronts seem fine and I noticed the Master cylinder leaking a tiny bit so I rebuilt it thinking that might solve the problem but it only stopped the leak. Anybody out there have any thoughts? Can a proportioning valve just go bad all the sudden? Some people have told me "many guys just pitch them metering valves cuz they never worked from the beginning" Doesn't the metering valve just reduce pressure to the front wheels? Any help would be appreciated, Rob
I have two thoughts, both from problems I have had on cars. 1 Rubber line on the rear from frame to rearend. I have had those collapse inside. 2 A little brass residual valve thingy. It is just a little thing located in the line going to the rear, if you follow the line back, after the proportioning valve you will find it, if yours even has one. Mine was on a 69 Firebird Convertible I had. It was brass and located in the line about under the rear of the door. Mine was bad, I took it off and threw it away, the lines were flared of course so I put a brass flare fitting union in its place. Anyway, both these can be checked by cracking the line going in,,,and out,,,both ends of the line. As you will have fluid in front of the problem but not at the back of the problem. Simple way to isolate the problem, but not always easy.
Re-bleed the master, only the rear reservoir. No need to take it off. Either make a line the bends up into the reservoir or spend a few bucks to get the variety pack of "HELP" fittings with clear rubber hose and do the same. You need to verify that you have gotten all the air out. How did you bleed the master before? Was it level when you bled it? If so its very possible air is still trapped inside. You will need to tilt the master assembly while you bleed it. Next, like phelps said above check the rear "splitter" line. Once you have confirmed you can get fluid past the master have someone step on the brake while you crack the hard line before the splitter and verify fluid is going to it. If it won't go through its collapsed. If you have trouble locating a replacement, try a C/K Chevrolet GMC 1500 from the 80's. I did and it was virtually the same, no modifications needed. Granted it was my Electra but bring your old one in to match it up. I doubt its the proportioning valve. I've had alot of people tell me that is the problem, its very rare. People are quick to blame the proportioning valve and tell you, its not needed. Hope this helps.
And while under car looking up, working on brakes, be extremely careful not to get brake fluid in your eyes. Hurts really bad and probably really bad for the eyes. This is the voice of experience speaking.
Thanks for the input guys. I will try rebleeding the master again and look for the brass do-hickey, while I keep my eyes safe:TU: I will let you know if I have any success.
He's right. I once got brake fluid in the eyes when I was in my 20's. When I turned 50, I needed reading glasses.
That's too funny. I think I have enough pressure now. I still have the car up on jack stands and some more stuff to do underneath before I test drive it, but the pedal is wayyyy better. I removed the rubber line from the rear end and then disconnected it from the proportion valve. I then blew air through it. then I disconnected the line from the master cylinder and blew air through it. Then I reconnected the rear hose and opened the bleeder screws and blew air through that. With no restrictions at all I hooked it all back up and rebled the master cylinder again (for about the 3rd time) Then bled the whole system again. Now it seems good. Don't know for sure what I did that solved the problem but I'm crossing my fingers till I get it on the ground.
Sounds like you have the problem taken care of :TU: Just from my experience I've also had the rubber hoses collapse on the inside, but in every cases when it happened it allowed fluid to pass through just fine under pressure, it just wouldn't release the pressure.
