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Power brakes, front disc. All new brake system trying to bleed brakes. Can't get any fluid to come out of rear bleeders. My brake light in dash is on also, it goes out when i remove brown wire that attaches to it. So is the distribution valve stuck to one side ?? Brake pedal wont go down when opening rear bleeders. Any ideas how to fix, or reset this valve or is it something else. Could it be bad master cylinder ?? Thanks. Greg
Last edited by Zr1bandit; Oct 15, 2017 at 06:37 PM.
Although I have never had this problem, I think if you take the switch out you can take an awl or any thin pointy tool and move the little spool back to center. Then reinstall the switch. Then gently bleed the brakes so it does not shift over again.
Any idea which way to try and move the switch if im not getting any fluid to the rear breaks ?? Can i take out the switch part on the valve and try this while still on the car ??
You shouldn't have a distribution valve. You should have a proportionate valve.
Sorry, that is not correct. The 1967-1970 factory disk brake cars used the same distribution block as did the drum brake cars. The disk brake cars also had an in-line metering valve mounted under the master cylinder. Interestingly, they did NOT use a proportioning valve of any type. The metering valve is not a prop valve. The metering valve simply delays the application of pressure to the front disk brakes to give the drum rear brakes time to take up the slack in the actuating links. Combo valves have this metering function built in to the ports that feed the front brakes. A prop valve meters pressure to the REAR brakes to prevent premature lockup. The 67-70 cars used proper sizing of the wheel cylinders to get the right front/back brake balance.
So is the distribution valve stuck to one side ?? Brake pedal wont go down when opening rear bleeders.
This is EXACTLY the problem. The differential pressure switch piston is supposed to move all the way to the low pressure side to minimize fluid loss if there is a leak. Apparently you pressed too hard while bleeding the front brakes when there was still air in the back brakes. If crud is built up in the distribution block, the piston can stick. Try opening a front bleeder and press slowly on the pedal to try and move the piston back to center. If there is too much air in the back brakes, you may not be able to move it, however. Be careful not to go too far the other way. This is NOT a master cylinder problem.
This is EXACTLY the problem. The differential pressure switch piston is supposed to move all the way to the low pressure side to minimize fluid loss if there is a leak. Apparently you pressed too hard while bleeding the front brakes when there was still air in the back brakes. If crud is built up in the distribution block, the piston can stick. Try opening a front bleeder and press slowly on the pedal to try and move the piston back to center. If there is too much air in the back brakes, you may not be able to move it, however. Be careful not to go too far the other way. This is NOT a master cylinder problem.
So i gave in a bought a new replacement master cylinder to replace the original equipment one i rebuilt and now i was able to get fluid out of the rear bleeders and the pedal went down. The brake light is still on so i dont know what to think now. Never got the pedal to go down while bleeding the rear brakes with the old master cylinder. I am doing all this work with the car not running and these are power brakes. Gonna test brakes tomorrow but car not all together yet, will just put in gear and see if brakes will hold it still. Any other ideas on how to get the light out ?? Thanks. Greg
There are places that sell different variations of this to keep the shuttle valve from moving while you bleed the brakes. It goes in place of the brake differential pressure switch to lock in place.
There are places that sell different variations of this to keep the shuttle valve from moving while you bleed the brakes. It goes in place of the brake differential pressure switch to lock in place.
Nice tool, didn't know about that. May be too late for that now, How do i get them switch back to center ??
This is EXACTLY the problem. The differential pressure switch piston is supposed to move all the way to the low pressure side to minimize fluid loss if there is a leak. Apparently you pressed too hard while bleeding the front brakes when there was still air in the back brakes. If crud is built up in the distribution block, the piston can stick. Try opening a front bleeder and press slowly on the pedal to try and move the piston back to center. If there is too much air in the back brakes, you may not be able to move it, however. Be careful not to go too far the other way. This is NOT a master cylinder problem.
Sorry, that is not correct. The 1967-1970 factory disk brake cars used the same distribution block as did the drum brake cars. The disk brake cars also had an in-line metering valve mounted under the master cylinder. Interestingly, they did NOT use a proportioning valve of any type. The metering valve is not a prop valve. The metering valve simply delays the application of pressure to the front disk brakes to give the drum rear brakes time to take up the slack in the actuating links. Combo valves have this metering function built in to the ports that feed the front brakes. A prop valve meters pressure to the REAR brakes to prevent premature lockup. The 67-70 cars used proper sizing of the wheel cylinders to get the right front/back brake balance.
Joe, Is the '70 metering valve adjustable? There's a rubber button cover on the end that is under the master cylinder when mounted. Thx.
Last edited by Toms cutlass; Feb 4, 2018 at 06:54 AM.
Joe, Is the '70 metering valve adjustable? There's a rubber cover on the one end that is under the master cylinder when mounted. Thx.
No, it's not, and it doesn't need to be. Keep in mind that this is not a proportioning valve. It slightly delays application of pressure to the front disc brakes to give the rear drums time to "take up the slack" in the brake mechanism before applying the fronts. If the front brakes are applied too hard/too soon on wet surfaces, the back end can come around.
Thanks Joe, saved me time researching in the manual.
Q: I'm replacing the MC (power front disc/rear drum), and rebuilding/replating or replacing the brake booster. The metering valve is OE and still works as it should, but shows its age. For safety as well as appearance, would you recommend that I replace the metering valve as well, or just have the mounting bracket replated?
Thanks Joe, saved me time researching in the manual.
Q: I'm replacing the MC (power front disc/rear drum), and rebuilding/replating or replacing the brake booster. The metering valve is OE and still works as it should, but shows its age. For safety as well as appearance, would you recommend that I replace the metering valve as well, or just have the mounting bracket replated?
The metering valve is simply a spring-loaded piston with o-ring seals. Unless it's leaking, there is no real need to replace it. Of course, you can probably buy a repro with bracket for less than it costs to replate the original bracket.
