I have a 69 nova that the rear brakes as you use them the pressure builds and they start smoking,I have pulled the master line off and it still keeps pressure on back brakes, I then replaced the proportioning valve and that didnt help at all. What would still hold the pressure on the back brakes?:confused: Thanks for any help

It is possible the flex line from the frame to the differential is bad inside. It has an iner and outer layer so it can not be checked visually. Unhook at the upper connection first. If the problem is the hose the pressure will still be on the wheel cylinders.

Are you sure it is line pressure and not a defective star self adjuster set on self destruct? If it is broken it will ratchet itself into binding the rear brakes which will have no effect on the hydraulic lines.

There is a check valve in the line that keeps partial pressure on the disc brakes so the pads do not drag and make a noise. Are you sure the lines are feeding the right system (front or rear). The check valve inadvertently set on the rear system will result in this condition also.

Big Dave

I was thinking along the same lines as Big Dave with it being something in the mechanical part of the brake system.

The lines are new, I dont think it would be the star adjuster on both sides, When the brakes hold on I loosen the bleeder and get pressure out of it and they release. How can you tell if the check valve is set on the rear brakes?

John never rule out a part because it is new. Did you replace all the lines and master cylinder at the same time? If not what was the last item changed prior to the problem occuring?

The master and all lines were replaced front to rear at the same time The only thing that was added that was not on it before was that check valve, could that check valve hold pressure in the line ?

Yes that is what they do. Where in the system is it located? You shouldn't need a check valve on rear brakes. The return springs need to push the fluid out of the wheel cylinder to release the brake shoes from the drum. As long as the adjusters are working the shoes will maintain the proper clearance from the drums.

The valve is on the driver side frame where they had it from the factory.

This is a factory disc brake car? If so the valve should be a delay valve and the other is just a separator block to isolate front and rear systems. It is the exact same one used on drum/drum systems. The delay valve was the proportioning part of the system. The all in one valve didn't go into production cars until 71. If you are using a newer proportioning valve with the factory delay valve that could be the problem. Can you post photos of those two items?

Here is a photo of the valves I removed from a 70 Impala. The lines will be different but the components will look the same. Are these the parts you have in yours?

If you have an all in one proportioning valve it will have a rubber covered button on one end like the delay valve in this photo. I do not think the 2 valves will work together.

http://i80.photobucket.com/albums/j199/64elcamino/delayvalvesm.jpg

no i dont have a valve with a rubber covered button.I have a 69 camaro with front disc like the nova and they both have the same set up. I still think it is that check valve on the frame I am going to a show sunday to see if I can pick one up. That is the only thing that is left on the line.

You can check it by opening the line on the rear side of the valve to see if the pressure bleeds off, if it does the valve is the culprit.

That is my next move, I will do that soon Thanks John

69yenko i had that happen to me once and it burnt the clutches up in the trans ,anyways what it was ,was the brake rod was to long and keep pressure on the back brakes.i had to open the lines on the master cylinder to relieve the pressure to get my sons car home.i shimmed the master cylinder and took care of the problem.

067 I opened the lines on the master cyl and it still had pressure out of the rear bleeder.

if thats the case then it has to be the rubber line or the self adjusters are keeping the brakes to tight as some of the others have said allready.

It was a bad check valve. Thanks for all your help. John