Need your thoughts-Rear brakes won't release

Been putting discs on the 55 Chevy, used a CPP M/C and a Speedway prop. valve. The rear brake cylinders were toast, so I replaced them too. Now the rear brakes will not release unless I open the bleeder valve. What do think is the problem? I have bled the M/C and entire system several times, and can't figure this out unless the M/C or the prop. vale is faulty. Thanks.

 

Somethings holding pressure still. Check to make sure the pushrod is adjusted properly.

 

My 32 has power brakes and is doing the same thing. If I disconnect the vacum line it stops hanging up. Not a biggie on such a light car. I sure would like it to stop though. Kills the battery because the brake lights stay on if I don't catch it.

 

Check the pushrod and the rear flex hose - might be an internal blockage.

 

This is not a power brake system.

 

rear flex hose has collasped inside = replace it and also replace the front ones if they haven't been replaced.

 

The rear brakes seem 'reluctant' to move. It is almost like there are two stages of brake acuation. They won't move until a lot of pressure is applied. The rear flex hose has not been relpaced, but the fronts were.

 

This is what my problem was when I did the brakes on my 55. Youd be surprised.

 

when the flex hose collapses, the inner hose has a rip in it,so when you put on the brakes,brake fluid pushes the flap of brake hose up, out of the way. This allows the fluid to travel down the flex hose,causing the brakes to apply, but as soon as you release the brake pedal, the flap of brake hose falls down, blocking the return flow for the rest of the brake fluid ( under pressure)from the wheel cylinder to the master cylinder. This causes the brakes to lock up.
Replace the flex hose, your brakes will be fine then.
Roger

 

thanks guys. A new hose it is. The rod adjustment didn't change anything. This car has fought me all the way on this brake deal.

 

I have had this problem a couple of times, some times the after market proportioning valve has too much resistance for your master cylinder. This may not be your problem, but it only takes about 10 minutes to try....Take the rear fitting out of the proportioning valve. You will find a small spring and a cone shaped piece of rubber. Take them out, re-assemble. See if it works then.

 

One thing to note, this is if you used the non-adjustable brake proportioning valve same as GM valve used on many cars in the 70's. For disc front/drum rear Speedway part #910-31364.

 

Do you have a residual valve in the rear brake line or built into the master? I'm assuming you used a disc/disc master? Disc/Drum master with built-in residual would hold too much pressure for the disc setup.

Also, make sure the prop valve isn't installed backward.

You can crack the line at the master and see if the brakes release. If not, keep cracking the line at each fitting toward the caliper until the brakes release. That will at least tell you where the pressure is being held.

 

Prop valve, (no residuals) is in the rear brake line. It is a Speedway adjustable type. Thanks for the tip, exwestracer. I will do that.