Problem with rear brakes overheating

[spamtank]

I have a 70 Challenger SE, 383 2V, AT, front disk brakes and rear drum (10").  About 3 weeks ago, I had her on a 20 mile trip, mostly stop and go traffic with a max speed of ~40 MPH.  about 30-40 minute into the trip the brake warning light came on.  When I touched the peddle the light went out.  I initially thought I had a fluid leak.  I pulled on to a side street, and decided to set a course for home.  Turned out the rear brakes were over heating. 

Once I got home took everything apart and replaced wheel cylinder and installed a new spring kit of the course of 2 weeks.  I made sure everything was clean and put a light film of never seize on all sliding surfaces.  Everything seemed to be free and working fine.  I bled the system and adjusted the brakes for a light drag and then backed off 3 clicks.

Ran it around the neighborhood and they seemed fine.  Today, I took it for a quick highway ride, and the right rear brake started overheating first.    Then the left rear did too.  Before too long they were just about locked up.

When the brakes cool down the drums slide right off (probably eroded away much of the shoe).

Since this was a 2 bbl car, it came with single exhaust, but had dual exhaust added later.  Is it possible there is a brake line heat shield that is missing near the muffler?  I sort of wonder if the fluid to the right rear is heating, causing it to expand and exert braking force, which then causes more heat, and it snowballs from there.

Any suggestions?  I'm at the end of my rope.     I've worked on drum brakes off an on for 35 years now.  Never ran across this problem. 

[Road_Runner]

That sounds similar to a problem I had with mine not that long ago.  The emergency / parking brake pedal was hanging just a little shy of being completely disengaged and was causing the rears to drag.  The pedal looked like it was all the way out but apparently wasn't.  I pressed & released the pedal a few times and it hasn't happened again, but I know I need to fix the parking brake because it doesn't lock enough when all the way in either. 

Later, Jim

[72rtchallenger]

yea I agree  the parking brake would be the first place to start

[Moparal]

Check the rubber brake hose at the rearend Tee. It may be colasped and not letting the fluid release.  Another thing to consider

Even the wrong master cylinder installed can hood pressure.  In 70 as I recall, there is a difference in 70 pwr disc, 70 standard disc, 70 standard drum and 70 pwr drum.  The master cylinders will look the same but with or without a check valve of some sort.  Something is holding pressure that is obvious. Seems if your e brake was tight, the drums wouldnt slide right off. A colasped hose will bleed off eventually

[jimynick]

I'd look at if you've got the leading/trailing shoes in their right spots, distribution valve grief or perhaps a brake line/component near a heat source. If the drum goes on and off cleanly, it's not likely the parking brake unless you've applied it during the drive. 

[Bullitt-]

Yea check the rear brake hose, I was told that you can have an internal rupture that will balloon and hold pressure on the brakes but show no outer signs of leaking.

[spamtank]

That sounds similar to a problem I had with mine not that long ago.  The emergency / parking brake pedal was hanging just a little shy of being completely disengaged and was causing the rears to drag.  The pedal looked like it was all the way out but apparently wasn't.  I pressed & released the pedal a few times and it hasn't happened again, but I know I need to fix the parking brake because it doesn't lock enough when all the way in either. 

Later, Jim

Thanks Jim.  This weekend, I'm going to try to determine if the cable is binding.  In any case, I'm going to replace the E-Brake cable and associated components.   Might be looking for some of this stuff at Carlisle.  I know Classic Industries has a complete kit. 

[spamtank]

Check the rubber brake hose at the rearend Tee. It may be colasped and not letting the fluid release.  Another thing to consider

Even the wrong master cylinder installed can hood pressure.  In 70 as I recall, there is a difference in 70 pwr disc, 70 standard disc, 70 standard drum and 70 pwr drum.  The master cylinders will look the same but with or without a check valve of some sort.  Something is holding pressure that is obvious. Seems if your e brake was tight, the drums wouldnt slide right off. A colasped hose will bleed off eventually

Hey Moparal, thanks.  I'll check that.  The brake lines seem okay from the outside.  I think I'm going to attack the ebrake cable since both times I had the issue I recall "trying the e-brake".  But, next on my list will be to replace the old steel lines and hoses.

Again thanks!