I have a 1972 chevelle ss with drum brakes in rear disk up front. all the master cylinder and rear brakes have been replaced and work for a wile then stop quick and get home to burning breakes drum hot as heck, what causes that?

have you change brake hoses maybe bad inside.

no they bleed great when pushing brake peddle

Check your E brake adjustment.

If you have the slightest drag with drums they will heat up and lock.

I will try to losen the drag up a bit and see if that works. can they catch fire if they get to hot when driving home from car show

I guess it is possible if the tire gets hot enough, but doubtful.

Make sure the cable has slack and then adjust the brake shoes so that you hear just little to no drag when turning the tire.

As long as your pedal height is good you should be good to go.

Thanks for you reply and help will check this out see how it works going to car show this weekend

sounds like what gary said bad rubber hose over rear if it releases after sitting a while

You may also want to check to make sure there is no leaks or greae getting on the pads/drums. that will make the brakes lock up inder normal stopping.

As for the hot brakes. I also feel there is something holding the brakes line the rubber hose, or the wheel cylinder.

jack the car up, spin the tire, then pump the brake a few times and see if the wheel is still free. If it's hard to turn after pumping the brakes, I would replace the hose from the frame to the rear.

Perhaps a moderator will move this thread to the Brakes and Suspension forum.

1. Just because the brake hose allows fluid flow TO the brakes does NOT mean that fluid can readily flow back into the master cylinder. Sometimes the hose fails in such a way that it becomes a "check valve" allowing fluid to only flow one direction.

2. Is the master cylinder FULLY RETURNING to the at-rest position? If you look in the top of the master cylinder (cover off), and have a helper just "tickle" the brake pedal, do you see a little geyser in BOTH reservors?

3. Be aware that the park brake adjustment is separate from the service brake adjustment--and they BOTH need to be correct. Do the service brake adjustment FIRST, making SURE the shoes come to rest on the anchor pin at the top of the backing plate. Then do the park brake adjustment.

4. Wiped-out rear wheel bearings can cause problems with the drum-to-shoe alignment--and it's very common for the bearings to be so terrible that they've cut a groove into the axle shaft, too.

You said you just changed the master cylinder. Make sure you have adjusted the rod that activates the master cylinder and you have the proper pedal play.

no they bleed great when pushing brake peddle
That doesn't mean the rear brake hose isn't bad. Like was already mentioned, when these hoses get old, they can act like a check valve, allowing brake fluid to flow one way but not the other.

The fluid pressure when you apply the brakes is quite high which overcomes the blockage in the hose.
When you release the brakes however, the fluid pressure created by the brake shoe return springs is much lower, and the blockage in the hose stops the fluid from returning. This leaves some residual pressure in the system and the brakes stay applied.

I've seen this happen more than once, my own car included.

I'm in the camp with what's already been posted. But I would also yank the drums and do a visual for leaks and make sure nothing is broken or missing.

Is it possible you are having so much fun leaving the car show you are on both the gas and the brakes at the same time? If so, the hot brakes and resultant tire smoke are normal. :)