Drum Brakes won't release

[Eotku]

I bought a 1970 chevy blazer a couple of months ago and today was the day I got it on the road. After driving it a few miles to work I noticed that the brake peddle was pretty much staying at the top of the stroke. When I started driving it home I could tell something was wrong. When I was in a parking lot and tried to backup I noticed that the truck wasn't wanting to roll. It felt like the parking brake was on but it wasn't. I only had a couple of miles to go and so took back streets to keep the speed low. The more I drove the hotter the brakes got. When I got home the front brakes were smoking hot. Rear were hot too but not smoking. I was only able to push the peddle down about 3/4 of an inch. When I first got the truck I did take all the drums off and looked at the brakes and they looked worn but OK. I did adjust them but wasn't sure how loose they should be. I adjusted them so the drums would just barely go on with hand pressure. So what are your thoughts? Master cylinder? Wheel cylinders? Adjusted too tight. I appreciate any insight you may have.

[67 chevelle]

actuator rod in master cylinder is to long , usaly adjustable , sometimes a2 washers behind it fixes it if you cant adjust rod or booster

[68gmsee]

Many years ago, I had the same problem with rear brakes. In my case it turned out to be a severely swollen (internally) rear rubber brake line. Pressure would allow brake fluid to the brakes but there was not enough spring pressure to allow fluid to return so the brakes stayed engaged until they cooled and gradually returned to normal.

Rubber lines will swell up after years of use and you can't tell by looking at them from the outside. I replaced them all to be on the safe side.

To determined if that's the cause loosen the brake bleed valve when they're locked to see if they loosen up. Otherwise, check the brake booster and push rod as 67 chevelle mentioned.

[Tx Firefighter]

Swollen brake hoses guaranteed. I've seen it many times.

They swell shut on the inside. They'll pass the ultra high pressure from the master cylinder when applying the brakes, but the springs in the drums aren't strong enough to retract the wheel cylinders and force the fluid back through the restricted hoses when you release them.

If you want further proof, next time it does it, slide under there real quick and crack open the bleeder valves for a second. The fluid will squirt out under a lot of pressure rather than dribble or drizzle. It's the springs retracting the brake shoes that causes the pressure. You'll also hear the brake shoes relax away from the drum if you're in a quiet environment.

[Eotku]

Thanks for the suggestions. I will be working on it this weekend and let you know what I find. LOVE having this blazer. First toy I have had in a long while!

[Eotku]

I parked the blazer at the top of my sloped driveway until the brakes cooled down. So after a couple of hours the brakes have cooled down and the brakes now seem fine. I will adjust the brakes this weekend and see if that helps. I am resisting doing too much as I am wanting to upgrade the axles this summer. Wanting to go to 3.73 front disc at the least and maybe also 3/4 ton as well. At that point I would redo it all. For now just want to make it drivable. If the adjustment doesn't work I'll replace the hoses as well. FYI I drove it home over 30 miles and didn't have any issues with the brakes.

[Eotku]

To Clarify I drove it home 30 miles when I bought it. Today It was only 5 miles to where I work and the brakes started to have issues within 2 miles.

[imjeff]

Replace the rubber lines. You will revisit your issue again if you don't. It's not a pile of cash.

[BLT gmc]

X all the above

[Wrenchbender Ret]

I would look at the Master cyl. rod first like 67 says. If the rod does not let the piston come back all the way it does not open the compensating port.