75 A-body 7 1/4" rear original drum brake. 10" I think. Keeps getting tighter, now I'm driving with brake applied. I backed off on adjusters a coupla weeks ago so drums would turn freely. Now has tightened up badly again.

Why is this happening?

If you or someone else just had them apart then the self adjuster may be installed wrong. Either post pics or veiw a service manual and you will likely see the problem

I agree sounds like adjusters are backwards.Most times the arms are marked left and right.Just remember left is drivers side.Rocky

I will try to post pic. Looks correct to me. See anything wrong? Drum was LOCKED.

Sorry image rotated 90*. This is driver side. No problem on other side.

Check to see if the brake hose is collapsed/kinked. Could be collapsed inside. This would not allow fluid to return to the m/c hence, fully expanding the brake shoes against the drum.

If it was the hose both would be locked as its the rear and both feed off the same hose.Check the adjuster and make sure its a L.Been a while since I played with them.Rocky

Mmmm, aren't they split to each side from the brass dist block mounted on top of the rear?

Steel line to the whl cyls from the block.From what he says its the adjuster getting tight.If the line was collapsing it would pressure both.The little difference in length of the steel lines really wouldnt matter.Rocky

i had the exact same thing happen on my '81 d150. i had freshened up the rear brakes and one side kept tightening up 'till it was locked and so hot i couldn't touch the wheel. turned out to be the guide for the adjuster cable was slightly bent and would cause the adjuster to tighten up when driving. it's the steel piece that looks like a 1/3 or 1/2 slice of pie that the cable routes around. i was 2 hours into a road trip when i found the problem that had been bugging me for weeks. i was on the side of the highway and a vicegrip solved the problem. it was a new part by the way. check all the small parts for any bends, kinks or warpage. good luck

Thanks for replies.

It is the adjuster ratcheting tighter and tighter. I am back together now and rolling along nicely. Wanna drive it some before weather gets ugly. If/when it tightens again I will check for free movement of that cable, and try to post a better pic next time.

The adjusters are side specific as well as brake size specific.

In all probability you have an adjuster on the wrong side or a left wheel adjuster on a right wheel (or vise Versa).