What makes a brake lock up?
 

I have original power drum on a 68 and had new wheel cylinders installed a while back. Now if I apply any real pressure to the brake pedal the right rear wants to lock up completely. To slow down I have to barely push it and downshift. It’s locked up on me a few times.

Try screwing the self adjuster in some, they could have left it a bit too tight.


Frank

Also could be wet shoes from leaking cylinder or axle seals.

Another possibility is the brakes on the other wheels are set up too loose, so that wheel is the first to grab. It's worth checking them all. One other thought is some of the brake cylinders may be gummed up and are sticking.

Typically for drum brakes, you adjust the star wheel so you can just hear a slight drag of the shoes against the drum. Make sure all four wheels have the same amount of drag.

I think it is the forest to grab kind of like it’s the only one working.

I had the same problem after my car sat about 8 years while I was away overseas.
I completely drained the entire hydraulic system and used new/fresh brake fluid. I had the drums checked for thickness and then had them turned/machined and they were perfectly round with no warpage.

I then replaced the old shoes and made sure the new shoes were put in the correct positions. The forward facing shoe is different from the rear facing shoe.

Removed and cleaned the adjuster and properly lubed it.

The shoes were then adjusted with the newly cut drums on until there was a very slight drag on the drum as it was rotated. Put the rubber seals back in place and put the wheels back on.

My car has front discs, so I did not have to adjust the front.

Got it back on the road and the lock up problem was gone.
While you have the car with both wheels off the ground, it is a good time to adjust the parking brake.