Have a 93 that has a strange problem I have a right rear brake that grabs or locks up after the truck sits for a period of time,sometime it will act as if I still have my foot on the brake when I dont and then it releases . I t will do this several times and then for the most part its ok but it will do it at random. Now Im a retired dealer tech over 35 years GM and Chrys stores never ran into a prob like this now its not master cyl or the rubber brake line going to the rear axle as only the left side locks up not the right . Ive asked my friends in the dealers they never had this come up. Ive done what is called a rear brake service took the drums off just dust in there cleaned with brake cleaner as Ive always done ,no leaks wheel cyi not leaking axle seal not leaking dry shoes have lots of lining left drum looks good. Thinking is wheel cyl sticking? best guess but since Im on disability dont have loys of extra money cant afford to start hanging parts till I fixed it so Im wondering if anybody has had this prob the truck is two wheel drive . Thanks

 

Do you use your parking brake? Could the brake cable housing have grit/rust causing excess friction? Otherwise I think your guess of the wheel cylinder is a good guess.