check the spring on the rear brake adjuster on the rear of the hub, tend to find they can be broken or lost its compression and the brake leaver fails to return, same for a front wheel with drum shoes . another thing is the cable snagging inside the cable sheath where its become rusty and sticking.
Failing that, you'll have to have the wheel off, shoes off, struggle to get the main pin out, clean it, grease it, put it all back together again.
