rear wheel problem

i just remembered something that happened to me a few months ago when i took my truck apart to restore it (73 c-10 cheyenne). i had taken the box off the previous day and decided to see if i had posi or not. after a few good burnouts with both wheels spinnin, i determined that indeed i did have it, but heres where the problem started. i was power-braking to make the wheels spin, and after the last one, the right rear wheel would lock up with even the slightest pressure on the brake pedal, and it would just drag that wheel along as the others were still rolling normaly. i either had to barely slow down or just let it drag, very annoying indeed.

what do you all think is wrong with it?

i put new stainless steel brake lines and also new hoses on the frame after i painted it; with everything, including the cab/body, engine, and tranny, removed. however, i left the original proportioning valve in place.

could it be the proportioning valve that is the culprit? after the winter hibernation, i will complete the restoration in the summer and am not looking forward to working on the rear brake components as of now.

any ideas?

re-adjust rear brakes

Could be leaky wheel seal (contaminated brake shoes)? Gear oil makes shoes stick.