brakes sticking back wheels on 1999 GMC 3500 Pickup

changed ..porportion valve & mastercylender checked rear hose(ruber)butafter pulling it off dosent look bad should i chang hose or am overlooking somthing? when i slam on the brakes back wheels stay tight untill i tap pedal again

Asked by for the 1999 GMC 3500 Pickup
After replacing the rear shoes on my 2000 K3500 the rear brakes lock up. Every 2000 miles I need to back off the adjusters
2 more answers
Not clear what you mean? Diconnect the emergency brake cables.
This is not and answer but, I hope to clarify the issue. When coming to a stop, the rear drum brakes suddenly grab and lock up, will roll normally if released but, grab suddenly as in more than the brake pressure would account for.
My pals truck is doing this, I am telling him that I want to put a new master cylinder in it. The problem reminds me of some car I read about that the brakes had to be bled a certain way or the proportioning valve would get stuck in the wrong place. I have found no special procedure reference about this truck.