97 ram 4x4 rear brakes locking ?

97 1/2 ton 4x4.

pedal feels the same as always but applying normal brake pressure on the pedal and the backs lock right up.

havent pulled the drums yet.

if its not an adjuster problem. would it be more likely an abs or master cylinder issue?

I've had this happen on two different vehicles. One the shoe lining litterally started flaking off (in big chunks--el cheapo brake shoes)
The other was a leaking axle seal and the resulting oil soaked brakes.

Pull the drums, I think you'll get your answer not matter what the cause.