Tires locking up on 2001 GMC Sierra 2500 HD

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As I am driving there is a bang (maybe truck is trying to switch into 4wd) and all 4 tires are locking up. I put a new transfer case in last year. Any ideas?
(1) Answer
it is the Ebrake on rear end
mine just went out
it explodes,clean out pieces and you will have to replace a seal
I just went around it and still have 3 brakes working