My rear brakes locked up on my 1997 chevy suburban on 1997 GMC Suburban 1500

What would make the rear brakes lock up on my 1997 chevy suburban?

2 answers
Assuming you have rear drum brakes, you could have wheel cylinder issues, adjuster issues, hardware issues, axle seal oil leaks... A good inspection - soon - is in order.
does it have hub brakes on rear wheel cylinder probley leaking shoes are soaked with fliud replace wheel cylinder and shoes clean every thang with brake cleaner