Have 2002 suburban back passenger disc has a 1/4 grinding down as if brakes r not catching equal only on this disc all other r good

Your calipers are not breaking equally. Best thing to do is replace BOTH calipers, rotors and pads. You stand the risk of losing control in wet weather.

There is a pressure equalizer valve that may not be working. Have a brake shop test the problem brake to make sure that is the problem. What do you mean by it is 1/4 grinding down? Is the front of the pads worn only? There mat be something preventing the pad from moving forward equally. Sometimes it is a cotter pin in the way, or just a sticky piston. The brake shop should know what the issue is and fix it. No need to replace everything. Make sure it is a good shop, not one that will only sell you all new components just to make money off you. If you go to the manager ans tell him to make sure the pressure to the calipers are equal, or to make sure there is nothing preventing the pads from making equal contact, you'll sound like you have some knowledge and it may keep him from selling you a muffler bearing.