GM Service Manual Online
For 1990-2009 cars only

Inspect the linings every 9 650 km (6,000 mi) and any time the wheels are removed (tire rotation, etc.). Inspect the shoe and lining assemblies for wear by removing the brake drum. Replace shoe and lining assemblies when the thickness of any lining is worn to within 0.76 mm (0.030 in) of the shoe. Replace riveted shoe and lining assemblies when the lining is worn to within 0.76 mm (0.030 in) of any rivet head. Always replace shoe and lining assemblies as a complete axle set.