2010 Chevrolet Silverado 1500 Regular Cab Owner's Manual - Page 75

To move the adjuster down for the regular and crew cabs, squeeze the buttons (A) on the sides of the height adjuster and move the height adjuster to the desired position. On the extended cab, push down on the release button (A) and move the height adjuster to the desired position. Regular and Crew Cab Extended Cab You can move the adjuster up just by pushing up on the shoulder belt guide. After you move the adjuster to where you want it, try to move it down, without squeezing the buttons for the regular and crew cabs, or without pushing the release button for extended cabs, to make sure it has locked into position. 2-33