TM 9-2320-209-20-3-4 19-18. REDUCTION DRIVE CHAINS ADJUSTMENT (TRUCK M764). TOOLS: 9/16-inch wrench 1/2-inch wrench (2) 3/4-inch wrench 6-inch ruler 18-inch straight edge SUPPLIES: None PERSONNEL: One EQUIPMENT CONDITION: Truck parked, engine off, handbrake set. a. First Reduction Drive Chain. FRAME 1 1. Using 9/16-inch wrench, unscrew and take out screw (1) and flat washers (2). 2. Using 1/2-inch wrench, unscrew and take out screw with flat washer (3). 3. Take off cover (4). GO TO FRAME 2 19-95