TM10-3930-660-20 18-24. BOOM EXTEND AND  RETRACT CHAINS - INSPECT/ADJUST This task covers: a. Inspect/Adjust Initial Setup Tools Reference Tool Kit, Automotive Mechanics TM10-3930-660-10 Equipment  Condition Vehicle parked on level ground. INSPECT/ADJUST 1. FULLY EXTEND BOOM, TM10-3930-660-10. 2, PLACE BOOM Adjusting  the retract  chain IN HORIZONTAL POSITION. tension of the boom will also adjust  the tension in the boom extend-chain. 3. MEASURE RETRACT CHAIN  SAG (1) AT MIDDLE OF INTERMEDIATE BOOM SECTION. Chain sag (1) should be approximately 3-1/4 to 3-1/2 inches (83 to 89 mm) from top of chain to bottom of boom. 18-94