TM10-3930-660-20 18-6. MAIN CONTROL VALVE ASSEMBLY - ADJUST/REPLACE (Cont’d) f. g. When desired relief pressure obtained, release boom hoist lever. Hold adjusting screw in position and tighten jam nut Install acorn nut (9) . 4. ADJUST MAIN RELIEF VALVE TO BETWEEN 2,750 AND 2,850 psi. is (10) . a. b. c. d. Operate boom extend, retract, hoist or lower function until hydraulic oil is passing over relief  valve. Continue to hold hydraulic lever in that position so oil passes over relief valve during relief valve adjustment. Turn adjusting screw counter- clockwise (out) until pressure on gauge reads between 2,750 and 2,850 psi. Release hydraulic function lever. Hold adjusting screw in position and tighten jam nut (4). Install acorn nut (3). 5. STOP ENGINE, TM10-3930-660-10. Hydraulic oil in the system can be under pressures over 3000 psi with the engine OFF. ALWAYS relieve  pressure  in  hydraulic lines before attempting to remove any component in the hydraulic system. With engine OFF, starter switch in RUN position, and MLRS attachment on the ground, move control levers through all operating positions several times to relieve line pressure. Relieve pressure in hydraulic oil tank by loosening filler cap very slowly. Failure to follow these precautions could result in serious personal injury. 6. 7. 8. REMOVE PRESSURE GAUGE. Unscrew pressure gauge from main relief valve plug assembly port (2). INSTALL MAIN RELIEF VALVE PLUG ASSEMBLY. Screw main relief valve plug assembly (1) into port (2) and tighten. REPLACE TRANSMISSION COVER, PARA.  16-6. 18-28