785C CAT PURGE & CHARGE FRONT SUSPENSION

This is one of my job as a maintenance mechanic, I'll share it with you. How to purge and charge front suspension of 785C Catterpillar OHT.

Unit Position should be on flat and level
ground and coast the machine to a gentle stop
whitout using the brakes.Please prepare area or space +/-2 m from left
& right side of truck.Install four wheel chock on rear tires. Turn off master battery disconnect switch, Attach a “TAGGING & LOCK OUT” tag at the battery isolation box and Attach personal danger tag.

Prepare hydraulic jack as required, Prepare for correct tools to charging and make sure the Nitrogen is used. Never used Oxygen.

Before you perform any repairs, please read all safety procedure and used MSDS system to get
precaution on safe work. Connect charging chucks and hose at both front suspension. Open valves and drain oil and nitrogen charge into suitable catch-tank until cylinder have bottomed completely. Once the suspension are fully retracted wait a further 5 minutes until oil and nitrogen stops.

Check the relief valve for the grease. The relief valve may need to be removed in order to clean the old grease from the valve. Connect oil line to oil supply into the charging chuck for both front suspension. Mark zero position for reference line on the top edge of the axle and line up with zero reference at the steel rule with paint pen. Adjust the air pressure on the regulator. The air pressure must not exceed 860 kPa (125 psi). Inject oil into the suspension cylinder until the suspension rod has been extend about 25 mm from reference line (reference line on the chrome lines up with reference line on the ruler).

WARNING
Release pressure in hoses before removing

Using suspension charging tool, connect nitrogen charging lines to both front cylinder. Open Nitrogen bottle valve. Adjust the regulator pressure slowly. Put the Jack under the frames and raise the truck until the rear struts are fully extended. Re-adjust the Nitrogen regulator to appropriate pressure and charge both of the suspension.

Using VIMS display to check parameter codes 720 and 722 have reached this pressure. Once both cylinder have stabilized at this pressure, close off the shut off valves and nitrogen tank. Release the pressure in the line, Remove all tool and install valve caps. Lower truck off the stands then move the truck and come to a smooth gradual stop. Check the height of the chrome rod and record the height. Specification 254 +/- 13 mm (10 +/- 0.5 inch). Measure ride height suspension after charging. If the height of chrome rod showing still below the specification , restart from step 10, but do it on one cylinder at one time, with 5 psi added on the last known pressure. Record the last pressure and ride height. Calibration the payload after adjustment the suspension.