CYL GP- 4Z5958 - Caterpillar

Pressurized system!The hydraulic tank contains hot oil under pressure. To prevent burns from the sudden release of hot oil, relieve the tank pressure with the engine off by slowly turning the cap approximately 1/8 of a turn until the cap reaches the secondary stop.
Illustration 2 g02275615
Filler cap
(A) LOCK position
(B) PRESSURE RELEASE - START position
(C) PRESSURE RELEASE - END position
(D) OPEN position
Release the pressure that may be present in the return hydraulic circuit with the following procedure. Refer to Illustration 2 for filler cap positions.
Turn the filler cap counterclockwise, with no downward force applied, and move the arrow from position (A) to position (B).
Release the pressure for a minimum of 45 seconds by moving the arrow from position (B) to position (C).
Push the center of the filler cap down. Without tilting the filler cap, move the arrow from position (C) to position (D).
The hydraulic tank pressure is relieved. The filler cap can now be removed if needed.
Tighten the filler cap on the hydraulic tank to position (A).
After the pressure is relieved, tighten the filler cap.
Illustration 3 g03760097
(2) Hose
(3) Clamp
Open the engine hood. Loosen clamp (3) and disconnect hose (2) from the radiator.
Illustration 4 g01221303
(4) Cover
(5) Bolts
(6) Washers
Remove cover (4), bolts (5) and washers (6).
Illustration 5 g01362818
(7) Hose
(8) Screw
Put the other end of hose into a suitable container.
Slowly loosen screw (4) by a maximum of 1/2 turn. Loosening screw (4) allows the hydraulic oil in the boom circuit to drain into the container. The boom will now start to lower.Note: Refer to Operation and Maintenance Manual, "General Hazard Information" for information on containing fluid spillage.
Make sure that the work tool has lowered all the way to the ground.
Connect hose (2) to the original position on the hydraulic tank and install the fill/vent plug securely.
Close the engine hood.After completion of the manual boom lowering, make necessary repairs before you operate the machine again.Note: For additional information, consult your Cat dealer.Machine with a Boom Lowering Control Valve
Boom load may cause cylinder oil pressure to reach relief pressure of the boom lowering control device when the boom is supported by one cylinder. Boom can lower suddenly, causing possible injury or death.To avoid possible injury or death, be sure no one is under or near the work tool before manually lowering the boom.Keep all personnel away from the boom drop area when lowering the boom with the engine stopped.
If the engine is shut down or the hydraulic system is disabled, the operator can still lower the boom. Use the following procedure if the machine is equipped with a boom lowering control valve.
Illustration 6 g06235792
(1) Locknut
(2) Check valveThe boom lowering control valve (if equipped) is installed on each of the boom cylinders. The boom lowering control valve allows the operator to lower the boom if the engine is stopped. The boom lowering control valve also prevents the sudden descent of the boom if there is an oil leak in the hydraulic line of the boom.
Loosen locknut (1) of the boom lowering check valve.
Slowly turn check valve (2) counterclockwise until the