Usage:
793 (3SJ),
793B (1HL) Trucks
Description of Change: The hydraulic system can experience instability when the hoist cylinder is in the second stage. The instability can be eliminated by adding a fitting with an orifice in the hoist lines group and backing out the screw in the counterbalance valve.
Adaptable To: The 9X-6639 Fitting with the orifice is effective with 793B (1HL178) Truck. Resetting the counterbalance valve screw is also in effect. Both changes can be added to earlier 793 and 793B Trucks. Use the method that follows to add the fitting and reset the counterbalance valve.
Illustration 1. Location of the 2A-6474 Hose Assembly in the 8X-0232 Hoist Oil Lines Group
1. Disconnect the 2A-6474 Hose Assembly (1) in the 8X-0232 Hoist Oil Lines Group at location (A).
2. Install a 9X-6639 Fitting and 3J-1907 Seal where hose assembly (1) was remove from. Connect the hose assembly (1) to the fitting.
Illustration 2. Location of the screw in the 6E-0919 Counterbalance Valve Group.
3. Turn screw (2) in the 6E-0919 Counterbalance Valve Group counterclockwise 2 1/2turns.
After the 9X-6639 Fitting has been installed and the counterbalance screw turned out 2 1/2turns, the rod end pressure should be 5230 to 6200 kpa (750 to 900 psi) at high idle with an empty body.