Usage:
777 (84A),
777B (4YC),
777C (4XJ),
777D (3PR) Off-Highway Trucks
Reference: Service Magazine; June 10, 1996; Page 11; "New And Modified Hoist Cylinder Valves And Plates Available To Soften Landing Of Body" for 771C, 775B Quarry Trucks and 769C, 773B Off-Highway Trucks.
A Hoist cylinder valve is available which can be modified to control body down impact speed. The 156-8571 Valve features a smaller orifice diameter of 5 mm (0.20 in) and is a direct replacement for the 3G-2326 Valve. The 3G-2326 Valve is factory installed and features an orifice diameter of 10.31 mm (0.406 in). The smaller orifice further restricts the oil flow from the hoist cylinder to the tank when the truck body is being lowered, slowing the speed of the truck body and reducing impact of the truck body on the frame. The 156-8571 Valve and 3G-2326 Valve are used in the 8J-8924 Cylinder Group and are adaptable to 777 (84A), 777B (4YC), 777C (4XJ) and 777D (3PR) Off-Highway Trucks.
Procedure To Control Body Down Impact Speed On Certain Off-Highway Trucks
1. Measure the average time it takes for the truck body to move from UP position to DOWN position with the original 3G-2326 Valve installed. This average time will establish the baseline body down float speed (+ 0 seconds).
2. Refer to information listed in chart below. Modify orifice diameter on 156-8571 Valve. Add baseline average time to corresponding approximate body down float time and this equals the new body float time and impact speed.
NOTE: Modifications to the 156-8571 Valve orifice diameter will directly influence cycle times.
3. Install 156-8571 Valve into 8J-8924 Cylinder Group, on both sides of the machine.
NOTE: Two 156-8571 Valves are required for each machine, orifice diameters must be equal.
4. Raise and lower truck body to test body down impact speed.
5. If necessary, continue to modify Diameter A by 1 mm (0.39 in) increments until desired body down impact speed is achieved. Diameter A should not exceed 10.31 mm (.406 in).
NOTE: In order to decrease body down impact properly, the 9J-1234 Body must be oriented so that the pressure tap port side is facing away from the cylinder body. The 156-8571 Valve's poppet face must also point away from the cylinder body.
