ARM 0878490 - Caterpillar

Illustration 1 g03717245
Right Side of Machine (1) Front-wheel assist solenoid (2) Front-wheel assist manifold (3) Port "P" (4) Minimum pressure valve (5) Port "T" (6) Flow divider valve for port "A1" and "B1" (7) Flow divider valve for port "A2" and "B2"On machines with the front-wheel assist system, front-wheel assist manifold (2) is located on the right side of the machine. This manifold is near the right tow point cylinder. The right side door provides additional access to this component.Note: The machine can be equipped with one of two front-wheel assist systems. The four-wheel drive system contains two front-wheel assist motors, and all-wheel drive system contains four front-wheel assist motors. The above illustration shows the front-wheel assist manifold (2) on an all-wheel drive system.The following components can be seen on the above illustration:
Front-wheel assist solenoid (1)
Port "P" (3)
Minimum pressure valve (4)
Port "T" (5)
Flow divider valve (6) for port "A1" and port "B1"
Flow divider valve (7) for port "A2" and port "B2" on all-wheel drive system onlyFront-wheel assist solenoid (1) is a proportional solenoid. The transmission ECM controls this solenoid through the relay driver module. When the transmission ECM determines that the front-wheel assist system should be operating, the ECM prompts the relay driver module to energize the solenoid. The output signal is based on machine speed.Port "P" (3) of the front-wheel assist manifold receives oil from port "B" of the front-wheel assist pump. Port "T" (5) of the manifold directs oil to the return manifold.Minimum pressure valve (4) will not allow oil to flow to the front-wheel assist motors until the pressure is greater than approximately 1000 kPa (145 psi). Flow divider valves (6) and (7) equally split hydraulic flow between the front-wheel assist motors. These valves act like hydraulic differentials.
Illustration 2 g03717252
Right Side of Machine (8) Port "B1" (9) Freewheel check valve (10) Port "A1" (11) Port "G3" (12) Port "A2" (13) Port "B2" (14) Freewheel control spool (15) Port "X" (16) Port "CD"Front-wheel assist manifold (2) is equipped with freewheel check valve (9) and freewheel control spool (14). A hole in the front guard (removed) provides access to these components when the right hopper wing is raised.Freewheel check valve (9) maintains back pressure in the case drains of the front-wheel assist motors when the system is not operating. This back pressure lifts the pistons off the cam to allow the motors to spin freely.Freewheel control spool (14) purges the back pressure from the case drains of the front-wheel assist motors when the system is operating.Ports on the front face of front-wheel assist manifold (2) include port "A1" (10), port "B1" (8), port "A2" (12) and port "B2" (13). These ports direct oil to the front-wheel assist motors. Port "X" (15) and port "CD" (16) are located on the left face of the manifold. Port "X" is the signal pressure port. The case drain lines from the front-wheel assist motors direct oil into port "CD". Pressure in the front-wheel assist circuit can be measured at the pressure tap