GENERAL SUSPENSION TROUBLESHOOTING INFORMATION
A PRESSURE CHECKS: The 2,800-2,900 psi (19,306 - 19,996 kPa) maximum suspension system
pressure is controlled by an adjustment on the compensating pump. This adjustment should always
be checked prior to performing suspension system pressure checks. The suspension system pressure
checks can then be performed as specified in the troubleshooting procedures.
B SUSPENSION SYSTEM RELIEF VALVE: The sole function of this valve is to protect the suspension
hydraulic circuit in the event the pressure control device on the pump should fail. This valve is set to
open at 3,700-3,800 psi (25,512-26,201 kPa).
C DESCRIPTION OF THE SPRUNG SUSPENSION CIRCUIT: When the SPRUNG/UNSPRUNG
control lever is in the SPRUNG position, the operator has no control over the suspension. The height
of the vehicle is automatically controlled by leveling valves in the No.1 and 4 actuators. Each No.1 and
4 actuator and its paired No. 2 or 3 actuator is independent of the other three corners (fully independent
suspension). Therefore, the SPRUNG suspension system can be considered as consisting of five
major areas as follows:
The right rear pair of actuators.
The left rear pair of actuators.
The right front pair of actuators, with the right front bump stop cylinder.
The left front pair of actuators, with the left front bump stop cylinder.
The power system: pump, suspension relief valve, SPRUNG/UNSPRUNG valve,
and the main accumulator.
When the suspension will not raise, the most probable cause is excessive internal leakage
in one or more components. The troubleshooting procedures eliminate these major areas from the
circuit one by one to locate the fault.
D DESCRIPTION OF THE UNSPRUNG SUSPENSION CIRCUIT: When the SPRUNG/UNSPRUNG
control lever is placed in the UNSPRUNG position, the operator assumes control of the four front
actuators. However, the four rear actuators remain in an automatic mode. Hydraulic valves in the No.1
and 4 actuators shift position to cause all four rear actuators to share a common pressure line (the two
rear No. 4's are no longer independent). This is necessary so the front of the vehicle can be tilted (one
front side of the vehicle lowered more than the other side). Therefore, problems can develop in either
the front or rear areas of the suspension hydraulic system that could affect performance in the
SPRUNG mode only, the UNSPRUNG mode only, or both modes.
OPERATIONAL VEHICLE: The vehicle should be considered operational if it will rise within 2 minutes
of engine start and will stay up long enough to perform its mission.