H40XL H50XL H60XL [A177]
This section has the description and repair procedures
for the steering housing and the steering control unit.
Additional information on parts of the steering system
are in the following sections: STEERING AXLE and
DESCRIPTION (See FIGURE 1.)
This section has a description and the repair procedures
for more than one brand of steering control unit. The
units are similar in construction and operation with hose
connections on the side at a manifold or valve block as-
sembly. See FIGURE 2. or FIGURE 4. Some manifolds
also have a relief valve.
The steering control unit is a hydrostatic unit that is con-
trolled by the steering wheel. The control unit is in-
stalled in a housing or on a bracket at the cowl and is op-
erated by the column assembly and steering wheel. The
steering control unit has a control section and a metering
The steering system is a hydraulic system that does not
have a mechanical connection between the steering
wheel and the steering axle. The control of the steering
is through a hydraulic circuit.
If the hydraulic pump for the steering system does not
operate, steering is still possible. A check valve permits
the steering control unit to control the steering cylinder.
The lift truck is difficult to steer when the steering pump
is not operating, but the steering control unit can operate
the steering cylinder and make steering possible.
OPERATION (See FIGURE 1.)
The steering control unit is a rotary valve operated by
the steering wheel. During the steering operation, the
steering control unit controls the direction of flow and
amount of oil that flows to the steering cylinder. The
steering cylinder in the axle actuates the steering linkage
to move the steer tires. Hydraulic oil returns from the
steering cylinder to the steering control unit and then re-
turns to the hydraulic tank.
Turning the steering wheel actuates three main par