Group 25, Steering Column and Gear
SM 765, Nov ’06 Steering System Specifications and Description • 25-1-1
Specifications
Steering System Type: Hydrostatic power steering with
load sensing, dynamic signal neutral circuit.
Steering System Relief Pressure Setting: 10000 kPa (1450
psi)
Service Intervals
Check the steering system relief pressure annually or after
every 2000 hours of operation. Make a visual inspection
of steering control unit hydraulic fittings periodically to
ensure that the fittings are tight with no leakage.
Fastener Torques
Steering Handwheel Nut: 35-45 N⋅m (25.5-33.5 ft-lb)
Description
All truck models have a hydrostatic power steering sys-
tem, which is supplied with oil pressure from the main
hydraulic pump. The steering hand wheel operates the
steering gear (steering control unit), which directs oil flow
to the steering cylinder on the steer axle. A steering sys-
tem pressure relief valve is built into the steering control
unit to prevent over-pressurization of the steering system.
The pressure relief setting can be tested by installing a test
fitting install Quadrigage at pressure inlet of steering gear.
The power steering gear is a remote positioning control
valve that senses the input signal from the steering hand
wheel, multiplies this signal to assist in reducing the steer-
ing effort, and causes the steering axle to turn the wheels
to the desired position by supplying hydraulic flow to the
steering cylinder.
The steering gear is connected to the bottom of the steer-
ing column. When the steering hand wheel is turned, it is
linked mechanically to the steering gear spool and causes
this spool valve to shift from its closed neutral position to
a “turn” position that allows oil under pressure to flow to
the steering cylinder.
When the steering hand wheel stops turning, centering
springs in the valve automatically center the spool, stop-
ping the flow of oil to the cylinder.
The low pressure oil from the opposite side of the steering
cylinder is returned through the opposite port in the gear.
It is controlled by the same spool as the high pressure
port.
In the event of a pump failure, the steering gear can gener-
ate sufficient hydraulic power by movement of the steer-
ing handwheel to serve as a limited steering method. An
internal check valve automatically closes to divert this
generated oil flow to the proper port of the steering cylin-
der. The handwheel turning effort is considerably higher,
however, than with power steering.
Section 1
Steering System Specifications and Description
To Next Page
Loading...
