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TM 10-3930-671-24
9.2. Steering Column and Valve
(Steering Gear)
Description and Operation ..............................................................................F-405
Steering Troubleshooting ........................................ .......................................F-405
Steering Column & Valve Mounting ................................ ...............................F-406
Description and Operation
NOTE
The nomenclature used in describing service
procedures for the power steering system
control components reflects the change in
technology of hydrostatic steering systems
as compared to manual steering systems,
and differs in some areas from that used in
the Service Parts system. In the Service
Parts Book and illustrations in this manual,
the steering column and valve assembly is
referred to as the steering gear assembly; the
steering valve (or steering control unit) is
referred to as the power steering gear box
assembly;
and
the
steering
column
is
referred to as the steering gear shaft
assembly.
The power steering control unit is a remote positioning
control valve that senses the input signal from the
steering handwheel, multiplies this signal to assist in
reducing the steering effort and causes the steering axle
to turn the wheels to the desired position by supplying
hydraulic pressure to the steering cylinder.
The steering valve is connected to the bottom of the
steering column. When the steering wheel is turned, it is
linked mechanically to the steer valve 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 handwheel stops turning, centering
springs in the valve automatically center the spool,
stopping the flow of oil pressure to the cylinder.
The low pressure oil from the opposite side of the
steering cylinder is returned through the opposite port in
the valve. It is controlled by the same spool as the high
pressure port.
In the event of a pump failure, the steering control unit
can generate sufficient hydraulic power by movement of
the steering 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 cylinder. The handwheel turning effort is
considerably higher, however, than with power steering.
Steering Troubleshooting
The following list of symptoms and possible causes are
the
most
common
steering
system
problems
encountered.
Troubleshooting Guide
1.
High number of handwheel turns
1)
Steering cylinder seal leakage
2)
Worn steering valve
2.
Handwheel steering effort too high
1)
Relief valve setting too low
2)
Axle load too heavy
3)
Defective steering valve
3.
Steering handwheel spins freely
1)
Air in system (cavitation)
2)
Low oil supply
3)
Defective steering valve
4.
Truck turns in wrong direction
1)
Hydraulic lines not installed correctly
5.
Handwheel kickback
1)
Check valve faulty (or not in system)
2)
Improperly timed steer valve
6.
Slow steer response
1)
Oil viscosity too heavy
2)
Defective steering valve
F-405
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