TM 5-3895-346-14
STEERING CONTROL
POWER STEERING
There is no filter in the Orbitrol. Drain and replace as much of the oil as possible. Crank the pump over by
hand to exhaust oil from it and swing the cylinder through a full travel; but do not forcibly rotate the Orbitrol
steering wheel if a dirty fluid is suspected. Refill the system with clean oil, run the system briefly, recheck, and
refill as necessary to obtain proper fluid level. Operate the system for a short time to determine whether a
correction has resulted. It is sometimes less costly to rinse and reclean the system twice than to completely
tear down and reassemble a unit and the clean fluid will definitely protect all of the components of the system.
In the functional check, also determine that the actuating cylinder achieves full travel without hesitation. If the
cylinder seems to pause in its travel while it should be moving smoothly, this may indicate that it contains
trapped air. In filling and refilling a system, it is sometimes necessary to lift the vehicle weight off the steered
axle or to remove the cylinder and hold it in a position so that the ports are uppermost. In this position air will
be bled back to the system reservoir and effectively exhausted from the system at the reservoir vent. During
this inspection, determine that the mechanical or other limit stops at the axle are functioning properly. Proper
wheel alignment is every bit as important on power-steered vehicles as on any other to insure satisfactory tire
life and geometrically true steering.
Inspect to insure that the system has adequate power. Some machines are designed so that they cannot be
steered unless they are rolling. Most, though, will steer completely while standing still on a smooth, hard
surface. If there is an indication of hard-steering, this can indicate either a reduced oil flow to the control or a
reduced system relief pressure.
Adequate oil flow under all conditions can best be checked by timing the full travel of the cylinder with the
steered axle unloaded and loaded. If there is a great difference at low engine and slight difference at high
engine speed, this may indicate a defective pump drive. Adequate oil pressure can only be determined by
connecting a pressure gauge (2000 psi full scale recommended) at the pump outlet port or at the IN port of the
Orbitrol. With the engine running at a medium speed, turn the steering wheel to one end of the travel and hold
the cylinder at the travel limit just long enough to read the pressure gauge.
CAUTION
Never hold a system at relief pressure for more than a few seconds at a time.
Longer operation at relief pressure can overheat most systems quite rapidly. The
pressure relief valve is a protection for all of the various parts of the steering
system. There is no pressure relief in the Orbitrol. Power steering pressure relief
valves are usually located in the power steering pump or flow control valve or very
near the discharge line of either of these. Check or adjust to the vehicle
manufacturer's recommended pressure setting.
If the system is reported to operate extremely hot, connect a pressure gauge as above and operate the engine
at near full throttle. Rotate the steering wheel slowly in each direction and bring the wheel to the position that
shows the lowest pressure reading. This places the control section of the unit in neutral. Then turn the steer-
ing wheel to a limit stop and hold it there for one to two seconds. Release the steering wheel gently and watch
the gauge.
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