TRUCK SERVICE MANUAL
a. With the engine running above idle, shutoff valve
cap SE-1985-8 and plug the port using plug
open, read the gauge while someone turns the
SE19857. Leave the shutoff valve open, engine
steering wheel. If the correct pump relief valve
running above idle; from a straightahead position
pressure registers on the gauge when the
wheels reach the end of full travel, the hydraulic
approximately 1/4 turn to the left or until you feel
system checks satisfactorily, and it is not
pressure buildup; check the pressure gauge.
necessary to go any further with hydraulic check.
Approximately 1/4 steering wheel turn to the right
Trouble is probably mechanical or due to other
check gauge again. The specified relief valve
causes such as abnormal front-end weight.
pressure should register for both directions,
indicating the steering control valve is okay.
NOTE: System with a shuttle valve in the cylinder may
b. If the specified pressure is not reached, the valve
register a sharp dropoff in pressure at end of wheel
is faulty; we may have hard steering in either or
travel; this is normal.
b. If the specified relief valve pressure is not
c. Valve trouble is usually internal leakage--most
reached and steering is hard, our system is
often caused by worn seals. Rusting, pitting or
scoring of surfaces with which they contact affects
greatly the life of seals. Check these surfaces
when you disassemble a valve; minor damage
we must test the components to pinpoint the
can sometimes be touched up with crocus cloth;
place of trouble. Leave the pressure gauge and
noticeable rough surfaces require replacement of
shutoff valve installed, front wheels stationary.
2. Check the pump first:
d. Check for dirt and scoring; a valve must move
a. Gradually close the shutoff valve; pressure
freely and without sticking. Cleanliness and care
gauge should register relief valve pressure just
are a must when working on a steering control
before or just at closing of the valve. If it does,
valve. Forcing or abusing closely fitted parts of
the pump is working correctly.
any components will probably damage them
NOTE: Do not keep shutoff valve closed longer than 15
enough to requite replacement.
seconds; oil may overheat and damage pump and seals.
4. Assume in the first teat we found the hydraulic system
b. If the correct pressure does not register, the
was not maintaining enough pressure to give us power
pump is faulty. Trouble may be any of the
for steering, but our second test indicated the pump
following: seized or "frozen" surfaces, scoring on
was working property, Our third pressure gauge check
end faces of gears or housing, binding, scored or
told us the coiitrol valve was also working correctly,
damaged teeth, rotors or vanes, dirt or stickiness
This leaves only the cylinder as the point of trouble,
of flow control valve or pressure relief valve, a
providing no other troubles such as binding or friction
leaky pump shaft seal.
were missed in the previous checks. If not, we can
c. A hydraulic pump requires finely machined
conclude that our trouble is in the cylinder and
surfaces for operation. A clean workbench must
proceed to locate the point of failure.
be used for disassembly and repair. (Clean
a. Cylinder trouble is usually leakage--internal due to
wrapping paper makes a good, disposable
scored cylinder walls or broken piston rings, or
workbench top. ) Clean pump off with clear,
external around a bent, scored or binding piston
clean solvent before disassembly; blow dry with
rod or leaky rod seals.
clean air. Lint from wiping rags can destroy the
b. A shuttle valve sticking open will cause a loss of
exact fit required of some surfaces.
pressure too. If the cylinder has a shuttle valve, be
3. If the pump is okay, check the steering control valve:
sure to check it.
a. Disconnect the hydraulic hose at one cylinder
c. A cylinder functioning improperly cannot apply
port; cap the end of the hose using
sufficient power to the steering linkage. Hard
steering is the result.