Chapter 9 Steering Systems 185
In a power steering system, pressure is created by a
pump and transmitted to the steering gear or, in a few
cases, a separate power piston. This pressure is used to
help the driver move the wheels. Pressures in a power
steering system can rise to over 2000 psi (13,450 kPa) dur-
ing hard turns.
Power Steering Fluid
The average power steering system contains less than
two pints (0.95 liters) of hydraulic fluid. A few systems use
slightly more. This fluid must transfer pressure, lubricate
parts, and remove heat. Most power steering fluid is
intended to last the life of the vehicle, providing lubrication
without breaking down into sludge or acids.
Many older power steering systems used automatic
transmission fluid as hydraulic fluid. Newer systems,
however, are filled with special power steering fluids.
These fluids contain additives designed to increase the
smoothness of power steering system operation and
prolong the life of the power steering parts. Specific fluid
requirements vary from one manufacturer to the next. Due
to the extreme forces placed on the fluid, it is important
that the correct fluid be used.
Power Steering Reservoir
The power steering system must be full of fluid at
all times. Any air that enters the system will cause
malfunctions. The power steering reservoir stores extra
fluid for use by the other system components. Some reser-
voirs are installed around the pump assembly, Figure 9-39.
The pump draws fluid directly from the reservoir. A large
O-ring is used to seal the pump and reservoir mating
surfaces. Other reservoirs are separate from the pump and
are connected by low-pressure hoses, as in Figure 9-40. A
filler cap installed on the top of the reservoir allows fluid to
be added when necessary.
Power Steering Pump
The engine operates the power steering pump.
A pulley on the engine crankshaft turns a belt that turns a
pulley on the power steering pump, Figure 9-41. The
engine may have to provide as much as 5 horsepower to
create pump pressure during maximum power assist.
Most power steering pumps are vane-type pumps,
Figure 9-42. This type of pump has an internal chamber
with suction and pressure sides. Flat metal vanes turn
inside the chamber to draw in and pressurize fluid. To keep
the vanes in contact with the chamber walls, pressure is
directed to the area at the center of the pump. This pressure
enters behind the vanes and pushes them against the walls
of the chamber.
Refer to Figure 9-43 as you read the following section.
In the suction chamber, the vanes move apart and the area
between the vanes increases. This creates a partial vacuum
that sucks fluid into the chamber from the reservoir. The
fluid is carried around to the pressure side of the chamber.
On the pressure side, the area between the vanes becomes
smaller and the fluid is pressurized. The pressurized fluid
then exits to the other parts of the system.
A similar type of pump is the slipper pump. The
operating principles are similar to those of the vane pump,
but spring-tensioned slippers are used instead of vanes.
The spring tension keeps the slippers in contact with the
pump wall. Figure 9-44 shows a typical slipper pump. An
older design uses rollers in place of the slippers.
See Figure 9-45.
A few vehicles have dual gear power steering pumps.
The dual gear pump, Figure 9-46, creates pressure using
two gears. As the gear teeth move apart on one side of the
pump housing, they create a suction that draws in fluid.
The fluid is carried around with the pump gears and then
compressed as the gear teeth move together.
Some late-model vehicles are equipped with hydro-
boost brake systems. In these systems, the power steering
pump produces power assist for both the steering system
and the brake system.
Cap
Cap
Cap
Reservoir
attached
to pump
Reservoir
contains
pump
Reservoir
contains
pump
Pump
bolt
Pump
(submerged type)
Line connections
Pump
(submerged type)
Pump
(nonsubmerged type)
Figure 9-39. Three different styles of power steering pumps with fluid reservoirs installed around them. (General Motors)