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STEERING SYSTEM
HOW DOES IT WORK?
1965 - 1977
Ford/Thompson Power Steering Pump
A basic working description of the Ford/Thompson Power Steering Pump, with attention to some of the model line differences and production variations.
In 1965 Ford introduced a new design power steering pump to replace the aging-design Eaton pump. Commonly called the Ford pump, it was a Thompson (TRW) design that Ford used until being replaced in 1978 by the C-II design pump. The new Ford pump was a totally different design from the old Eaton roller-style pump, but its biggest difference was that the fluid reservoir actually surrounded the pump mechanism, which was mounted inside.
BASIC CONSTRUCTION
The Reservoir is a metal can that surrounds the Pump Cartridge and holds the fluid used in the system. Not only is the fluid readily available to the pump, it also helps to cool the pump mechanism and dissipate heat through the can. The Reservoir slips onto the Front Housing of the Pump Cartridge and is sealed to it by a large rubber O'ring. The Pressure Fitting and sometimes a Mounting Stud protrudes from holes in the back of the Reservoir and are sealed by paper fiber and copper washers.
There are two basic designs of Reservoirs. In 1965 and 1966 Ford used Reservoirs with large diameter Filler Tubes, similar to the tubes used on the earlier Eaton pumps. In order to make the Ford pump fit easier on numerous engine applications, in 1967 Ford went to a small diameter Filler Tube that was used on most Ford pumps through the late 70's. During production of both styles of Reservoirs, there were also many differences in Pressure Fitting style and location, Mounting Stud application, and Return Nipple length and direction. By varying these factors, Ford was able to fit the Ford pump to everything in their car and truck line.
Basic Ford Pump Cartridge
Reservoir - 1965/1966 Mustang V8 w/AC
Reservoir - 1965/1966 Mustang V8 w/AC
Reservoir - 1967/1969
PUMP CARTRIDGE
BARE
RESERVOIR
1965-1966
LARGE
FILLER
TUBE
RESERVOIR
1967-1978
SMALL
FILLER
TUBE
RESERVOIR
BASIC OPERATION
The engine driven Pulley turns the Input Shaft which spins a Cam Pack assembly inside the pump. This Cam Pack takes fluid in from a slot in the side of the Pressure Housing and compresses it in the end of the Pressure Housing. Excess pressure is bled off by the Pressure Valve and fluid is returned to the Cam Pack. The pressurized fluid exits the Pressure Housing through the Pressure Fitting and is carried through the Pressure Hose to the Control Valve. From here is is distributed to the Power Cylinder to turn the car or returned to the Reservoir by the Return Hose.
The Cam Pack is composed of a Rotor (turned by the Input Shaft) that is spun inside an eccentric Outer Housing. Eight spring-loaded Slippers move and pressurize the fluid in the Cam Pack before routing it to the Pressure Housing.
RESERVOIR
PRESSURE
HOUSING
FRONT
HOUSING
PULLEY
PRESSURE
VALVE
MOUNTING
STUD
PRESSURE
FITTING
INPUT
SHAFT
TYPICAL
FORD/THOMPSON
PUMP
ROTOR
OUTER
HOUSING
Exploded View - Ford Pump
COMMON PROBLEMS
The most common problems associated with a Ford/Thompson pump is noise, leakage and poor performance (low pressure). These problems are all caused by one or more of the following:
Noise
Many things can cause the pump to make noise. A pump will normally make some noise while operating under certain circumstances. When turning the steering wheel, the pump is called upon to make pressure and will often make some extra noise while doing so. If excessive pressure is being made, or if the wheels are turned to full lock, the Pressure Valve inside the pump will bleed off the excessive pressure, making a producing a notable noise increase in the process.
Air in the system will cause the pump to make noise. Installing a new pump or component, or over-filling the Reservoir, can cause aeration of the fluid, producing a foam of air bubbles. Usually after the system has run a while the bubbles will break down and the noise will subside.
If the system has been run low on fluid, the internal parts of the Cam Pack will lack for lubrication and begin to gall and wear excessively. This will cause the Cam Pack to emit a whine or howl which will not go away even when proper fluid levels are restored.
Leakage
Fluid will leak past the front seal where the Input Shaft goes. This is usually due to the seal becoming hard and brittle from age and heat, causing it not to conform to the shaft surface. Often the seal will get so hard that it will wear a groove into the surface of the Input Shaft. Pumps exposed to water and left to sit will have water seep into the area where the seal sets on the shaft, causing the shaft to rust and pit.
The Reservoir pushes onto the Front Housing and is sealed to it by a large rubber O'ring around its diameter. This rubber O'ring will get hard from age and heat, preventing it from sealings well the the can. Any distortion of the roundness of the Reservoir can cause fluid to leak past an old O'ring. Moisture can accumulate around the lip of the Reservoir where it slides on the Front Housing, causing the can to rust and damage the sealing surface.
Where the Pressure Fitting goes through the back of the Reservoir, there is a paper/fiber washer between the can and the Pressure Housing. Tightening down the nut on the Pressure Fitting clamps the washer between the can and housing which seals it. On pumps with a Mounting Stud coming out of the back of the pump, there is a copper washer inside to the same purpose. If the nuts on either the stud or fitting become loose, fluid from inside the Reservoir will seep past them and cause a leak.
Occasionally the Return Nipple on the Reservoir will be bent or flexed excessively, causing the solder joint where it fastens to the Reservoir to weaken and crack, causing a leak.
Poor Performance (Low Presssure)
A reduction in the strength of the power assist may be noticed, particularly when turning the car at an idle or low speed. Upon raising the speed of the engine, the power to the assist is restored. This is caused by a weak pump that no longer provides the pressure needed to turn the car at low engine speeds.
Usually a pump that has low pressure at low speed has a worn out or damaged Cam Pack. A Cam Pack will not produce sufficient pressure  1) has excessive internal clearances due to wear, 2) has pressure blowby due to damage from being run low on fluid, 3) has weakened or collapsed slipper springs due to high internal temperatures.

Sometimes the valve inside the Pressure Valve will stick due to varnish or contamination, causing pressure to be bled off of the system all the time.
For pictures and more information damage that can be found on a Ford Pump, go to the Can I Rebuild It Myself? page