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Rebuilding the Ford/Thompson Pump
This section is primarily about the 1965-1978 Ford Thompson (TRW) design power steering pump
Rebuilding a Ford/Thompson-style pump unit is seldom an easy thing to do. Before you consider or attempt a rebuild, there are some problem areas you should be aware of. This first part is not designed to scare you off from attempting your own rebuild (well, maybe just a little), but to show you what you may encounter along the way. I have done many Ford/Thompson pump rebuilds and see these problems on almost a daily basis. These are the things not mentioned in any instruction sheet or shop manual.
Problems You May Encounter ( And not really be aware of )
The Ford Thompson-style pump came out in 1965 as a replacement for the earlier Eaton-style pumps used the previous ten years or so. It offered two major improvements over the earlier design; it used pressurized slippers instead of loose rollers to provide higher hydraulic pressure at lower engine speed, and it used a pump that was fully enclosed and cooled by the fluid reservoir. These improvements did favor the new models cars of the time, but the integral reservoir created some engine compartment clearance problems, and the new slipper design pumping action caused the pump and fluid to run hotter.
Depending on the brand and distributor of the rebuild kit you buy, the included instructions (if any) are likely to be fair to worthless. Even the instructions and illustrations found in factory Ford shop manuals have mistakes and inaccurate information. Sometimes the information given will not even work on the year and model pump the book claims to cover. The most important thing to remember is that typical kit and shop manual instructions were originally designed for mechanics that worked on these pumps during a warranty period or reasonable time span from when the car was new. They do not address the problems and situations that can come up on rebuilding a 25-30 year old pump that may or may not be complete, original or in rebuildable shape.
The most common problems found in the Ford pump are:
Cam Pack wear, which causes the pump to whine when operating
Pressure Valve sticking, which causes sudden loss of pressure and power assist
Slipper Spring tension loss, which causes lower pump pressure and harder steering
Leakage, which is caused by hardened seals and worn sealing surfaces
These problems can all be attributed to two major problems.
First is the pump being run out of or low on fluid. This is usually from an unrepaired leak or from disconnecting the hoses from a leaking system but leaving the belt hooked to the pump. Fluid runs low and the Cam Pack starts to over work and burn up what little fluid is left insdie the pump cavity.
The second problem is when the fluid is over-heated from hot weather and parking lot manuevers or from being worn out and never changed. The fluid then breaks down and fails to lubricate as it should. This also causes the cam pack to wear and cause noise. The fluid begins to turn to varnish and causes the valves in the pressure valve to stick. Metal begins to shed off the internal parts and this too adds to the sticking and wear. The seals get hard from overheating and become so hard that they actually begin to wear grooves in the steel input shaft.
Wear and damage from heat and worn out fluid is what you have to look for in a pump rebuild. The pump is the worker and heat builder of the power steering system and is most affected by the stress and heat. The metal that wears off inside the pump will contaminate the rest of the system and cause problems throughout.
Due to numerous replacements over the years, very few cars still have the correct pump and Reservoir on their car. If your pump needs a rebuild, and you are interested in keeping the car original, then this is the time to look into replacing your pump with a correct unit. If you are not particular about correctness, then you should at least check that the pump will fit and hookup properly for your application.
Is the Pressure Fitting correct style and length for the correct hoses? Does your pump require an internal Mounting Stud to mount correctly? Is the Filler Tube the correct diameter and angle to clear the engine and components? Is the Return Nipple the correct length and pointing in the correct direction for the Return Hose to fit correctly?
Similar to Mustang
The return hose nipple turns upward and location of pressure fitting and mount stud holes are different. Reservoir will not match up with
1965-1966 MUSTANG 289 with Air Conditioning
Correct reservoir with large, tilted neck, angled return nipple and rear hole locations
style cannister but
return nipple is
with correct straught
To seal properly the holes in the back of the Reservoir for the Pressure Fitting and Mounting Stud must be round and burr-free. The Filler Tube and Return Nipple must have no cracks or breaks where it mounts to the can. The inner lip where the Front Housing and O'ring seals must be smooth, round and free of creases, dents or rust pitting.
RUSTED INNER LIP
DAMAGED RESERVOIR HOLES
CRACKED RETURN HOSE NIPPLE
The Input Shaft can be damaged in several ways: 1) surface scored by hardened or dirt-impregnated front seal, 2) scored from damaged Pump Bushing, 3) rust pitted from moisture accumulation around front seal, 4) pulley installation bolt broken off inside shaft.
The surface of the Input Shaft is a hard-chrome plating. Even so, the surface can be damaged beyond use. Any pitting or scoring where the front seal rubs will cause leakage and any damage where the shaft spins in the bushing will only cause more damage. In either case, the Input Shaft must be replaced.
The Input Shaft spins inside an aluminum Bushing mounted in the Front Housing. This Bushing is not pressure lubricated but usually receives enough lubrication to operate properly. If the pump is run evry low on fluid, the shaft and bushing may run dry. This is also possible if the lubrication hole to the backside of the Front Seal becomes blocked with debris. If the Bushing is scored or damaged in any way, it must be replaced. Care must be taken removing the old Bushing and pressing in the new one. Deformation of the Bushing or its outer edges will cause the Input Shaft to bind and score.
SHAFT SCORED BY DAMAGED BUSHING
The Cam Pack is the heart of the pump, providing the pumping action of the fluid and the high pressure needed for the system. Because it has such a large surface area where metal rubs against metal, it requires a constant and clean supply of fluid. Loss of lubricating fluid, even for a short time, will rapidly cause metal-to-metal contact, resulting in severe wear and/or damage. Any particles suspended in the fluid will be forced into the Cam Pack parts as it pressurizes the fluid, causing scoring. Over-heating of the Cam Pack will cause the Slipper Springs to loose tension and collapse and they will no longer seal the Slippers to the Cam Housing. If any of these things happen, the Cam Pack will need to be rebuilt or replaced.
Unfortunately, Cam Pack replacement is not always easy. Ford used two different thicknesses of Cam Packs during production, and they must each be used with Input Shafts, End Plates and Pressure Plates that match. Most classic Fords use the thinner-style Cam Pack which is not currently available. The later model thicker Cam Pack can be installed in its place, but all the matching components must be installed with it or Input Shaft end play will be excessive.
The rotor inside the campack is a critical part. They are often damaged by metal fragments in the fluid and running the pump low on fluid. Any damage to the rotor will cause the pump to whine and howl.
The rotor on the left has been run low on fluid and over-heated. You can see the scuff marks from galling and from high temperatures.
A closeup picture on the right shows a common problem; stress cracks. This rotor is about to break apart and shed metal into the system.