How It Works - Eaton Pump

The Eaton design pump is a very simple design. It was used throughout the mid to late 1950's on into the 1980's on a variety of vehicles including General Motors, American Motors, Studebaker, tractors and large commercial trucks. Early designs used a rotor and cam ring design similar to that used in modern automotive oil pumps, but by the late 1950's had settled into the common Roller Pump design.
The Pulley driven Input Shaft spins an internal Rotor mounted inside an eccentric-shaped Cam Ring. The rotating action throws the Rollers to the outside of the Rotor and against the inside surface of the Cam Ring. Due to the out-of-round shape of the inside of the Cam Ring, the Rollers alternately pull in, pressurize, and release the fluid. A Pressure Valve with an internal Relief Valve controls the maximum pressure made by the pump and prevents excessive pressure buildup when the cars wheels are turned to full lock.
Some models used a pressure fitting mounted in the Pressure Valve retaining nut to slightly increase engine speed during certain conditions.

On some cars, such as 19XX-19XX Thunderbirds, pressurized fluid from the power steering system was also used to power the windshield wipers. Hoses ran into the cowling at the base of the windshield to a hydraulic motor which operated the wipers.

Excessive Wear
The areas of most common wear is the Rollers and the inside surface of the Cam Ring where they roll. The Rollers have a hard chrome plating that will often wear through and/or flake off once it becomes thin. The Roller will show the underlying metal under the plating and will no longer be smooth and round. The inside surface of the Cam Ring will wear to the point that the Rollers have a difficult time sealing and pressurizing the fluid, resulting in blow-by and low pump pressure at idle.
The round key locating the Rotor on the Input Shaft is a rather loose fit and will often become damaged through normal use, causing the Rotor to be quite loose on the shaft.
Occasionally the surface of the Input Shaft, where it goes through the Front Seal, will have grooves worn into it from the seal.

IInput Shaft Bushing Wear
On the standard-style Eaton Pump, the input shaft runs on two bronze bushings instead of any kind of needle or ball bearing. These bushings are not pressure lubricated, and after many years of service, they wear down and the clearances to the input shaft become sloppy and excessive. When this happens, the input shaft will have so much wobble and side play, that the front shaft seal cannot stretch enough to properly seal against the shaft, and even a new front seal will leak.
These bushings were never sold separately, but only came in new housings, which are also long out of production.

Corrosion
Unless exposed to the weather, water seldom gets into the system of an Eaton pump and there is rarely any corrosion damage inside. The only area prone to corrosion damage is the Input Shaft where the front seal rides. The seal can retain moisture and cause pitting in the hardened surface of the Input Shaft around the area of the seal. This will damage cause damage to the seal surface and leakage, even in a new seal.

Physical Damage
Most physical damage is caused by improper assembly of the pump during a rebuild. The Cam Ring is prevented from rotating inside the Rear Housing by a very small metal pin located at an angle inside the housing. If the Cam Ring is not installed properly, the pin will be damaged and the Cam Ring will not sit properly inside the housing. This will usually cause all of the internal parts to become damaged during use, often including the housings.
The most common damage on the Eaton pump is to the Reservoir mounted to the pump. The return hose nipple is often bent or kinked. Due to the difficulty of reinstalling the top piece of the reservoir, often the holddown bolt or the piece it screws into is damaged.