By 1951, many American vehicles required power steering. Gemmer's Hydraguide system, the first power steering system used on an American car, was Chrysler's answer to the massive front end weight created by the new hemi V-8. Other manufacturers quickly followed.

Two power steering designs emerged. Linkage assist steering and the integral power steering gear-each use a constant flow, positive displacement hydraulic pump. The pump, belt-driven by the engine, pressurizes and circulates power steering fluid.

Linkage assist steering consists of a hydraulic control valve attached to one end of the drag link or centerlink. The valve receives input signals from the steering wheel and steering gear. Left or right steering causes the valve to react, opening ports to move hydraulic fluid into a hydraulic ram. The ram attaches to the steering linkage. Fluid directed to one side of the ram's piston or the other determines which direction the power assist will apply.

The linkage assist system is the easiest to adapt. Some truck manufacturers made power assist kits available for dealer installation. The kits worked with the existing manual steer gear and included a drag link and control valve assembly, the hydraulic power ram, a power steering pump with brackets, and the pressure and return hoses.

Linkage power steering makes use of the manual steering gear. On a beam axle model, the control valve attaches to the drag link. The power cylinder's ram end attaches to the tie rod. An anchor bracket supports the cylinder end. For independent front suspension like the '60-66 GM trucks, the control valve attaches to the centerlink at the pitman arm end. Apply pressure is controlled by the valve settings and pump input pressure.

The significant downside to linkage power steering is its vulnerability to damage. The power ram and hoses are continually exposed to the elements, road obstacles and debris.

Integral Power Steering Gears
Modern light trucks use integral power steering. Integral power gears include the control valve, apply piston, and gear system. The assembly mounts to the frame at the same location as a manual steering gear. A pitman arm delivers power from the gear to the steering linkage in the same manner as a manual steering gear.

Light truck power steering came directly from automotive applications. The earliest integral automotive designs were contraptions, a complex melding of manual gear technology and power pistons. Fortunately, Gemmer's Hydraguide and Saginaw's offset applications never made the light truck option list. These designs were cumbersome, taxed horsepower and ate up engine bay space-undesirable traits for a ladder-frame truck.

GM's Saginaw Division eventually developed the most reliable, widely used integral power steering gear in the industry. Rotary valve steering first appeared in 1959 Cadillac, Pontiac, Buick, and Oldsmobile cars. By the late 1960s, all passenger cars and the Chevrolet and GMC light trucks used this gear. Saginaw's rotary valve gears found their way into Ford, Dodge, I-H, and Jeep trucks. Some features of the gear could also be seen in Ford's torsion bar and Chrysler's constant control integral power steering.

The predecessor to rotary valve integral power steering was Saginaw's inline design. Standard for Cadillac and optioned on Buick, Pontiac, and Oldsmobile passenger cars in 1956, the inline gear introduced several innovative features. Unlike the Saginaw offset design, the inline gear could be fitted within a tighter engine bay or into a light truck chassis.