While Chevrolet opted for less expensive linkage power steering on its '55-64 passenger cars and light truck models, GMC Division took a bold initiative that reflected its upscale image. Pontiac became GMC's V-8 engine source for '55-59 pickups. Since Pontiac cars used the inline gear, the GMC V-8s could be readily fitted with a power steering pump. Late '50s GMC 100-300 series models added inline power steering to the option list and became the first trucks to offer integral power steering.

Power Steering Service
Wear and fatigue points on linkage assist steering include the hoses, hydraulic ram cylinder, the control valve, and the power pump. Drivebelt adjustment and replacement are routine service requirements for any power steering system.

The manual steering gear on a linkage power steering system seldom wears. It receives far less load, since the linkage moves under hydraulic pressure. Minor adjustment might be necessary at higher mileage, but unless the hydraulic assist is defective, load wear should be minimal. Fluid levels for the pump and manual gear require periodic checks and topping off. Use gear lube in the manual steering gear and recommended ATF or power steering fluid in the power pump.

Saginaw's 700, 708, 800, and 808 integral gears are extremely rugged. Chrysler constant control and Ford torsion bar integral gears also hold up well. Weaker designs would be the Saginaw 605, which is prone to failure at higher mileage. Due to its compact size, the 605 has been a popular retrofit on street rods and some vintage trucks. The 605 integral-type steering gear does not match the stamina of larger rotary valve designs.

The 700- and 800-series gears have a 70mm piston bore. The 708 and 808 gears benefit from an 80mm bore. The 605 uses a 66.6mm piston, and it does not use a four-bolt cover plate at the adjuster end. Instead, the adjuster/cover plate is a thick cup washer retained by a snap ring. The 605 suits light-duty vehicles like the original S-trucks and some passenger cars. There is a contemporary Saginaw 600-series gear with a 70mm bore and the model 608 gear with an 80mm bore. The modern 600 series has stamina and even NASCAR applications to its credit.

The larger Saginaw rotary valve gears require little attention. The pump will likely fail long before a gear shows wear. Pitman/sector or worm bearing adjustment is seldom necessary between rebuilds. Slight backlash or worm play can be corrected if necessary. Significant worm play, over-center backlash, or any roughness indicate the need for rebuilding.

Hoses are a wear point. On integral systems, there is less movement of hoses, and they are protected within the engine bay. Linkage assist hoses spend a lifetime stretching and flexing as the ram and steering linkage move back and forth. Inspect hoses for nicks, abrasion, deterioration and oil damage. Pressure in the hydraulic system is high, and heat contributes to hose failure. If a fatigued hose sloughs rubber internally, the debris can damage sensitive valves within the power gear and pump.

Service Cautions
A power steering system is much like an automatic transmission. Passageways and valves are close-tolerance and subject to clogging and scoring. Prevent debris from entering the system. Use the recommended fluid. On an older truck that has set up for a long period, flush the system with fresh fluid.

When performing fluid checks or working on the power steering system, protect the pump, hoses and gear assembly from debris. Use the recommended fluid, often Type A or its modern Dexron/Mercon equivalent. If leaks develop at the steering gear or linkage, do not allow the system to run dry. Inspect the pump, hoses and gear seals for signs of seepage.

Rebuilding a pump, control valve, or integral power gear is a responsible job. Before attempting this work, consult the factory shop manual. Be certain you have the right tools and experience for performing work on the steering system.