Introduction To Power Steering Systems Essay
Introduction To Power Steering Systems
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.This apparatus is a Saginaw… read full captionThis apparatus is a Saginaw offset integral steering gear. Introduced in 1952 GM luxury models, the design preceded Saginaw’s inline gear.
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Like the Gemmer Hydraguide, the offset was essentially a manual steering gear with a parallel power assist cylinder and rack drive. The unit was too large for light truck, ladder frame use.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.Saginaw’s inline integral… read full captionSaginaw’s inline integral steering gear came online in 1956. A compact unit, the inline became a GMC light truck option. Despite use on luxury GM cars and the GMC trucks, there were weaknesses in the design. GM phased out the inline within four years of its introduction. The better inline features carry forth to the rotary valve steering gear.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.Saginaw’s inline introduced… read full captionSaginaw’s inline introduced the recirculating ball nut-and-worm power rack piston. In this design, the ball nut and rack piston are separate pieces. During assembly, the ball nut (shown at right) is secured within the rack piston (left) by a tapered set screw. On the subsequent rotary valve design, the ball nut and rack piston is a single, machined piece.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.Originally staked in place,… read full captionOriginally staked in place, this ball nut screw was eventually welded by Saginaw for safety. Use a genuine Saginaw tapered screw and torque to specification. High-strength TIG welds will prevent the set screw from backing out. Weld crowns must be lower than the diameter of the piston head to prevent interference with the cylinder bore.This GM Saginaw pump was common… read full captionThis GM Saginaw pump was common to offset and inline era applications. Rugged design uses sliding vanes and an oblong pump ring to pressurize fluid.
The fluid reservoir looks sturdy; however, the canister is stamped tin. When adjusting the belt on a GM vane pump of this type, do not pull on the reservoir tank. Its base will distort and leak.Uncomplicated, the vane pump… read full captionUncomplicated, the vane pump has a slotted rotor, vane blades, and an oblong pump ring. A machined pressure plate (removed here) and flow control valve maintain a calibrated pressure and volume flow. Balance springs and a relief valve determine pressure constants. After charging the gear assembly, excess fluid circulates back to the reservoir.This is a Federal slipper-type… read full captionThis is a Federal slipper-type pump, found mostly on Chrysler applications. Dodge and Plymouth trucks use this design with Chrysler’s constant control integral power steering gear. Rebuild kits are available. Following a factory workshop manual, this job can be done at your home shop, using a regular set of tools.
Thompson pumps have simple… read full captionThompson pumps have simple service and overhaul needs. After washing and careful inspection, this pump is rebuildable. At right is the rebuild kit, consisting of O-rings, seals and gaskets. These pumps are common on Ford cars and light trucks of the late ’50s and ’60s. Service parts are available through CLASSIC TRUCKS’advertisers.Ford/Thompson fluid reservoirs… read full captionFord/Thompson fluid reservoirs develop leaks at seams. Brazing is a permanent fix, restoring the strength and function of these stamped sheetmetal parts. Glass beading and a wash will remove the flux and prepare the brass areas for primer and paint. As parts age and become scarce, restoration is the reasonable alternative.Saginaw rotary valve 800 and… read full captionSaginaw rotary valve 800 and 808 steering gears are common to light GM trucks and other applications. Unlike the inline gear, the rack piston and worm outer ball bearing is one piece. During overhaul, balls load into the piston rack, winding their way around the worm shaft. This design distributes loads evenly between the rack piston and worm.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.
New bearings and seals restore… read full captionNew bearings and seals restore an 800 gear. Adjustments follow factory steps. Similar to a manual gear, the two concerns are worm bearing preload and over-center mesh load at the sector teeth. Adjustment begins with the worm bearings. Tool required is an in/lb torque wrench. Final setting (shown) is over-center rack tooth and sector mesh.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.Saginaw 605 gear has become… read full captionSaginaw 605 gear has become popular for tight-space conversions. This gear is lighter duty than the 700- and 800-series designs.
If you select a 605 for your conversion, do not bother with a recycled unit. There is no such thing as a “good used” Saginaw 605. A better bet is a quality rebuild from a reputable source or an 800/808 or 700/708 gear.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.|
Read more: http://www.classictrucks.com/tech/1002clt_introduction_to_power_steering_systems/viewall.html#ixzz2H10OEgWh
University/College: University of California
Type of paper: Thesis/Dissertation Chapter
Date: 10 December 2016