Troubleshoot your power steering problems with our DIGITAL MECHANIC
Whenever steering complaints are encountered it is important that the complete steering system be inspected. Special body or equipment installations should also be considered for their effect on steering performance.
The steering system consists of the Sheppard Integral Power Steering Gear, a hydraulic supply pump with pressure and flow controls and an oil reservoir, the front axle and mechanical components and the steering column or input shaft and connecting linkages. The front tires and wheels must also be consideted as part of the total steering system. Steering performance can be affected by out of line conditions anywhere in the total steering system. Other factors outside the steering system can also contribute to poor steering performance. Many times a steering gear is removed and disassembled needlessly, because an organized diagnostic procedure has not been followed. Start your diagnosis by:
Defining the complaint
talk to the driver
drive the vehicle
Look for poor loading practices
Check tires for mismatch and proper air pressure
Check for dry fifth wheel or improper location
Check suspension for sagging or shifting (out of line rear axles will tend to steer the front end of the vehicle)
Mechanical components inspection
Check all front axle components for wear looseness or seizure
Inspect front and rear suspension components
Check steering gear mounting to be sure it is tight and not shifting on the chassis or axle
Inspect steering column components
Hydraulic Supply system inhection
Evaluate hydraulic supply system performance. Follow procedures in Hydraulic Supply Diagnosis. Oil pressure and oil flow must be within the vehicle manufacturer's specifications.
The following chart lists possible symptoms, causes and corrective action for steering system complaints. Careful and complete diagnosis will enable you to solve steering problems quickly.
Universal joints are designed to operate best when the angle between the drive and driven shafts is a maximum of 20 to 25 degrees. Angles greater than this will cause undesirable velocity changes between the two shafts. This velocity change may upset steering performance. When two universal joints are used, it is in most instances possible to phase the two joints to match a high and low velocity in a manner that will provide equal velocity between the drive and driven shafts. A third universal joint in the shaft arrangement can upset the phasing of the first two joints and it is important that this third joint's operating angle is limited to a maximum of 20-25 degrees.
Phasing of the universal joints in the steering column can be checked quite easily. Using an inch-pound graduated dial reading type torque wrench, read the variation in the torque reading while steering from lock-to-lock, with a socket on the steering shaft nut under the horn button. Variation of more than 15 in. lbs. indicates improper phasing. This reading is taken with the vehicle stationary and the engine running.
Phasing can usually be accomplished by rotating the two piece intermediate shaft on spleen at a time until the torque reading remains he same all the way around the 360 degree rotation of the steering wheel.
Acme thread wear usually comes from inadequate lubrication or excessive manual steering of the vehicle. Manual steering results from inadequate pump pressure or flow, or an overloaded front axle where you need steering forces in excess of the hydraulic design of the steering gear.
Freeplay the movement of the shuttle type actuating valve within the piston, along with the normal clearances required between operating parts in the steering gear will produce a certain amount of unresponsive motion at the rim of the steering wheel. This unresponsive motion is inherent to the design and must be considered normal.
With recent advances in technology and manufacturing methods it has been possible to considerably reduce the amount of unresponsive motion. Steering gears in service prior to July 1978 could be expected to have 3.5 to 4 inches of unresponsive motion. Current production Sheppard steering gears in service will have 1.5 to 2.5 inches of unresponsive motion. Various combinations of steering gear ratios and steering whell diameters could effectively reduce these maximum allowances. Nominal unresponsive motion in Series 6 steering gears, measurable to 0.5 to 1.5 inches.
Unresponsive motion is measured at the rim of the steering wheel. It must, therefore, be noted that any freeplay in the steering column and related components will affect your measurement. The steering gear mounting must be tight and steering linkage wear adjusted out or worn parts replaced.
The vehicle should be standing on a smooth shop floor with the engine idling when unresponsive motion is checked.
Measurement is made at the rim of the steering wheel, from initial tire and wheel movement left steer, to initial tire and wheel movement right steer.
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