Chapter 46 Steering Systems

Manual Steering Systems Steering system is composed of three major subsystems: Steering linkage Steering gear Steering column and wheel

Steering Linkage Applies to the pivots and connecting parts between the steering gear and steering arms. Transfers motion from the steering gear. The type of front suspension greatly determines the type of linkage.

Parallelogram Steering Linkage Once the most common type. Used with the recirculating ball gearbox. Can be placed in front or behind the front suspension. Provides good steering geometry. Road vibrations and impact forces cause wear and looseness.

Parallelogram Steering

Rack-and-Pinion Steering Linkage Lighter and has fewer components than the parallelogram linkage. The rack performs as steering gear and center link. Tie-rods are the only linkage used. Provides better road feeling but can transmit more road shock.

Rack-and-Pinion Steering System

Manual-Steering Gear Changes rotational motion of steering wheel into a reciprocating motion to move the wheels. Three types currently in use: Recirculating ball Worm and roller Rack and pinion

Recirculating Ball Found in larger cars, trucks and vans. The ball nut moves the worm gear which moves the sector shaft.

Steering Wheel and Column Provides the force to turn the steering gear. Since 1968, all columns are collapsible. Houses the driver side air bag. May have tilt and/or telescoping features. Houses many of the driver operated switches and sometimes the transmission shifter.

Steering Damper Reduces road shock up through the steering column. Found mostly on 4WD vehicles.

Power Steering Systems Reduce driver effort. Major types: Conventional Hydraulic pressure is used to assist the driver Nonconventional Electric motors are used

Power Steering System Types

Integral Piston System Most common power steering system. Uses a pump, reservoir, hoses, and steering gear.

Power-Assisted Rack and Pinion

Power Steering Pump Types Roller Vane Slipper Gear

Flow Control and Pressure Relief Valves Necessary due to engine speed variations. At higher speeds the pump can deliver more flow than is needed.

Power Steering Gearbox Nearly the same as a manual gearbox. Rack and pinion: A rotary valve changes fluid flow Integral piston power steering: A spool valve and power piston are used The spool valve directs oil to the left or right power chamber The spool valve operates by a small torsion bar

Power Steering Hoses Transmit fluid from the pump to the gearbox and back to the pump. Must handle pressures up to 1500 psi. Subject to pressure and pulsations from the pump. Must be able to withstand temperatures of up to 300ºF (150ºC).

Electronically Controlled Power-Steering Systems EPS systems provide increased assist at low speeds and decreased assist at higher speeds. The amount of fluid flow is controlled by a pressure control valve. Uses input from VSS.

Common Steering System Complaints Excessive play Feedback Hard steering Nibble or slight shimmy Pulling or drifting Shimmy Poor return Wandering

Visual Inspection Check the tires first: Power steering drive belt Pressure, size, construction, wear, damage, defects, runout, and balance Power steering drive belt Power steering fluid Fluid leaks

Power Steering Leak Points

Power Steering Fluid Can be checked hot or cold. Most reservoir caps have a dipstick. Some manufacturers recommend specific power steering fluids. Some recommend a type of ATF. Check color, odor, and for signs of metal content.

Pitman Arm Most heavily stressed point in the system. Check for looseness. Removal requires a pitman arm puller.

Idler Arm A worn or damaged idler arm can cause steering instability, uneven tire wear, front-end shimmy, hard steering, and excessive play.

Center Link A worn or damaged center link can cause front-end shimmy, pull, changes in toe, and tire wear.

Tie-Rod Assembly Worn tie-rods result in incorrect toe, scalloped and scuffed tires, wheel shimmy, understeering, noise, and tire squeal on turns.

Dry Park Check Performed with full weight on the wheels. Have an assistant rock the steering wheel back and forth. Check for looseness in the idler arm, center link, tie rods, and pitman arm.

Turning Effort Use a pull scale to read the actual force necessary to turn the wheel. Compare to specifications. Inspect entire steering system if excessive before performing a pressure test.

Rack and Pinion Steering Has only four wear points - the tie-rod ends. Check power units for power steering fluid leaks. Inspect mountings, tie rods, bellows, steering couplings, and gearbox adjustment.

Steering Gear Adjustments Carefully inspect steering and suspension components, wheel alignment, wheel balance, and tire pressure. Wormshaft preload and sector gear preload may be adjustable.

Steering Column Most services are performed with the column installed in the vehicle. Closely inspect the energy absorbing sections of the column. Inspect couplers and steering shaft .

Steering Wheel Place front wheels straight ahead. Disconnect battery negative cable. Remove steering pad and retaining nut. Place alignment marks on shaft and wheel. Disconnect electrical connectors. Use correct puller and remove wheel.

Bleeding the System Performed after replacing any system hydraulic part. Follow service manual procedures. A vacuum pump can be used to purge air. Often running the engine and turning the steering from stop to stop will remove the air.

Hoses and Lines Inspect for leaks, dents, sharp bends, cracks, and swelling. Use exact replacements. Do not attempt to patch or repair. Ensure lines and hoses do not rub against other components.

Power Steering Pump Pulleys may be replaced if bent, cracked, or worn. Some require special pullers and installation tools. Flow control valves and pressure relief valves may be replaceable.

Four-Wheel Steering Systems Mechanical 4WS A steel shaft connects the two gearboxes Hydraulic 4WS Rear wheels turn in same direction as the front Electro/hydraulic 4WS Rear wheels can turn with or opposite front Uses computer monitoring and control

Air Bag Safety Precautions Always wear safety glasses. Follow the manufacturer’s procedure for disarming the system before servicing. Never probe the connectors on the air bag module. Always carry an air bag module with the trim facing away from your body.

Air Bag Safety Precautions (Cont’d) Never set a live air bag module down with the trim cover facing down. Wash your hands with soap and water after working around a deployed air bag.