1.2 Manual Steering Gears

Manual Steering Gears

Manual steering gears convert the rotary movement of the steering wheel into the lateral movement needed to steer the wheels. The two most common types are the recirculating ball steering gear and the rack-and-pinion steering gear. Understanding their components and adjustment procedures is essential for diagnosing steering play, binding, and noise.

Recirculating Ball Steering Gear Components and Operation

The recirculating ball steering gear uses rolling steel balls to reduce friction between the steering shaft and the sector shaft.

• Worm Shaft: The steering shaft connects to the worm shaft inside the gear housing. The worm shaft has a spiral, helical groove cut into its outer surface.
• Ball Nut: A nut with matching helical grooves on its inner surface sits over the worm shaft.
• Recirculating Balls and Guides: Steel balls fill the grooves between the worm shaft and the ball nut. As the worm shaft rotates, the balls roll through the grooves, forcing the ball nut to slide along the worm shaft. Guide tubes route the balls from the end of the groove back to the start, creating a continuous loop.
• Sector Shaft and Pitman Arm: The sector shaft is the output shaft of the gear. It has gear teeth cut into its face that mesh with teeth on the outside of the ball nut. The sector shaft is splined to the pitman arm, which connects to the steering linkage.

Steering Gear Adjustments (Worm Bearing Preload & Sector Shaft Backlash)

If a recirculating ball gear develops excessive play, it must be adjusted in a specific order: Worm Bearing Preload first, and Sector Shaft Backlash second.

• Worm Bearing Preload Adjustment: This adjustment sets the tension on the worm shaft thrust bearings.
  1. Disconnect the pitman arm from the steering linkage to eliminate external resistance.
  2. Back off the sector shaft adjusting screw by turning it counterclockwise two to three turns to ensure there is no interference from the sector shaft teeth.
  3. Attach a dial-indicating inch-pound torque wrench to the steering gear input shaft.
  4. Turn the input shaft and read the rotating torque.
  5. If the torque is not within specification (typically 4–10 in-lb or 0.5–1.1 Nm), loosen the locknut on the worm shaft adjuster plug.
  6. Turn the adjuster plug clockwise to increase preload (tighten) or counterclockwise to decrease it.
  7. Tighten the locknut to specification.
• Sector Shaft Backlash (Over-Center) Adjustment: Backlash is the clearance between the teeth of the sector shaft and the ball nut.
  1. Find the mechanical center of the steering gear by turning the input shaft lock-to-lock, counting the turns, and turning it back exactly half the number of turns. Recirculating ball gears have a "high point" cut into the center teeth, meaning the gears mesh tightest when the steering is centered.
  2. Measure the rotating torque of the input shaft as it passes through the center position (over-center).
  3. The over-center torque should exceed the worm bearing preload by a specific amount (typically an additional 4–10 in-lb, for a total combined reading of 12–20 in-lb or 1.4–2.3 Nm).
  4. If the reading is incorrect, loosen the locknut on the sector shaft adjusting screw located on the gear cover.
  5. Turn the screw clockwise to decrease backlash (increase drag) or counterclockwise to increase backlash.
  6. Hold the adjusting screw and tighten the locknut. Recheck the torque.

Steering Gear Specifications Comparison

Rack-and-Pinion Steering Gear Components and Operation

The rack-and-pinion steering gear is simpler, lighter, and more direct than a recirculating ball gear.

• Pinion Gear: A helical gear connected to the steering column.
• Rack Shaft: A metal bar with gear teeth cut into it. The pinion gear meshes with the rack shaft.
• Rack Guide (Yoke): A spring-loaded metal or plastic plunger that presses against the back of the rack shaft, holding it firmly against the pinion gear to prevent backlash and rattle.
• Inner Tie Rods (Socket Joints): Connect to the ends of the rack shaft and allow the tie rods to move up and down with the suspension.
• Bellows Boots: Rubber boots that cover the inner tie rods and the ends of the rack housing, preventing dirt, road grit, and moisture from contaminating the gear.
• Mounting Bushings: Rubber or polyurethane bushings that bolt the rack housing to the subframe.

Rack Guide Preload Adjustment

If the rack guide wears, the rack shaft will move away from the pinion gear, causing steering play and clunking.

• Adjustment Procedure:
  1. Set the front wheels to the straight-ahead position.
  2. Locate the rack guide adjuster plug on the steering gear housing.
  3. Loosen the locknut on the adjuster plug.
  4. Tighten the adjuster plug to the specified torque (typically 50–70 in-lb or 5.6–7.9 Nm) to seat the guide yoke against the rack.
  5. Back off the adjuster plug by a specific number of degrees (typically 40 to 60 degrees) to establish the correct running clearance.
  6. Hold the adjuster plug and tighten the locknut.
  7. Turn the steering wheel lock-to-lock to check for binding. If the steering is too stiff or fails to return to center after a turn, the preload is too tight.

Troubleshooting Common Steering Gear Symptoms

Technicians must diagnose steering gear wear by identifying specific symptoms:

• Play and Slop: Free play in the steering wheel before the road wheels turn. In recirculating ball gears, this is caused by worn worm shaft bearings or excessive sector shaft backlash. In rack-and-pinion gears, it is caused by a worn rack guide yoke, worn inner tie rod sockets, or worn mounting bushings.
• Steering Binding: Stiff spots or hard steering can be caused by over-tightened adjustments (preload), a bent rack shaft, or damaged gear teeth.
• Noises: A rattling or clunking noise when driving over bumps suggests a loose rack guide yoke, worn steering gear mounting bushings, or worn sector shaft bushings.
• Torn Bellows Boots: Tearing allows water and road dirt to enter the steering rack. This causes rust on the rack shaft, which destroys the inner tie rod joints and the internal rack bushings.