Steering Box Adjustment on the Chevrolet C70 Medium-Duty Truck

[MikePhua]

The Chevrolet C70 and Its Role in Commercial Transport
The Chevrolet C70 was part of General Motors’ medium-duty truck lineup during the 1970s through the early 1990s. Built for vocational use—ranging from dump trucks and grain haulers to flatbeds and utility rigs—the C70 offered a balance of payload capacity, durability, and serviceability. With a gross vehicle weight rating (GVWR) typically between 23,000 and 33,000 pounds, it was powered by gasoline or diesel engines mated to manual or automatic transmissions.
The steering system on the C70 was designed for rugged use but often required periodic adjustment due to wear in the steering box, pitman arm, and linkage components. As these trucks aged, steering play and wandering became common complaints, especially in units used for off-road or agricultural work.
Terminology Notes

• Steering Box: A gear-driven mechanism that converts steering wheel rotation into lateral movement of the pitman arm
  
• Pitman Arm: A lever attached to the steering box output shaft that moves the steering linkage
  
• Sector Shaft: The output shaft of the steering box that drives the pitman arm
  
• Worm Gear: The input gear inside the steering box that meshes with the sector shaft
  
• Preload Adjustment: A procedure to reduce internal play by tightening the gear mesh within the box
  

Symptoms of Steering Box Wear
Operators of aging C70 trucks often report:

• Excessive steering wheel play before wheels respond
  
• Vehicle wandering at highway speeds
  
• Difficulty maintaining lane position
  
• Clunking or knocking noises during turns
  
• Uneven tire wear due to misalignment
  

These symptoms typically point to internal wear in the steering box, loose sector shaft bearings, or misadjusted gear mesh. In one case, a grain hauler in Iowa noticed his C70 drifting unpredictably on gravel roads. After inspecting the steering box, he found the sector shaft preload had loosened over time, allowing excessive movement.
Adjustment Procedure and Safety Considerations
Before adjusting the steering box:

• Park the truck on a level surface and chock the wheels
  
• Disconnect the battery to prevent accidental starter engagement
  
• Clean the steering box exterior to avoid debris entering the housing
  
• Inspect the pitman arm and linkage for wear or looseness
  

Adjustment steps:

• Locate the sector shaft adjustment screw on top of the steering box
  
• Loosen the locknut while holding the screw stationary
  
• Turn the screw clockwise in small increments (typically 1/8 turn)
  
• Re-tighten the locknut and test steering wheel play
  
• Repeat if necessary, but avoid over-tightening which can cause binding
  

If the steering becomes stiff or does not return to center after a turn, the adjustment may be too tight. Back off slightly and retest. Always check for full range of motion and smooth operation before returning the truck to service.
Additional Inspection Points
Beyond the steering box, check:

• Tie rod ends for play or torn boots
  
• Drag link bushings for wear
  
• Steering column universal joints for binding
  
• Frame mounting bolts for torque and integrity
  
• Power steering fluid level and pump output (if equipped)
  

A technician in Georgia once traced erratic steering to a cracked frame bracket that allowed the box to flex under load. After welding and reinforcing the mount, the truck tracked straight even under heavy payload.
Preventive Maintenance Recommendations
To maintain steering performance:

• Inspect steering components every 10,000 miles or quarterly
  
• Lubricate linkage points with high-pressure grease
  
• Replace worn bushings and tie rod ends promptly
  
• Flush power steering fluid every 30,000 miles
  
• Keep tires properly inflated and aligned
  

For trucks operating in off-road or agricultural environments, consider installing steering stabilizers or reinforced pitman arms to reduce stress on the box.
Stories from the Field
A municipal crew in Nebraska used a C70 dump truck for snow removal. After noticing increased steering effort during plowing, they discovered the box preload had backed off due to vibration. A simple adjustment restored control and reduced driver fatigue during long shifts.
In another case, a restoration enthusiast in Texas rebuilt his C70’s steering box using a kit sourced from a vintage parts supplier. After reassembling with new bearings and seals, he reported that the truck handled like new—even with 300,000 miles on the chassis.
Conclusion
Steering box adjustment on the Chevrolet C70 is a straightforward but critical procedure to restore handling and safety. With proper tools, attention to preload settings, and a thorough inspection of related components, even high-mileage trucks can regain precise steering response. Whether hauling gravel, grain, or municipal loads, the C70 remains a dependable workhorse when its steering system is properly maintained.