Steering Box Leaks on IH 4700 Trucks Often Trace Back to Seal Misuse and Pressure Surges

[MikePhua]

The IH 4700 and Its Steering Gear Design
The International Harvester 4700 series, produced through the 1990s, was a popular medium-duty truck platform used for vocational applications ranging from delivery to utility work. These trucks often came equipped with Sheppard-brand steering gears, known for their robust recirculating ball design and integrated hydraulic assist. The steering box itself consists of a control valve housing, piston rack, and input shaft, with hydraulic lines feeding pressurized fluid to assist steering under load.
In high-load conditions—such as when the front axle bears over 10,000 lbs with a tag axle down—steering effort increases dramatically. This puts additional stress on seals and internal components, especially if the system is not properly maintained or pressure relief settings are incorrect.
Common Leak Points and Misdiagnosed Repairs
Leaks typically occur at the junction between the control valve housing and the main gear body, where four bolts secure the assembly. Inside this interface are specialized seals:

• Nylon quad rings
  
• Tetra seals with backers
  
• Square-profile rings designed for high-pressure hydraulic use
  

A frequent mistake is replacing these with standard O-rings, which lack the structural integrity and sealing geometry required for dynamic hydraulic interfaces. O-rings may twist, nick, or deform under pressure, leading to persistent leaks even after reassembly.
One technician discovered that a previous repair had substituted all original seals with generic O-rings. Despite careful installation, the leak persisted until the correct OEM-style seal kit was installed. The proper seals seated easily and resolved the issue in under 15 minutes.
Seal Installation Techniques and Precautions
Installing nylon quad rings and tetra seals requires:

• Warming the seals to soften and expand them
  
• Using a ring compressor to seat them while still warm
  
• Ensuring no twisting or misalignment during insertion
  
• Cleaning all mating surfaces thoroughly to prevent contamination
  

Attempting to install these seals cold or without compression tools often results in poor sealing and premature failure.
Steering Pressure and System Diagnostics
Steering difficulty under load may also stem from incorrect hydraulic pressure. The relief valve is typically located on the pump, not the gear itself. To measure system pressure:

• Install a T-fitting and gauge on the pressure line
  
• Check pressure at idle and under steering load
  
• Compare readings to manufacturer specifications (often 1,500–2,000 psi)
  

If pressure is low, the pump may be worn or the relief valve may be stuck open. High pressure surges can damage seals and cause leaks, especially in older gear housings.
Lessons from the Field
A fleet operator in Mississippi reported steering stiffness and fluid leaks on a heavily loaded IH 4700. After replacing seals with incorrect profiles, the leak worsened. Upon sourcing the correct Sheppard seal kit, the repair was completed quickly and the steering returned to normal. The operator also installed a pressure gauge to monitor future surges.
Another mechanic noted that older steering shafts with plasti-coat splines can peel and jam inside the gear, causing erratic steering and internal damage. Ensuring smooth shaft engagement is critical during reassembly.
Conclusion
Steering box leaks on IH 4700 trucks are often caused by improper seal replacement and hydraulic pressure issues. Using OEM-style seals—such as nylon quad rings and tetra seals—is essential for reliable performance. Technicians should avoid generic O-rings and always verify system pressure to prevent future failures. With proper parts and technique, these steering gears can deliver years of dependable service even under heavy load conditions.