Replacing U-Joints and Input Shaft Seal on a Thomas Protough 1700

[MikePhua]

Thomas Protough 1700 and Its Mechanical Layout
The Thomas Protough 1700 skid steer was part of a compact equipment line developed in the 1990s by Thomas Equipment, a Canadian manufacturer known for rugged, mechanically simple machines. The 1700 model featured a hydrostatic drive system powered by Eaton hydraulic pumps, a chain-driven axle system, and a direct mechanical linkage between the engine and the hydraulic motor via universal joints (U-joints). Though Thomas Equipment ceased operations in many regions, their machines remain in use due to their rebuild-friendly design and durable components.
Diagnosing Input Shaft Seal Leakage
A common issue with aging Protough 1700 units is leakage from the input shaft seal on the hydrostatic motor. This seal prevents hydraulic fluid from escaping where the motor shaft enters the pump housing. Over time, wear from vibration, misalignment, or hardened rubber can cause the seal to fail. Symptoms include visible oil seepage, reduced hydraulic pressure, and contamination around the motor base.
Before replacing the seal, it’s essential to inspect the U-joints for play or binding. Worn U-joints can transmit uneven torque to the shaft, accelerating seal wear. If the seal is replaced without addressing U-joint damage, the problem will likely recur.
Inspecting and Removing U-Joints
U-joints in skid steers are typically cross-type joints with needle bearings housed in bearing cups. To inspect them:

• Check for rotational play by twisting the shaft manually.
  
• Look for rust trails or metal dust around the yoke.
  
• Rotate the joint through its full range to detect binding.
  

If replacement is needed, the joint must be pressed out. A common mistake is applying force across both bearing cups simultaneously in a vise, which can bend the yoke. Instead:

• Position the yoke horizontally in the vise with each tab resting on a jaw.
  
• Use a socket and hammer to drive one bearing cup out vertically.
  
• Repeat for the opposite side.
  

This method isolates force and prevents damage to the yoke. If the joint is seized, grinding or torching the cross may be necessary, but this should be a last resort due to heat distortion risks.
Identifying Replacement Parts
Thomas often used Eaton pumps with custom specifications, making part identification difficult. Many Eaton pumps lack external model tags, especially on OEM-specified units. To identify the correct seal and U-joint:

• Measure the shaft diameter and seal bore.
  
• Record the U-joint dimensions: cross width, bearing cup diameter, and yoke spacing.
  
• Look for stamped part numbers on the pump body or yoke arms.
  

NEAPCO-brand U-joints are commonly used in compact equipment. These can be sourced through industrial suppliers or cross-referenced using dimension charts. Replacement kits typically include:

• Cross shaft
  
• Four bearing cups
  
• Needle bearings
  
• C-clips or snap rings
  

Understanding Premature Wear
In one case, a Protough 1700 with under 900 hours showed significant grooving on six of eight cross legs, despite adequate grease and intact seals. This suggests:

• Misalignment between engine and pump
  
• Overloading during operation
  
• Use of low-quality grease or contamination
  
• Manufacturing defects in the bearing cups
  

To prevent recurrence, ensure proper alignment during reassembly and use high-pressure molybdenum-based grease. Periodic lubrication and inspection every 250 hours can extend joint life.
Replacing the Input Shaft Seal
Once the U-joints are removed, the input shaft seal can be accessed. Steps include:

• Clean the area thoroughly to prevent debris ingress.
  
• Use a seal puller or hooked tool to extract the old seal.
  
• Inspect the shaft for scoring or pitting.
  
• Lightly grease the new seal and press it evenly into place.
  

If the shaft shows wear, consider installing a speed sleeve—a thin metal ring that restores sealing surface without replacing the shaft.
Conclusion
Maintaining the Thomas Protough 1700’s drivetrain requires attention to both mechanical and hydraulic components. U-joint wear and input shaft seal failure are interlinked issues that demand precise inspection and careful replacement. With proper tools, accurate measurements, and quality parts, these repairs can restore performance and prevent future downtime. Despite the brand’s limited support today, the Protough 1700 remains a serviceable and reliable machine for operators willing to engage in hands-on maintenance.