Sourcing Transmission Parts for the Ford 6500 with Clark HR28300

[MikePhua]

The Ford 6500 and Its Industrial Transmission
The Ford 6500 tractor-loader-backhoe was part of Ford’s heavy industrial equipment lineup in the 1970s, designed for municipal, construction, and agricultural use. Unlike its agricultural cousins, the 6500 featured a reinforced frame, loader towers, and a robust transmission system suited for loader and backhoe work. Many units were equipped with the Clark HR28300 transmission, a hydraulically controlled powershift unit known for its torque capacity and modular design.
Clark transmissions were widely used across industrial platforms, including Case, Massey Ferguson, and Michigan loaders. However, sourcing parts for the HR28300 today can be challenging due to discontinued production and limited aftermarket support.
Identifying the Problem and Missing Components
In one case, a Ford 6500 with a Clark HR28300 had undergone partial transmission service, but critical components were missing or damaged:

• A seat in the pressure regulator valve had been left out during prior disassembly
  
• A chipped disc in another valve was discovered, likely affecting hydraulic modulation
  
• The damaged part was traced to D2NN7R149A, which cross-referenced to a wave washer used in Case applications
  

Wave washers are spring-like discs used to preload valve components and maintain hydraulic pressure balance. Without this washer, the transmission may experience erratic shifting, pressure loss, or complete failure to engage gears.
Challenges in Finding Replacement Parts
The Clark HR28300 is no longer supported by OEM channels, and many parts have been superseded or reclassified under different brands. The wave washer in question was particularly difficult to locate, as it was not listed under the original Ford or Clark part numbers. Cross-referencing revealed its use in Case transmissions, but dimensions and tolerances vary by application.
One technician recommended contacting Joseph Industries, a supplier specializing in legacy transmission components. Joseph Industries maintains a catalog of obsolete Clark parts and offers technical support for matching components across brands.
Best Practices for Transmission Rebuilds
When rebuilding or servicing a Clark HR28300:

• Always use a complete valve breakdown diagram to verify component placement
  
• Inspect all valve seats, springs, and washers for wear or omission
  
• Replace seals and gaskets with high-temperature rated materials
  
• Flush the transmission housing to remove debris from previous failures
  
• Use a pressure gauge to test clutch pack engagement and regulator function
  

If parts are unavailable, consider fabricating replacements using OEM specs. A machinist in Pennsylvania successfully replicated a wave washer using spring steel and a lathe, restoring function to a Michigan loader with the same transmission.
Alternative Solutions and Long-Term Strategy
If sourcing parts proves impossible, options include:

• Swapping the transmission with a compatible unit from a salvage machine
  
• Retrofitting a manual gearbox, though this may require frame and linkage modification
  
• Converting to electric clutch control, bypassing hydraulic modulation
  

For fleet operators, maintaining a parts log and sourcing backup components from retired machines can prevent downtime. Joining vintage equipment forums and parts exchanges may yield rare components or fabrication templates.
Conclusion
The Ford 6500’s Clark HR28300 transmission remains serviceable with the right knowledge and sourcing strategy. Missing components like wave washers can cripple hydraulic function, but with careful cross-referencing and support from legacy suppliers, repairs are possible. For owners of vintage industrial tractors, preserving transmission integrity is a blend of mechanical skill, historical research, and creative problem-solving.