Injector Pump Leak and Repair Strategy on the Case 580SK Backhoe

[MikePhua]

The Case 580SK and Its Fuel System Configuration
The Case 580SK backhoe loader, produced in the early 1990s, was part of Case Corporation’s highly successful 580 series. Known for its mechanical simplicity and rugged performance, the 580SK featured a naturally aspirated diesel engine paired with either a Bosch VE or CAV DPA rotary injection pump, depending on production year and engine variant. These pumps are responsible for metering and delivering fuel under high pressure to each cylinder, synchronized with engine timing.
With tens of thousands of units sold across North America and overseas, the 580SK remains a staple in utility work, excavation, and agricultural operations. However, as these machines age, fuel system leaks—especially around the throttle shaft—have become a common maintenance concern.
Identifying the Source of Throttle Shaft Leaks
A frequent issue on the 580SK is diesel fuel leaking from the throttle shaft on top of the injection pump. This leak typically occurs due to hardened or worn O-rings around the shaft, or in some cases, due to wear in the aluminum housing itself. The leak may appear minor at first but can lead to fuel loss, contamination, and difficulty maintaining engine RPM.
To identify the pump type:

• Bosch VE pumps have a splined throttle shaft with a press-fit bushing
  
• CAV DPA pumps feature a steel shaft running through an aluminum cover with no bushing
  
• The pump part number (e.g., JR916523) and engine serial prefix help confirm the variant
  

Knowing the pump type is critical before attempting repairs, as the procedures and risks differ significantly.
Risks of Disassembling the Bosch VE Throttle Shaft
On Bosch VE pumps, the throttle shaft is splined and must be reinstalled in the exact orientation to maintain proper timing and fuel delivery. Removing the shaft without precise indexing can result in erratic engine behavior or complete failure to start. Additionally, the bushing that supports the shaft is press-fit and requires specialized tools to remove and replace.
Recommendations for Bosch VE:

• Avoid removing the shaft unless equipped with proper jigs and alignment tools
  
• Consider sending the pump to a certified rebuilder for bushing replacement
  
• If attempting a DIY fix, mark the shaft orientation carefully and use a seal kit with OEM-grade components
  

A master rebuilder in South Carolina noted that many DIY attempts on VE pumps result in misalignment and costly damage, advising owners to remove the pump and have it serviced professionally.
Repairing the CAV DPA Pump Shaft Seals
The CAV DPA pump is more forgiving for field repairs. The throttle and shutoff shafts are sealed with O-rings that can be replaced without removing the pump from the engine. The top cover is held on by two acorn-style nuts and can be removed with basic hand tools.
Steps for CAV DPA repair:

• Remove the top cover carefully, noting spring positions and linkage holes
  
• Replace the hardened O-rings with new seals from a mini repair kit
  
• Reuse the gasket if undamaged, or replace with a new one
  
• Reinstall the cover, ensuring springs are placed in correct holes
  

Seal kits are widely available online for under $10 and typically include all necessary O-rings. However, attention to detail is essential—misplacing a spring or linkage can affect throttle response and shutoff behavior.
Impact of ULSD on Older Pumps
The transition to Ultra Low Sulfur Diesel (ULSD) has contributed to increased seal failures in older injection pumps. The reduced lubricity of ULSD causes O-rings to harden and shrink, leading to leaks. Many pumps that were leak-free under high-sulfur diesel now require resealing.
Preventive measures:

• Use fuel additives to restore lubricity and protect seals
  
• Inspect pump seals annually, especially in high-hour machines
  
• Replace O-rings proactively during other fuel system maintenance
  

A technician in Wisconsin noted that nearly every CAV pump he serviced post-ULSD conversion showed signs of seal degradation, even on low-hour machines.
Recommendations for Owners and Mechanics
To address throttle shaft leaks on the Case 580SK:

• Identify the pump type before disassembly
  
• For Bosch VE, avoid shaft removal unless professionally equipped
  
• For CAV DPA, replace O-rings using a mini seal kit and note spring positions
  
• Monitor for leaks after switching to ULSD and consider fuel additives
  
• Keep a parts manual and pump diagram on hand during repairs
  
• Document all repairs and seal replacements for future reference
  

For long-term reliability, consider having the pump professionally rebuilt every 3,000–4,000 hours, especially if operating in dusty or high-load environments.
Conclusion
Throttle shaft leaks on the Case 580SK’s injector pump are a manageable issue when approached with the right knowledge and tools. While Bosch VE pumps demand precision and caution, CAV DPA units offer a more accessible repair path for experienced mechanics. With proper seal replacement, attention to pump type, and awareness of ULSD effects, operators can restore fuel system integrity and keep their 580SK running strong for years to come.