Diagnosing and Repairing Transmission Issues in the Case W20 Loader

[MikePhua]

The Case W20 and Its Place in Loader History
The Case W20 wheel loader was introduced in the late 1970s as part of Case Corporation’s expansion into mid-size earthmoving equipment. Known for its rugged build and straightforward mechanical systems, the W20 was widely adopted in construction, agriculture, and municipal fleets. Case, founded in 1842 and later merged into CNH Industrial, had already built a reputation for durable tractors and backhoes. The W20 series—including variants like the W20B and W20C—sold tens of thousands of units globally, with many still in operation today due to their rebuild-friendly design and parts availability.
The W20 typically came equipped with a 2000 Series TT Allison transmission, offering two forward gears and one reverse. While the transmission was robust, age and wear have made failures increasingly common, especially in machines with high hours or poor maintenance records.
Common Symptoms of Transmission Failure
Operators often report sluggish movement in first gear and complete loss of drive in high gear. These symptoms are usually accompanied by metallic debris in the transmission oil, indicating internal component wear or failure.
Typical signs include:

• Weak or no movement in high gear
  
• Reduced torque in low gear
  
• Steel flecks in drained transmission oil
  
• No improvement after filter replacement
  

Terminology:

• Sprag Clutch: A one-way clutch that allows rotation in one direction and locks in the other, often used in automatic transmissions.
  
• Torque Converter: A fluid coupling that transfers rotating power from the engine to the transmission.
  

In one case, a Nebraska operator found steel particles in the transmission pan and suspected a failed sprag clutch. A mechanic confirmed the diagnosis but warned that further damage could exist, requiring a full teardown.
Sprag Clutch Failure and Its Consequences
Sprag clutch failure is a known issue in older Allison transmissions. When the clutch loses its locking ability, the transmission can no longer engage gears properly. If the machine continues to operate after symptoms appear, additional damage to plates, bearings, and the converter may occur.
Key risks of continued operation:

• Scoring of internal surfaces
  
• Damage to reverse plates and discs
  
• Contamination of hydraulic circuits
  
• Increased labor costs due to deeper teardown
  

Terminology:

• Scoring: Surface damage caused by metal-on-metal contact.
  
• Reverse Plate: A clutch component that engages reverse gear through hydraulic pressure.
  

A Canadian technician recalled a W20 that had been run for weeks with poor drive performance. By the time it reached the shop, the transmission required a full rebuild, including new pistons, seals, and a converter replacement—costing over $6,000 in parts and labor.
Parts Pricing and Rebuild Considerations
Rebuilding a TT 2000 Series transmission is labor-intensive and parts can be expensive. However, sourcing components through Allison dealers rather than Case-branded channels can reduce costs significantly.
Estimated parts pricing:

• Gasket set: $1,200+
  
• Freewheel clutch kit: $945
  
• Charge pump: $1,100
  
• Low range plates (x4): $270 each
  
• High range plates (x3): $175 each
  

Additional components may include:

• Bearings
  
• Reverse discs
  
• Pistons
  
• Torque converter
  

Terminology:

• Charge Pump: A pump that supplies hydraulic pressure to engage clutches and shift gears.
  
• Freewheel Clutch: A clutch that disengages automatically when torque is removed, allowing coasting.
  

A fleet operator in North Carolina reported saving nearly $2,000 by sourcing parts directly from an Allison distributor. He also emphasized the importance of having a service manual specific to the TT transmission, which helped avoid assembly errors.
Preliminary Checks Before Full Teardown
Before committing to a full transmission removal, several diagnostic steps can help rule out external issues. These include checking air lines, clutch cutout valves, and hydraulic pressures.
Recommended checks:

• Clean debris under brake pedals to prevent false clutch disengagement
  
• Disconnect air line to clutch cutout and verify pressure
  
• Remove and clean clutch valve spool and piston
  
• Inspect trimmer circuit in control valve
  
• Bleed air tanks to remove water and oil contamination
  

Terminology:

• Clutch Cutout Valve: A valve that disables clutch engagement when brakes are applied.
  
• Trimmer Circuit: A hydraulic control path that fine-tunes clutch pressure for smooth engagement.
  

In one instance, a technician found that a clogged clutch valve was preventing proper pressure buildup. After cleaning the spool and piston, the transmission regained partial function—buying time for a planned rebuild.
Labor and Downtime Implications
Removing the transmission from a Case W20 requires engine removal and disassembly of the converter housing. This process can take 12–20 hours depending on shop setup and technician experience. Labor costs vary widely, but most shops charge $90–$150 per hour.
Estimated labor breakdown:

• Engine removal: 4–6 hours
  
• Converter disassembly: 2–3 hours
  
• Transmission removal: 3–5 hours
  
• Rebuild and reinstallation: 6–10 hours
  

Terminology:

• Converter Housing: The casing that holds the torque converter and connects to the engine flywheel.
  
• Magnet Inspection: Checking for metal debris on internal magnets to assess wear.
  

A Minnesota mechanic shared that he often finds sprag rollers lodged in the transmission screen during teardown. This is a clear sign of clutch failure and usually justifies a full rebuild.
Conclusion
Transmission problems in the Case W20 loader are often rooted in sprag clutch failure, compounded by age and contamination. While parts are available, costs can escalate quickly without proper diagnosis and sourcing. Preliminary checks may reveal external issues, but once internal damage is confirmed, a professional rebuild is usually necessary. For owners of these legacy machines, understanding the transmission’s mechanics and planning for downtime can make the difference between a costly overhaul and a strategic repair.