Where to Find Transmission Parts for the Dresser 520B

[MikePhua]

The Dresser 520B and Its Transmission Origins
The Dresser 520B wheel loader was part of a lineage of mid-sized loaders produced during the 1980s and early 1990s under the Dresser brand, which emerged from the merger of International Harvester’s construction division and Komatsu’s U.S. operations. Dresser Industries, originally a petroleum equipment company, expanded into heavy machinery and became known for durable, straightforward designs. The 520B was widely used in municipal fleets, quarries, and small contractors due to its balance of power and maneuverability.
Unlike many loaders of its class that used ZF or Clark transmissions, the 520B was equipped with a Japan-made transmission, specifically the Model S720, part number 12672751191-520, with serial number OKH CAA9011089. This transmission was likely sourced from a Japanese OEM such as Komatsu or possibly a subcontractor like KAWASAKI Heavy Industries, known for producing industrial drivetrains.
Transmission Characteristics and Terminology
The S720 transmission is a powershift type, meaning it allows gear changes under load without clutch disengagement. This is achieved through planetary gear sets and hydraulic clutch packs, which are actuated by solenoids or mechanical valves depending on the variant.
Key components include:

• Torque converter: Multiplies engine torque and allows smooth starts.
  
• Clutch packs: Engage specific gear sets for forward and reverse motion.
  
• Valve body: Directs hydraulic flow to control gear selection.
  
• Transmission control unit (TCU): In later models, this electronic module manages shift timing and pressure.
  

Understanding these parts is crucial when sourcing replacements, as compatibility depends on internal configuration and control logic.
Sourcing Transmission Parts and Solutions
Finding parts for the S720 transmission can be challenging due to its non-ZF origin and limited documentation. However, several strategies have proven effective:

• Identify the transmission plate: Always begin by locating and photographing the ID plate, which includes model, part number, and serial number. This ensures accurate cross-referencing.
  
• Search by part number: Use the full part number (e.g., 12672751191-520) when contacting suppliers or searching online databases.
  
• Contact Komatsu legacy parts dealers: Since Dresser partnered with Komatsu, some components may be interchangeable or traceable through Komatsu’s parts system.
  
• Explore Japanese industrial transmission suppliers: Companies like KAWASAKI, Hitachi, and Toyo may have produced similar units. Japanese surplus dealers often carry rebuild kits and hard parts.
  
• Use rebuild services: Some transmission shops specialize in obsolete or rare industrial drivetrains. They can fabricate seals, clutch discs, and even valve body components.
  

A contractor in South Carolina once rebuilt his 520B transmission using a combination of Komatsu forklift parts and custom-machined clutch plates. He sourced the valve body from a marine transmission supplier and adapted it with minor modifications. The loader returned to service and operated for another 3,000 hours without issue.
Preventive Maintenance and Troubleshooting
To extend the life of the S720 transmission:

• Change fluid every 500 hours, using high-quality hydraulic transmission oil with anti-wear additives.
  
• Inspect clutch pack wear during service intervals. Slipping or delayed engagement often signals worn friction material.
  
• Monitor shift timing. Harsh or delayed shifts may indicate valve body contamination or solenoid failure.
  
• Check torque converter stall speed. A drop in stall RPM can suggest internal leakage or converter wear.
  

In cold climates, preheating the transmission fluid is recommended to prevent sluggish shifts and seal damage. In dusty environments, external filters and breathers should be cleaned regularly to avoid contamination.
Dresser’s Legacy and Market Impact
Dresser Industries sold thousands of 520B units globally, with strong penetration in North America and parts of Southeast Asia. After its merger with Komatsu, the brand was gradually phased out, but the machines remain in service due to their mechanical simplicity and robust construction.
The 520B’s transmission, while less common than ZF or Allison units, reflects a period of experimentation and global sourcing in the heavy equipment industry. Its continued operation today is a testament to the durability of Japanese industrial engineering and the adaptability of field mechanics.
Conclusion
Finding transmission parts for the Dresser 520B requires persistence, technical understanding, and creative sourcing. By leveraging part numbers, exploring Japanese suppliers, and considering rebuild options, owners can keep these reliable machines running for years to come. The S720 transmission may be obscure, but with the right approach, it remains serviceable and effective in modern workloads.