Dresser 515C Transmission Overheating and Shuttle Shift Failure

[MikePhua]

The History of the Dresser 515C Loader
The Dresser 515C was part of the mid-1980s evolution of industrial loaders developed under the Dresser brand, which emerged after International Harvester’s construction division was acquired and restructured. Dresser Industries, originally focused on oilfield equipment, expanded into earthmoving machinery and continued producing wheel loaders, dozers, and graders. The 515C was designed as a versatile, mid-size loader powered by a Cummins 5.9L diesel engine, paired with a torque converter transmission and shuttle shift system. Though production numbers were modest compared to Caterpillar or Case, the 515C earned a reputation for mechanical simplicity and rugged performance in municipal and agricultural fleets.
Terminology Annotation

• Torque Converter: A fluid coupling that multiplies engine torque and transmits it to the transmission without direct mechanical contact.
  
• Shuttle Shift: A transmission feature allowing quick directional changes between forward and reverse, often used in loading operations.
  
• Charge Pump: A hydraulic pump supplying pressurized oil to the transmission and torque converter.
  
• Hook Ring Seal: A specialized internal seal that directs oil flow within the transmission; failure can cause bypassing and overheating.
  
• Foaming: The presence of air bubbles in hydraulic or transmission fluid, which reduces lubrication and causes erratic pressure behavior.
  

Symptoms of Transmission Trouble
The 515C in question exhibited a recurring issue: after extended operation under moderate to heavy load, the transmission would hesitate or fail to engage reverse. Initially, the transmission fluid overheated during roading in third gear. After replacing coolant and hydraulic fluid, and repairing a leaking hydraulic hose, the issue seemed resolved—until the transmission began overfilling itself with hydraulic fluid. This pointed to internal leakage between systems.
Further investigation revealed a failed seal in the hydraulic pump, allowing hydraulic fluid to migrate into the transmission. After replacing the seal and rear main engine seal, the machine operated normally for light-duty tasks. However, under heavy torque converter load—such as pushing through dense brush—the transmission would again hesitate during shuttle shifts and eventually stop until cooled.
Pressure Behavior and Diagnostic Observations
A pressure gauge installed on the main transmission port showed nominal pressure at 300 psi, with brief drops to 100 psi during shifts. When the transmission failed to shuttle, pressure remained at 100 psi until the shift completed. High-RPM shifts were more successful, but not ideal for long-term reliability. The transmission fluid also showed signs of foaming, with large soda-like bubbles—not the milky appearance typical of water contamination.
This foaming suggested air ingress, possibly between the sump and charge pump. Despite no visible leaks, the pump was removed and tested under vacuum, showing no failure. The issue only occurred under load, not during idle, further pointing to dynamic air intrusion or internal bypassing.
Stall Test and Torque Converter Evaluation
A stall test was performed by placing the loader in third gear, applying full throttle while holding the brakes. The torque converter temperature rose rapidly, confirming active torque multiplication. When shifted to neutral and throttled up, the torque temperature dropped sharply while coolant temperature climbed—indicating proper converter disengagement. This test ruled out complete torque converter failure but suggested internal leakage or inefficient cooling under load.
Possible Causes and Repair Strategies

• Internal steel tube crack between suction screen and pump inlet, allowing air ingress under load.
  
• Hook ring seal failure, causing oil to bypass the cooler and return directly to the drop box.
  
• Improper fluid specification; switching to CAT TO-4 oil worsened foaming, suggesting additive incompatibility.
  
• Misplaced return dumps in the transmission housing, leading to turbulence and aeration.
  

Recommended Actions

• Replace transmission fluid with HyTran or equivalent tractor hydraulic fluid known for anti-foam properties.
  
• Inspect internal suction tubes for cracks using dye penetrant or pressure testing.
  
• Recheck all seals and gaskets between hydraulic and transmission systems.
  
• Monitor transmission temperature and pressure during varied load cycles.
  
• Consider installing an external transmission cooler if operating in high ambient temperatures.
  

Anecdote from the Township Fleet
This particular 515C had a known history of shuttle shift hesitation dating back 15 years when it was operated by a local township. Even then, under heavy gravel loading, the transmission would pause before engaging reverse. After being sold to a private hauler and later retired, the loader was revived for agricultural lime loading. Despite its age and quirks, the machine remained mechanically tight, with minimal pin wear and a surprisingly low hour count—suggesting that the transmission issue was chronic but not catastrophic.
Conclusion
The Dresser 515C’s transmission trouble reflects the challenges of diagnosing fluid dynamics in older torque converter systems. While mechanical components may remain intact, internal seals, fluid compatibility, and air management play critical roles in performance. Foaming, pressure drops, and shuttle hesitation are often symptoms of deeper hydraulic imbalances—not just worn clutch packs or overheating.
For operators and restorers, understanding the interplay between fluid behavior and mechanical load is essential. With careful testing, appropriate fluid selection, and attention to internal sealing, even legacy machines like the 515C can be brought back into reliable service.