Hydraulic Failure Diagnosis on the Hough H90CM Loader

[MikePhua]

The Hough Legacy and Military Variants
The Hough H90CM loader represents a specialized variant of the H90 series, originally manufactured by Hough Equipment Company, which became part of International Harvester in the mid-20th century. Known for their robust wheel loaders, Hough machines were widely used in both civilian and military applications. The “CM” designation in the H90CM likely refers to a military configuration, featuring reinforced components and a Cummins diesel engine tailored for logistics and base operations.
By the 1970s, Hough loaders had earned a reputation for durability and simplicity, with thousands deployed across construction sites, quarries, and military installations. The H90CM, with its 10,000-pound lift capacity and torque converter-driven transmission, was designed to operate in harsh environments with minimal support infrastructure.
Sudden Hydraulic Loss Across All Systems
A critical issue reported with the H90CM involves the complete loss of hydraulic function—bucket movement, steering, and drive—despite the engine running and the main shaft spinning. This type of failure suggests a disruption in the hydraulic powertrain, not just a localized leak or actuator fault.
Key terminology:

• Torque converter: A fluid coupling between the engine and transmission that multiplies torque and allows smooth gear transitions.
  
• Hydraulic pump: A gear-driven unit that pressurizes fluid for steering, lift, and drive functions.
  
• Drive shaft: A rotating shaft transmitting power from the torque converter to the transmission.
  
• Neutralizer valve: A pneumatic valve that disengages the transmission when activated, often linked to brake pedal position.
  

Initial Inspection and Misleading Indicators
Operators initially observed that the drive shaft continued to spin, leading to the assumption that the transmission was still engaged. However, the absence of hydraulic response indicated that the pump was either not turning or had lost its internal drive connection.
One overlooked culprit was the brake pedal. If the left pedal is partially depressed—due to dirt, corrosion, or mechanical interference—it can activate the neutralizer valve, preventing transmission engagement. While this explains loss of drive, it does not account for the simultaneous loss of steering and loader hydraulics.
Pump Location and Gear Drive Configuration
In the H90CM, the hydraulic pumps are mounted to the rear of the torque converter and driven by internal gears connected to the flywheel. This configuration ensures that the pumps rotate whenever the engine runs, eliminating slippage. However, if the gear coupling between the flywheel and the pump fails, the engine may run and the shaft may spin, but the pumps will not generate pressure.
A common failure point is the flange connecting the torque converter to the pump drive. In one case, four of the six bolts securing the flange had sheared, and the remaining two had backed out. This caused the pump gears to disengage, halting hydraulic flow entirely. The broken bolts were found inside the housing, along with fragments of the flange, confirming mechanical separation.
Stripped Pump Gears and Spline Wear
Another known issue with this model is stripped splines on the hydraulic pump gears. These splines transmit rotational force from the drive shaft to the pump internals. Over time, wear or misalignment can cause the splines to shear, especially under high load or poor lubrication.
Replacement gears for vintage Hough loaders are rare but occasionally surface in surplus auctions or online marketplaces. Some operators have successfully machined custom gears or adapted parts from similar IH models, though this requires precise measurement and metallurgical compatibility.
Fiber Gear Failures and Historical Context
Older loaders often used fiber gears on the flywheel to reduce noise and vibration. While quieter, these gears were prone to wear and catastrophic failure. A broken fiber gear would result in loss of both transmission and hydraulic function. In contrast, steel gears were noisier but more durable. The H90CM’s military configuration likely retained steel gears for reliability, but even these can fail under shock loads or improper torque.
Field Anecdote and Preventative Insight
During a base maintenance operation in Virginia, a military-spec H90CM suddenly lost all hydraulic function while loading gravel. The crew discovered that the pump drive flange had fractured due to bolt fatigue. The machine was trailered back to the shop, where the torque converter cover was removed and the broken components replaced. After reassembly and torque verification, the loader returned to service without further incident.
This case underscores the importance of inspecting flange bolts and pump couplings during routine maintenance. Vibration, thermal cycling, and age can all contribute to bolt fatigue and gear wear.
Recommended Solutions and Maintenance Practices
To prevent similar failures:

• Inspect torque converter flange bolts every 500 hours.
  
• Use threadlocker on flange bolts to prevent backing out.
  
• Replace hydraulic fluid annually and monitor for metal contamination.
  
• Check brake pedal linkage for free movement and full return.
  
• Verify pump rotation by observing fluid movement in the tank with the cap off.
  

Conclusion
The Hough H90CM loader, though a product of a bygone era, remains a capable machine when properly maintained. Hydraulic failure across all systems is often mechanical in origin—flange separation, stripped splines, or gear failure. With careful diagnostics and attention to historical design quirks, these machines can be restored to full functionality and continue serving in demanding environments. Their legacy is not just in steel and hydraulics, but in the ingenuity of those who keep them running.