Starting Troubleshooting for the 1973 International 175C Track Loader

[MikePhua]

The Legacy of the 175C and Its Mechanical Simplicity
The International Harvester 175C track loader was introduced in the early 1970s as part of IH’s industrial equipment lineup, designed for heavy-duty earthmoving, demolition, and site preparation. With a robust frame, mechanical transmission, and direct-injection diesel engine, the 175C was built for durability over finesse. It featured a torque converter drive, mechanical steering clutches, and a straightforward electrical system—making it a favorite among operators who preferred machines they could fix with basic tools and a voltmeter.
Though production numbers were modest compared to IH’s agricultural tractors, the 175C saw widespread use across North America, particularly in municipal fleets and small contractors. Today, surviving units are often found in rural yards, still pushing dirt after five decades of service.
Terminology Annotation
- Starter solenoid: An electromechanical switch that engages the starter motor when the ignition is activated.
- Diesel jumper box: A portable battery booster designed to deliver high cranking amps for diesel engines.
- Safety brake: A mechanical or hydraulic lockout system that prevents machine movement during startup or service.
- Voltage drop under load: A condition where electrical resistance causes a significant drop in voltage when current demand increases, often due to corroded connections or weak batteries.
Symptoms and Initial Observations
An operator attempting to start a 1973 175C reported hearing a single click at the starter when pressing the ignition button. The machine was in neutral, with the safety brake engaged, and both a truck battery and diesel jumper box were connected to the onboard batteries. Despite these efforts, the engine failed to crank.
This symptom—clicking without rotation—is a classic indicator of insufficient current reaching the starter motor. The click confirms that the solenoid is receiving signal, but the motor itself is not engaging, suggesting a fault in the power delivery path.
Diagnostic Steps and Electrical Testing
Before assuming starter failure, technicians should perform a series of voltage tests under load. This includes:

• Measuring battery voltage at rest (should be 12.6V or higher for fully charged batteries)
  
• Measuring voltage at the starter terminal during attempted crank (should remain above 10V)
  
• Checking ground connections between battery, frame, and starter housing
  
• Inspecting cable terminals for corrosion, looseness, or internal breakage
  
• Testing continuity across the solenoid and starter motor windings
  

If voltage collapses during cranking, the battery may be weak or the jumper box ineffective. Many modern jump boxes advertise high peak amps but fail to deliver sustained current under load. A direct connection to a running diesel truck with heavy-gauge cables often yields better results.
Starter Solenoid and Mechanical Resistance
If voltage remains stable but the starter still fails to engage, the solenoid may be internally worn or the starter motor seized. In some cases, the engine itself may be locked up due to internal damage or hydraulic lock. To rule this out:

• Attempt to rotate the engine manually using the fan blades or crank pulley
  
• Listen for resistance or grinding noises that suggest mechanical interference
  
• Remove the starter and bench test it with direct battery power
  

One technician recalled a similar issue on a 1975 IH TD-8 dozer, where the starter solenoid had corroded internally. Replacing the solenoid restored full cranking power, and the machine started immediately.
Safety Interlocks and Forgotten Switches
Older IH machines sometimes include hidden or overlooked safety switches that interrupt the starter circuit. These may include:

• Seat switches that require operator presence
  
• Transmission neutral sensors
  
• Brake lockout switches
  
• Auxiliary hydraulic lockouts
  

Operators should consult the wiring diagram or trace the starter circuit manually to identify any inline switches. A bypass test using a jumper wire from the battery to the starter solenoid can confirm whether the issue lies upstream in the control circuit.
Preventive Measures and Long-Term Reliability
To avoid future starting issues:

• Replace all battery cables with heavy-duty copper cables rated for diesel cranking
  
• Install a master disconnect switch to prevent parasitic drain
  
• Use dielectric grease on all terminals to prevent corrosion
  
• Test starter draw annually using a clamp meter
  
• Keep a dedicated jump battery on-site for cold starts
  

In one case, a county road crew retrofitted their aging IH fleet with modern gear-reduction starters, reducing cranking amperage and improving cold-weather reliability.
Conclusion
Starting problems on the 1973 International 175C are often electrical in nature, stemming from voltage drop, corroded connections, or solenoid failure. With a methodical approach—voltage testing, mechanical inspection, and circuit tracing—operators can restore functionality without resorting to guesswork. These machines were built to be repaired, not replaced, and with the right tools and mindset, even a stubborn starter click can be turned into a roar of diesel power.