RD690 Throttle Shaft Seal Leak: Diagnosis and Repair

[MikePhua]

The Mack RD690, a robust truck model known for its durability and performance, has been a staple in the heavy-duty trucking industry. However, like all mechanical systems, it is susceptible to wear and tear over time. One common issue reported by operators is fuel leakage around the throttle shaft of the fuel injection pump. This problem can lead to fuel wastage, potential fire hazards, and engine performance issues if not addressed promptly.
Understanding the Throttle Shaft Seal
The throttle shaft in a diesel engine's fuel injection pump controls the amount of fuel delivered to the engine. Seals around this shaft prevent fuel from leaking out of the pump. Over time, these seals can degrade due to factors like age, fuel quality, and operating conditions, leading to leaks.
Symptoms of a Throttle Shaft Seal Leak
Operators may notice several signs indicating a throttle shaft seal leak:

• Visible Fuel Leakage: Fuel pooling around the base of the throttle shaft.
  
• Fuel Odor: A strong smell of diesel fuel, especially after engine shutdown.
  
• Engine Performance Issues: Irregular idling, hard starting, or increased smoke emissions.
  
• Increased Fuel Consumption: A noticeable drop in fuel efficiency.
  

Diagnosing the Leak
To confirm a throttle shaft seal leak:

1. Visual Inspection: Examine the area around the throttle shaft for signs of fuel leakage.
   
2. Operational Test: With the engine running, observe any fuel dripping or pooling around the shaft.
   
3. Pressure Test: In some cases, applying slight pressure to the fuel system can help identify the source of the leak.
   

Repair Options
Addressing a throttle shaft seal leak can be approached in several ways:

1. Seal Replacement: For minor leaks, replacing the worn seal may suffice. This involves removing the throttle housing, extracting the old seal, and installing a new one.
   
2. Bushing Kit Installation: In cases where the throttle shaft has worn grooves, installing a bushing kit can restore a proper seal.
   
3. Complete Pump Rebuild: If the pump has significant internal wear, a full rebuild may be necessary. This process involves disassembling the pump, replacing all worn components, and reassembling it to factory specifications.
   

Preventive Measures
To prolong the life of the throttle shaft seal:

• Regular Maintenance: Adhere to the manufacturer's maintenance schedule, including timely oil and fuel filter changes.
  
• Quality Fuel: Use high-quality, clean diesel fuel to reduce contaminants that can degrade seals.
  
• Proper Storage: Store the vehicle in a dry, temperature-controlled environment to prevent seal deterioration.
  

Real-World Example
A Mack RD690 operator reported a gradual increase in fuel consumption and noticed fuel pooling around the throttle shaft. After conducting a visual inspection and confirming the leak, the operator opted to replace the throttle shaft seal. Post-repair, the truck's fuel efficiency improved, and the fuel leakage ceased, demonstrating the importance of timely maintenance.
Conclusion
A throttle shaft seal leak in the Mack RD690 is a manageable issue with proper diagnosis and repair. By understanding the symptoms, diagnosing the problem accurately, and choosing the appropriate repair method, operators can ensure their vehicles remain in optimal condition, minimizing downtime and maintenance costs.