Allison 3000/4000 Product Families - Service Issues and Diagnostics

Service Issues and Diagnostics - Fleets

A). Fluid and Filter Change Intervals

Extending fluid and filter change intervals beyond Allison recommendations and requirements can cause a variety of Transmission issues.
  • Old, dirty fluid can lead to overheating, which can diminish clutch life and harm rotating components.
  • Extended service intervals may allow dirt and debris to affect valve movement, affecting operation and generating diagnostic codes.
  • To prevent these issues, proper preventive maintenance and a clean work environment are essential.

B). Restricted Air Flow
Restricting air flow to the Transmission can increase Transmission temperature and decrease Transmission cooling capacity.
  • This can also diminish transmission fluid life.
Extended idling in range can also cause overheating.
  • Proper driver training can help prevent this – drivers should understand that Neutral should be selected whenever the vehicle will be stopped with the Engine idling for extended periods of time.

C). Technician Errors
Improper component installation or improperly performed repairs can result in high repair costs.
  • Be aware of, reference and follow approved service procedures.
  • Seek and share component, product and industry information.
  • Good training benefits everyone – fleet managers, technicians, operators and all service professionals.

D). Improper Towing
Never tow Allison-equipped vehicles with the drive wheels on the ground.
  • Always disconnect the drive line or lift the drive wheels off the ground when towing.
  • The Engine must be running to operate the Transmission pump, which sends lube to the rotating components.
  • Severe damage results from improper towing due to a lack of lube.

E). Driveline Issues
An improperly designed or poorly maintained driveline can cause drivability issues and Transmission damage.
  • Operator complaints may include vibration, noise or poor shift quality.
  • Transmission damage can occur to carrier components, bearings, clutches and more.

The Transmission is often mis-diagnosed as the root cause of failure or issues.
  • Check U-joint, slip joint, slip joint spline and installation hardware condition.
  • Check Transmission output yoke or flange condition and installation.
  • Look for damaged or dented driveshafts and indication of missing shaft balance weights.
  • Check wheels and tires for damage or imbalance issues.
  • Check for axle, axle bearing or wheel bearing issues.

F). Diagnostics
Some basic diagnostic steps apply when troubleshooting any Allison Transmission.
  • Check the Transmission fluid level and condition.
  • Visually inspect the Transmission for physical damage and leaks.
  • Inspect the Transmission Electronic Control system wiring harness and connectors for damage.
  • Check all vehicle systems for obvious damage and problems – performance issues which may seem related to the Transmission are sometimes caused by other vehicle systems.

Have available and understand how to use the Troubleshooting Manual applicable to the installed Transmission Electronic Control system.
  • Separate manuals are available for the different Electronic Control systems, from legacy WTEC controls to the latest Generation Controls version.
  • Recognize the installed Electronic Control system and reference the appropriate Troubleshooting Manual.

Use Allison DOC® to gather basic diagnostic information.
  • Check for DTCs.
  • Verify the TCM is receiving proper voltage.
  • Verify the TCM is recognizing appropriate input, turbine and output speed signals.

If DTCs are logged:
  • Write down the DTCs.
  • Save the DTC Failure Records if available, use this data to determine the attained Transmission range and vehicle operating variables that existed when the DTC was set.
  • Use the Troubleshooting Manual to understand the general conditions causing the DTCs.
  • If it makes sense for the situation, attempt to clear the DTCs and operate the vehicle.
  • If cleared DTCs reset, the issues still exist and must be diagnosed following the detailed procedures in the Troubleshooting Manual.

If no DTCs are logged:
  • Use the Allison DOC® Data Monitor feature to check for active Shift Inhibits.
  • Reference the Troubleshooting Manual’s "General Troubleshooting of Performance Complaints" section.


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