Allison Automatic Transmission

Torque Converter Diagnosis Procedure
The torque converter clutch (TCC) is applied by fluid pressure, which is controlled through the converter flow valve by the F trim solenoid. The converter flow valve and the F trim solenoid are located inside the automatic transmission assembly.

Torque Converter Stator
The torque converter stator assembly can have two different malfunctions.
^ The stator assembly freewheels in both directions.
^ The stator assembly remains locked up at all times.

Poor Acceleration at Low Speed
If the stator is freewheeling at all times, the car tends to have poor acceleration from a standstill. At speeds above 50-55 km/h (30-35 mph), the car may perform normally. For poor acceleration, you should first determine that the exhaust system is not blocked, and the transmission is in FIRST range when starting out.

If the engine freely accelerates to a high RPM in NEUTRAL, you can assume that the engine and the exhaust system are normal. Inspect for poor performance in DRIVE and REVERSE in order to help determine if the stator is freewheeling at all times.

Poor Acceleration at High Speed
If the stator is locked up at all times, performance is normal when accelerating from a standstill. Engine RPM and vehicle speed are limited or restricted at high speeds. Visual examination of the converter may reveal a blue color caused from overheating.

You should be able to turn the race clockwise, but should have difficulty in moving the race counterclockwise, or you may be unable to move the race at all.

Whine Noise

Important: Do not confuse this noise with pump whine noise, which is usually noticeable in PARK, NEUTRAL and all other gear ranges. Pump whine will vary with line pressure.

You may notice a torque converter whine when the vehicle is stopped and the transmission is in DRIVE or REVERSE. This noise will increase as you increase the engine RPM. The noise will stop when the vehicle is moving or when you apply the torque converter clutch, because both halves of the converter are turning at the same speed.

Perform a stall test to make sure the noise is actually coming from the converter.
1. Bring the vehicle to a complete stop using the service brake.
2. Ensure that the engine is at low idle RPM.
3. Put the transmission in P, PARK.
4. Engage the P, PARK, range by slowly releasing the service brake.
5. Apply the emergency brake and/or parking brake, if present, and ensure it is properly engaged.
6. If the vehicle will be unoccupied with the engine running, chock the wheels and take any other steps necessary to keep the vehicle from moving.
7. Place your foot on the brake.
8. Place the range selector in DRIVE.

Notice: You may damage the transmission if you depress the accelerator for more than 6 seconds.

9. Depress the accelerator to approximately 1,200 RPM for no more than 6 seconds. Listen for torque converter noise. A torque converter noise will increase under this load.

Torque Converter Clutch Shudder
The key to diagnosing TCC shudder is to note when it happens and under what conditions.

TCC shudder which is caused by the transmission, should only occur during the apply or release of the converter clutch. Shudder should never occur after the TCC piston is fully applied.

If the shudder occurs while the TCC is applying, the condition could be within the transmission or the torque converter. Something is causing one of the following conditions to occur:
^ Something is not allowing the clutch to become fully engaged.
^ Something is not allowing the clutch to release.
^ The clutch is releasing and applying at the same time.

One of the following may be causing the conditions to occur:
^ Leaking turbine shaft seal rings
^ A restricted release orifice
^ Defective friction material on the TCC piston

If Shudder Occurs After TCC has Applied

Important: If shudder occurs after the TCC has applied, most likely there is nothing wrong with the transmission.

As mentioned above, the TCC is not likely to slip after the TCC has been applied. Engine conditions may go unnoticed under light throttle and load, but they become noticeable after the TCC apply when going up a hill or accelerating. This is due to the mechanical coupling between the engine and the transmission.

Once the TCC is applied, there is no torque converter, fluid coupling, assistance. Engine or driveline vibrations could be unnoticeable before TCC engagement.

Inspect the following components in order to avoid misdiagnosis of TCC shudder. An inspection will also avoid the unnecessary disassembly of a transmission or the unnecessary replacement of a torque converter.
^ Spark plugs-Inspect for cracks, high resistance or a broken insulator.
^ Plug wires-Look in each end. If there is red ozone dust or a black carbon substance present, the wires are bad. Also, inspect for a white discoloration of the wire. This indicates arcing during hard acceleration.
^ Coil Inspect for black discoloration on the bottom of the coil. This indicates arcing while the engine is misfiring.
^ Fuel injector-The filter may be plugged.
^ Vacuum leak-The engine will not get the correct amount of fuel. The mixture may run rich or lean depending on where the leak occurs.
^ Exhaust gas recirculation (EGR) valve The valve may let in too much or too little unburnable exhaust gas and could cause the engine to run rich or lean.
^ Manifold absolute pressure (MAP) or mass air flow (MAF) sensor - possibly a vacuum leak-The engine will not receive the correct amount of fuel for proper engine operation.
^ Carbon on the intake valves-Carbon restricts the proper flow of air/fuel mixture into the cylinders.
^ Flat cam Valves do not open far enough to let the proper fuel/air mixture into the cylinders.
^ Oxygen sensor-This sensor may command the engine rich or lean for too long.
^ Fuel pressure - Fuel pressure may be too low.
^ Engine mounts-Vibration of the mounts can be multiplied by TCC engagement.
^ Axle joint-Check for vibration.
^ Throttle position (TP) sensor The TCC apply and release depends on the TP sensor in many engines. If the TP sensor is out of specification, the TCC may remain applied during initial engine loading.
^ Cylinder balance-Malfunctioning piston rings or poorly sealed valves can cause low power in a cylinder.
^ Fuel contamination-Fuel contamination causes poor engine performance.

Torque Converter Evaluation and Diagnosis
Replace the torque converter if any of the following conditions exist:
^ External leaks appear in the hub weld area.
^ The converter hub is scored or damaged.
^ The converter pilot is broken, damaged, or fits poorly into the crankshaft.
^ You discover steel particles after flushing the cooler and the cooler lines.
^ The pump is damaged, or you discover steel particles in the converter.
^ The vehicle has TCC shudder and/or no TCC apply. Replace the torque converter only after all hydraulic and electrical diagnoses have been made. The converter clutch material may be glazed.
^ The converter has an imbalance which cannot be corrected. Refer to Flexplate/Torque Converter Vibration Test (6.6L) Flexplate/Torque Converter Vibration Test (8.1L). Component Tests and General Diagnostics
^ The converter is contaminated with engine coolant which contains antifreeze.
^ An internal failure occurs in the stator race.
^ Overheating produces heavy debris in the clutch.
^ You discover steel particles or clutch lining material in the control main filter or suction filter, or on the magnets, when no internal parts in the unit are worn or damaged. This condition indicates that lining material came from the converter.

Do Not Replace the Torque Converter if you discover any of the following symptoms:
^ The oil has an odor or the oil is discolored, even though metal or clutch facing particles are not present.
^ The threads in one or more of the converter bolt holes are damaged. Correct the condition with a new thread insert.
^ Transmission failure did not display evidence of damaged or worn internal parts, steel particles or clutch plate lining material in the unit and in the control main filter or suction filter.