Automatic Transmission
12 LessonsTorque converters, planetary gears, solenoids, and modern automatic transmission diagnosis.
Overview
Automatic transmissions are the most complex mechanical assemblies in the vehicle. This module covers torque converter operation, planetary gear sets, hydraulic circuits, electronic solenoids, TCM logic, and the diagnostic approach to shift quality complaints, slipping, and harsh engagement.
Key Components
- Torque converter and lockup clutch
- Planetary gear sets
- Clutch packs and bands
- Valve body and solenoids
- Transmission Control Module (TCM)
How It Works
The torque converter uses fluid coupling to transfer power from the engine to the transmission. Inside, planetary gear sets provide different gear ratios by holding, driving, or freeing different elements. The TCM controls shift solenoids that direct hydraulic pressure to engage the correct clutch packs for each gear.
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Join the Nation — FreeCommon Problems
- Torque converter shudder on lockup
- Delayed engagement from worn clutch packs
- Harsh or erratic shifting from solenoid failure
- Transmission overheating from restricted cooler
- Fluid leak from axle seals or pan gasket
Diagnostic Tips
- Check fluid level, color, and smell first — always
- Line pressure test reveals pump and clutch pack condition
- Solenoid resistance test compared to spec
- Scan tool transmission data: TFT, line pressure, solenoid commands
Related Systems
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