The torque converter is a critical component in an automatic transmission system. It allows the transmission to switch smoothly between gears and provides hydraulic power to enable shifting. Like any complex mechanical part, torque converters can develop issues over time. Identifying problems early is key to avoiding major transmission failure. This guide will outline the most common torque converter problems and how to diagnose them.
What Does The Torque Converter Do?
First, let’s review the role of the torque converter. This doughnut-shaped device sits between the engine and transmission. It uses automatic transmission fluid (ATF) to couple the engine crankshaft to the transmission input shaft. The torque converter has three main purposes:
- Multiply engine torque to provide more power for acceleration
- Allow the engine to spin independently of the transmission when idling to prevent stalling
- Smooth out power delivery between the engine and transmission
The converter uses impeller, turbine, and stator blades spinning in ATF to transfer and multiply rotational force. As engine speed increases, the force causes the turbine to turn, which then spins the transmission input shaft.
Common Torque Converter Issues
Here are some of the most prevalent torque converter problems:
- Slipping: Slipping occurs when the converter fails to fully couple the engine and transmission. This allows the engine RPMs to race without corresponding vehicle speed. Symptoms include lack of acceleration, high RPM with little power, and burning smell from transmission fluid.
- Shuddering: A shudder or vibration when accelerating signals potential converter damage. The vibration typically happens at certain speeds as damaged blades struggle to transfer spinning force.
- Leaking fluid: Cracked seals or loose connections can cause ATF to leak externally. Check under the vehicle for signs of dripping fluid. Low ATF level can also indicate internal converter leaks.
- Overheating: Similar to slipping, overheating results when the converter cannot properly couple the engine and transmission. This forces the transmission to work much harder, generating excess heat and accelerated wear.
- Noise: Unusual noises like whining or grinding indicate internal torque converter problems. Noises may occur when shifting gears or get louder with increased speeds.
- Failure to lock: If the converter does not lock the engine and transmission together at cruising speeds, it cannot transmit full engine power. Acceleration will be sluggish.
Diagnosing Torque Converter Issues
Pinpointing a faulty torque converter requires a few diagnostic tests:
- Stall speed test: This measures the maximum RPM the engine reaches with the brakes applied and transmission in drive. Higher than normal stall speed indicates converter slipping.
- Road test: Accelerating across a speed range may reveal slipping, shuddering, or lack of power. The converter should engage and disengage smoothly.
- Leak inspection: Check under the vehicle and inspect the transmission fluid color. Leaks or abnormal dark color signal overheating issues.
- Speedometer test: Comparing engine RPM to vehicle speed at different throttle levels will show if the converter is failing to couple properly.
- Tachometer test: Revving the engine in neutral should cause RPMs to drop smoothly when the throttle is released. Rough drops indicate converter problems.
Torque Converter Failure Modes
When torque converters fail, it’s generally due to one of these causes:
- Overheating: Fluid breakdown and seal damage from excessive heat.
- Wear and tear: Gradual damage to internal parts like impeller blades and bearings.
- Manufacturing defects: Imperfections in converter components.
- Too much torque: Heavy acceleration and hauling can overstress the converter.
- Contamination: Metal shavings or sludge in the ATF obstructing converter.
Repairing a faulty torque converter often requires full replacement. Thankfully, rebuilt or remanufactured converters are widely available at reasonable cost. Swapping out the converter may also reveal additional transmission issues that should be addressed.