Exploring Torque Converters and Some Common Repair Problems

The function of a torque converter is to transfer rotating power from the engine or electric motor to a rotating driving load. It essentially takes the place of a conventional clutch and pressure plate used with a stick shift transmission. These come in a variety of types used with different transmissions in modern vehicles. Without this mechanism, your transmission is inoperable.

How Does a Torque Converter Work?

For demonstration purposes, imagine two fans. Put both fans facing one another and turn one on. When the air begins to move through the blades of the unpowered fan, the blades will begin to turn. Using a piece of cardboard, you can redirect the airflow and speed of the unpowered fan. In a real converter there are stators that are adjusted by the number of blades or by redirecting the fluid flow by angling the blades in 2 1/2-degree increments.

What is the Function of the Torque Converter?

This is the part of the transmission that takes the place of the clutch. It does this by multiplying the torque generated by the engine. It absorbs the torsional vibration of the engine and drivetrain through the transmission fluid. Acting as the flywheel, it smoothes out engine rotation as the inertia helps maintain rotation of the crankshaft between the piston power pulses. The rear hub of the transmission drives the transmission oil pump supplying fluid to the hydraulic system.

What is a Stall Test?

The stall test checks the ability of the converter to hold torque and the operation of the one-way clutch. You can begin the test by checking the level and the condition of the fluid. Put a chock behind the wheels and set the parking brake. Start the engine and put the transmission in drive. Holding down the brake pedal firmly, press the accelerator to the floor for a maximum of five seconds while monitoring the maximum revolutions per minute (rpm). This is referred to as the stall speed. If this is lower than specifications for the engine, the clutch is slipping. If higher, the transmission is slipping.

What Are Common Problems That Arise?

Torque converter problems are varied. Worn needle bearings in the torque converter produce noise. To prove this, when the engine is in neutral the noise disappears. The clutch can jam. The converter cannot circulate the fluid properly between the impeller and the turbine, causing a lack of power when the engine reaches highway speeds. The clutch can lock and cause the fluid and engine to run hot. A one-way clutch can also fail to hold its position, allowing freewheeling in both directions. In this case, the torque converter cannot multiply torque normally and the vehicle will not accelerate properly. Replacing the torque converter is the most common solution.

Are the Newer Model Automatics Better?

Several late-model automatics have lockup torque converters to improve fuel economy. If this fails, there will be slipping and fuel economy will drop. When the car vibrates just before or after lockup, this is called lockup shudder. The converter is one of many possible culprits. Transmission drainback is when fluid drains out of the converter and back into the transmission. Fluid level is normally full in the converter when the engine is off. Worn bushings can allow drainback, which feels as if the transmission is slipping when accelerating.

Without torque converters an automatic transmission will not perform correctly. Slippage, over-heating, and shuddering are all symptoms of problems with this mechanism that will require professional auto repair. Properly functioning converters help with fuel economy and acceleration, and prevent power loss. Improperly functioning converters can cause damage to your transmission and your engine.