What Happens When a Torque Converter Goes Bad?

How a Torque Converter Works

To understand what happens to a torque converter, it is important to understand the operation. The torque converter is bolted directly to the flexplate on the back of the engine. The flexplate is bolted to the rear of the crankshaft. The splined end of the transmission input shaft is inserted into the torque converter's splined discs. This is the only connection for the transmission to the engine. The torque converter has four distinct sections: the pump, (which is the housing), the stator, the turbine and the one-way clutch.

The easiest way to describe what takes place in the torque converter is to imagine two electric fans facing each other. Turn one fan on and leave the other fan off. As the operating fan works, it will begin to turn the fan that is off. It will begin slowly then pick up some speed, depending on how fast the operating fan is working. The fan that is off but turning from the wind force from the operating fan is called the driven gear. It is driven by the first fan. This driven gear is the turbine. In this illustration, the fan that is on is the engine and the driven gear or fan is the turbine. This is how the vehicle can stop without stalling the engine. With low rpm, there is little pressure on the driven fan. Since it is not directly attached to the engine, it can slow down without causing difficulty.

In the torque converter, the transmission is attached to the turbine through the splined shaft. The turbine is not attached to the torque converter. It is free floating and attached only to the input shaft. Between the torque converter housing and the turbine is a stator. As the engine turns, the torque converter housing or pump builds hydraulic pressure. This hydraulic pressure depends on how fast the engine is turning (rpm).

The stator is designed to increase the hydraulic pressure to the turbine while reducing the speed of the turbine and producing more torque in the process. As the speed of the engine increases, the pressure increases quickly and the stator multiplies the pressure to the turbine causing the vehicle to accelerate. At a cruising speed of 45 miles per hour or better with steady rpm, the lock up will occur making the ration 1:1 between the engine and transmission. The engine is turning as fast as the transmission at this point. As soon as acceleration is needed, it will drop out of lockup and return to about 80 percent efficiency to prevent lugging the engine. This is the same as an overdrive and saves fuel.

When a Torque Converter Goes Bad

When a torque converter goes bad, one of two things will normally happen. If the torque converter was overpowered by a larger than stock engine or by pulling something very heavy, the vanes inside the torque converter will bend. When this happens, it feels like the transmission is slipping. It takes a lot of gas to get the vehicle moving. In a severe case, the vanes could be bent so much that the car will just rev up, but it will not go anywhere.

The other resulting failure will cause a higher than stock stall by bending the vanes just enough. When the vehicle takes off from a stop, you will notice that the rpm will raise higher than normal before the vehicle begins to move. This however, will still work fine once the turbine has caught up. It indicates an impending problem.