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How does a Torque Converter Work

Medha Godbole
A torque converter is an altered form of fluid coupling. This device is used to transfer power from a prime mover, like an electric motor, to a circulating driven load. Go through this story to gain knowledge about the working process of this machine.
Ever wondered how does a gearbox works in a car, and how the gear ratios are changed automatically while the vehicle is in motion? The answer is the torque converter. It is a significant part of all heavy vehicles, marine propulsion systems, and industrial power transmission systems.
A torque converter is a type of a hydrodynamic device, which is required to carry the mechanical power, generated through its rotation. It specifically transfers power from an internal combustion engine or an electric motor, to a load driven by the rotation of a machine or the carrier. It serves as a mechanical clutch, by separating the load from the power source.


The important rotating parts of a torque converter are:
  • A pump, which is driven mechanically by the prime mover.
  • A turbine, which propels the load.
  • A stator, which is a liaison between the pump and the turbine. The oil flow returning from the turbine to the pump is modified by this part.
Basically, there are three operational stages regarding the functioning of this device.


This happens when the pump is being propelled, and is driven by the prime mover, but the turbine is still not driven into rotation. In vehicles like cars, this happens when the converter is in gear, but the vehicle's movement has been stalled, as the driver has applied the brakes. As the vehicle begins to move, there is a large difference between the pump and the turbine speeds.


In this stage, the vehicle or the load has started moving faster. Still, there is a big gap between the speed of the turbine and the pump. Here, one can find some torque multiplication, which refers to the torque (the characteristic of force, to rotate an object about an axis) provided to the turbine output shaft.
In this stage, it is less than the stall conditions. However, the multiplication depends upon the difference between the speed of the turbine and the pump. It is also dependent upon the machine's design.


This phase occurs, when the turbine has attained about 90% of the pump speed. Now, there is hardly any torque multiplication. In the new age automobiles, this is where the lockup clutch is used. Coupling refers to a process of enhancing fuel efficiency. The converter acts like a mechanical clutch, separating the load and the power source.

Symptoms of a Bad Converter

The first sign that a torque converter has gone kaput, is the stalling of the vehicle while in forward or reverse gear, simply slowing it down to a complete stop. Another symptom is that of the converters experiencing shudders, when in the overdrive mode.
A bad converter can prevent a vehicle from generating sufficient power. Weird sounds, like the ones resembling grinding or whistling, can be heard when a converter is dysfunctional. When the gearbox cannot give a proper gear switching, it can be safely assumed that this device is not working properly.


  • Overheating: It is the most common issue that occurs in a torque converter. Persistent high levels of transmission slippage, hampers the converter's ability to dissipate heat. This causes damage to the elastomer seals, retaining fluid in the converter.
  • Seizures in Stator Clutch: Many times, this is caused by major loading and consequent disturbance of the clutch components.
  • Ballooning: Persistent application under excessive loading, coupled with running the converter at a very high RPM, can distort the shape of its housing. This is called ballooning. It can cause the converter housing to burst or rupture.
  • Deformation of Blade/ Turbine: Excessive heating of the converter, can lead to the breakage or deformation of the turbine and pump. They can be separated from their hubs or annular rigs, or may break in fragments.