A torque converter is the fluid coupling between the engine and an automatic transmission. It lets the engine idle while the vehicle is stopped in gear, multiplies engine torque when pulling away, and at cruising speed locks up with an internal clutch so engine and transmission turn together without slipping. It does the job a clutch pedal does in a manual car, but automatically and through fluid.
How a torque converter works
- Impeller (pump): bolted to the engine through the flexplate, it spins and flings transmission fluid outward.
- Turbine: connected to the transmission input shaft, it is driven by the moving fluid.
- Stator: sits between them on a one-way clutch and redirects fluid returning from the turbine so it helps the impeller, which is what multiplies torque at low speed.
- Lockup clutch: the torque converter clutch (TCC) locks the turbine to the converter housing at cruise, removing slip to improve fuel economy and reduce heat.
Torque multiplication and stall speed
When the turbine turns much slower than the impeller, as when pulling away, the stator’s redirected flow multiplies torque. Stall speed is the engine speed at which the converter will let the engine turn against a held transmission before the vehicle moves. A higher-stall converter lets the engine reach its power band before the car launches, which is why performance builds use them; our guide what is a stall converter? explains how to choose one.
Why the torque converter matters for the transmission
The converter also drives the transmission’s pump, so it plays a part in keeping fluid pressure up. A failing converter can send debris through the transmission, which is why a converter is normally replaced along with a transmission. Every replacement transmission we carry is supplied with a torque converter.
Signs of a bad torque converter
- Shudder or vibration at steady speed as the lockup clutch engages; see torque converter shudder.
- Slipping or poor acceleration, with engine speed rising without matching speed.
- Overheating transmission fluid.
- Stalling when coming to a stop, if the lockup clutch fails to release.
- Whining or grinding noises, or a lockup code such as P0740 for the TCC circuit.
More detail: bad torque converter symptoms.
Torque converters and transmissions we carry
For LS-powered GM vehicles with a 4L60E or 4L65E we carry a billet torque converter with a 2800-3200 stall ($998.00). Complete transmissions for Chevy, GMC, Ford and Dodge/Ram, each supplied with a torque converter, are listed by code on our transmissions page.
More guides: torque converter lockup · how long a torque converter lasts.
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