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How Does a Torque Converter Work? The Fascinating Answer!

Close-up of automotive torque converter

Transmission in a car means that you can start and stop the vehicle’s movement while the engine is still running and be able to adjust the rate of speed. A clutch disconnects the gears and wheels from the engine in manual transmissions, but auto transmission uses a torque converter.

So how does a torque converter work? How is it implemented, and what happens to your car when this part breaks down? In this article, we explore the characteristics of a torque converter and why they are an essential part of an automatic transmission operation.

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How Does a Torque Converter Work?

A torque converter takes the place of a manual transmission clutch to allow the engine to turn independently of the vehicle’s drive shaft and transmission. It’s a type of fluid coupling1 with three main parts, including an impeller, turbine, and stator for fluid reversal.

But before talking about this converter, it’s essential to understand what torque is. In simple terms, torque is the potential energy created when something is wound up or twisted. It’s a force that makes a spring wire bounce back, like the wind-up toys, which move forward because of the retraction of springs.

Torque force is produced by the engine’s crankshaft in cars, allowing you to accelerate your vehicle. The more torque your engine has, the faster you can drive. A torque converter’s job is to transmit this energy between the engine as a power source to the load and transmission.

The internal components of a torque converter that are essential to its operation include:

Torque converter cutbox model
Torque converter cutbox model (Image By: No machine-readable author provided. BerndB~commonswiki assumed (based on copyright claims)., via Wikimedia Commons CC BY-SA 3.0)

The Pump or Impeller

The converter’s housing is usually bolted to the engine’s flywheel, and within are fins that make up the impeller or pump. These turn at the same speed and act as a centrifugal force generator, creating a vacuum that flings more fluid to its center.


The fluid moves a turbine connected to the transmission, and since the turbine blades are curved, it changes the direction, which causes it to spin. At the center of the torque converter is a stator, which prevents the fluid from hitting the pump to increase efficiency.


An aggressive blade design is characteristic of the stator so that it can reverse the direction of the fluid, and it’s connected to the transmission fixed shaft by a one-way clutch. As such, it spins in the opposite direction of the fluid, but at certain speeds, its operation becomes unnecessary.

That’s when, at 40mph, both the turbine and pump spin at nearly equal speed, so fluids return from the turbine’s blades, which move in the pump’s direction. Fluid strikes the back sides of the stator’s blades, which causes the one-way clutch to free-wheel, so it’s not hindering the fluid’s movement.

What Are the Different Types of Torque Converters?

Torque converter being assembled
Image By: Everyonephoto Studio, Shutterstock

The torque converter is an advanced hydraulics coupling that transmits multiple engine torques to allow your car to stop without moving or affecting the transmission. In this instance, we’re describing a hydrokinetic device, but there are also mechanical systems for continuously variable transmissions.

Mechanical torque converters that can multiply torque include the Variomatic system with a belt drive and expanding pulleys. The Lambert friction gear disk drive transmission and the pendulum-based Constantinesco torque converter are also used.

Two models of hydrokinetic torque converters commonly used today are used in earlier or later models of automatic transmission cars. These include:

1. Lock-Up Torque Converter

Because of slippage, energy loss occurs during the power transfer between an engine and transmission. A built-in locking clutch mechanism characterizes the lock-up torque converter that locks indirect connections between the input and output shaft at specific engine RPMs or speeds for better efficiency.

Lock-up torque converters reduce impelling loss with a lock-up clutch, so they become a purely mechanical coupling. However, despite cost and complexity problems after their introduction between the 1940s and 70s, they’re now universally used in automotive applications.

2. Non-Lock-Up Torque Converter

Energy loss occurs in a non-lock-up torque converter that earlier automatic transmission cars used, as these had no clutch to lock the high-speed slippage. That means the turbine spins as fast as the pump or impeller at about 90% since they’re constantly at different speeds, which results in inefficiency.

Besides applications in the automotive sector, other types or classifications of torque converters include:

3. Single-Stage Torque Converters

A single-stage torque converter has simplicity and reliability because it comes in two housing types: rotating and stationary. They have a variety of capabilities depending on the model, as seen below:

  • Simplex single-stage torque converters feature PTO drives for driving-assisted hydraulic pumps and power shift transmission applications.
  • High torque rotational converters that feature stable housings for exceptional lowering and hoisting capabilities are designed for the oil and gas industry.

4. Three-Phase Torque Converters

These employ two sets of stator or reactor blades and three turbine blade rings to increase torque up to five times the engine’s output. Three-phase torque converters are available in rotating or stationary housings and are rated for specific ranges of engines according to their design.

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Where Is a Torque Converter Used?

automatic transmission
Image Credit: RomanR, Shutterstock

Torque converters are an essential part of an automatic transmission, a fluid coupling responsible for increasing the torque output and preventing slippage using rotating elements. Many torque converters employ the lock-up clutch for cruising to improve power efficiency and eliminate generated heat.

The stator is the main component of a torque converter’s capability to multiply torque, prevent slippage and eliminate energy loss. Three stages of operation are attributed to a torque converter’s fluid transmission involving the impeller, turbine, and stator.

These include:

1. Stall

As power is provided to the impeller or pump by the engine, it doesn’t rotate while you’ve applied pressure to the brakes if you’re at a stop light, for instance. While your car doesn’t move, the engine won’t stall either since the turbines are not rotating even though the transmission is in gear.

The stall phase is temporary as the torque converter produces maximum input power, resulting in stall ratio multiplication. When your car starts to move, there’s a significant difference in the speed of the turbine and pump or impeller.

2. Acceleration

If you take your foot off the brakes while your car is in gear, acceleration happens, especially if you’ve stepped on the gas pedal. It’s characterized by a faster impeller rotation, which rotates faster than the turbine to create torque multiplication that accelerates your vehicle’s driveline.

3. Coupling

Torque buildup stops once your car reaches cruising speed and the impeller is rotating at the same speed as the turbine. A torque converter acts as a fluid coupling at this stage, and your vehicle’s automatic transmission employs the lock-up clutch to lock the pump to the turbine.

Coupling eliminates power loss to keep your car moving smoothly since the impeller gets its power from the engine. On the other hand, the turbine is connected to the output or drive shaft, which is where the transmission gets powered. You’ll feel a shudder or shaking during coupling if something’s wrong with your torque converter.

Advantages of the Torque Converter

man driving automatic transmission car
Image Credit: Alexander Tolstykh, Shutterstock

When you accelerate out of a stop, the torque converter offers your vehicle more power besides allowing it to come to a halt without its engine stalling. Modern converters multiply the engine’s torque by two or three times but only when it’s turning faster than the transmission.

At high speed, the transmission equals the engine’s speed but any difference between the two wastes power. That’s why automatic transmission cars are notorious for lower gas mileage than vehicles with manual transmissions.

The lock-up clutch provides a solution to this effect by locking the two halves of the torque converter together to improve efficiency by eliminating slippage. A significant upside of a torque converter is harvesting the kinetic energy from the rotating fluid and putting it back into the cycle for torque multiplication.

A lock-up torque converter must provide a direct 1:1 engagement between the transmission and engine due to fuel economy. The overdrive allows the engine to spin at lower RPMs during cruising speeds, but that causes increased slippage or generated heat.

Disadvantages of a Torque Converter

Torque converters can break down, and there are several ways this can pose a danger to your car or your life. For instance, continuous slippage in high levels will result in overheating, damaging the elastomer seal, which is designed to keep the transmission fluid from leaking.

If your torque converter hydraulic fluid leaks, the system will stop working, or your stator clutch will break or seize. That ultimately results in significant drops in fuel efficiency, especially if the clutch’s outer and inner elements lock together.

A broken stator clutch will go into a free spin, which means the torque converter will cease to work, rendering your car immobile or stalled. Besides driving down your gas mileage, ruined, fragmented, or deformed turbine or impeller blades can also cause the system to self-destruct violently.

Within the torque converter’s housing is significant pressure and hot transmission fluid when it’s in operation and failing can cause the component to burst. In the instance of rupturing while you’re driving, you and your passengers will be in danger of hot liquid and flying shrapnel.

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Major Problems Affecting a Torque Converter and Their Symptoms

Due to the complex nature of the parts within a torque converter’s housing, they’re susceptible to failure and will give out with prolonged usage. You can monitor some of these problems, while others require a professional diagnosis for which early detection is essential.

While detecting a problem with your car’s torque converter isn’t easy without disassembling the transmission or drivetrain, there are some symptoms to look out for. A torque converter that’s dysfunctional or worn prevents the proper pressurization of fluid and negatively impacts gear operation and vehicle function.

Signs of a problematic torque converter will include gears shifting, strange noises, shudders, fluid leakages, and higher-than-usual revs. Several symptoms of these problems and others affecting your car’s torque converter include:


Torque converters are responsible for converting engine power to the hydraulic pressure necessary to shift transmission gears, and slippage occurs when bearings and ribs cause delays in the shift. Insufficient or excessive fluid is another reason slipping will happen, and you’ll notice acceleration loss or an increase in fuel consumption.


Your car’s temperature gauge will indicate that your engine is overheating, which may suggest that fluid pressure has dropped to signify a problem with your torque converter. Once overheated, the system’s efficiency of transferring torque to the vehicle’s transmission decreases, leading to poor throttle response.

Overheating may also be caused by excessive wear and tear of internal torque converter parts, while a defective magnet or low fluid levels will cause gears to overheat.

Shaking or Shuddering

At speeds of around 30 to 45 mph, you’ll feel shuddering when the lock-up clutch starts to fail within the torque converter. It’s a noticeable shaking that feels like you’re driving over pole bumps or a rocky road, and there’ll be difficulty transitioning to direct drive.

While shuddering may start and stop for short periods, you must have your transmission checked, especially if you feel it multiple times.

Dirty Transmission Fluid

Automatic transmission fluid fills the torque converter, and when this becomes contaminated, internal parts like the stator, turbine, or impeller fins get damaged. It also leads to worn bearings, black sludge, debris, or dirt floating within the fluid.

If you’ve noticed this, change the transmission fluid, and drive around before checking for contaminants again. That will indicate damage to the torque converter or gearbox.

Higher Gear Engagement RPM or Stall Speed

Stall speed is where engine speed is high enough to transfer power to the transmission via the torque converter. It’s the speed where the converter’s operations desist from increasing engine speed since the transmission is disengaged or when you’ve stopped the car on idle.

Incorrect transfer of rotational force to the hydraulic pressure from the engine is descriptive of a defective torque converter. The lock-up speed increases since the transmission takes longer to switch on the motor, and you can tell by how fast your engine’s Revolutions per Minute or RPM is when your vehicle stops.


Due to prolonged torque converter operation under excessive load, high RPM, or abrupt loading, the external casing of your car’s torque converter can become distorted. That’s caused by the buildup of internal pressure or inertia-imposed stress and can result in ballooning or, in extreme conditions, rapture.

divider 4 Frequently Asked Questions (FAQs)

How much would it cost to replace a torque converter?

You should visit a competent repair shop if your car’s torque converter needs replacing, where you can expect costs of between $500 and $1,000, depending on your vehicle’s make and model. While self-replacement isn’t recommended, you can do so with the right tools and equipment for costs that won’t exceed $450.

What are some of the reasons a torque converter would fail?

Torque converters fail due to excess friction, damaged needle bearings, turbine blades, or transmission fluid leakage. The source of such problems includes fault seals or clutch solenoids.

Which symptoms will signify a failing torque converter?

A failing torque converter sends vibrations or shaking throughout the vehicle, especially in coupling mode, as you start moving from a stall to an accelerating position. That’s caused by slippage during an override, or you may notice lagging and vibrating even when the car isn’t moving.

Does a damaged torque converter produce any noise?

A damaged torque converter produces several sounds, including rattling, whining, and a low humming or screeching, whether your car is on halt or moving. Unless properly tuned, the complex system will adversely affect your car’s performance, durability, fuel economy, and drivetrain power.

What is the stall speed of a torque converter?

Torque converter stall speed is the maximum engine Revolutions per Minute or RPM achievable while the transmission engages in forward operating range without driveshaft motion. Using a flash stall or foot-brake stall, you can measure stall speed in an automatic transmission vehicle.

What are the significant parts of a torque converter?

Although there are a lot of gears and shafts within a torque converter, the main parts include the turbine, impeller or pump, and stator. The pump and turbine are blades similar to a fan but curved or tilted in different directions to spin fluid and produce torque.

The lock-up clutch, susceptible to breakage or seizure with excessive load, is one of the significant parts that make the system operate efficiently. It’s located within the stator assembly and is the reason the device can convert torque; since, without it, it’s only a fluid coupling.

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The torque converter uses a fluid medium to enable your car’s engine to spin independently of your transmission when starting or stopping. The pressurization of hydraulic fluid creates torque forces that necessitate transmission gear engagement and disengagement.

Knowing how a torque converter works is essential for correctly monitoring its operation since a faulty system will adversely affect gear operation and your car’s functioning. In case you suspect any problems, it’s recommended that a thorough inspection by a professional be the route by which you can isolate the root cause and reach a solution.

Featured Image Credit: jeffy11390, Shutterstock


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