Torque Converter Lockup – A Precise Guide

In the operation of newer automatic transmissions, one of the things that people easily overlook or miss is torque converter lockup. Present transmissions we drive are computer controlled. And this converter locks and unlocks without you knowing what happened in this transmission.

There are two types of torque converter lockup which are the lock-up torque converter vs. non-lock-up. In the late 1940s, the lockup converter was introduced, but because of the extra cost, it could not become popular until the late 1970s. This was when there was an energy crisis that resulted in the more efficient operation of automatic transmissions.

If you are not familiar with how to identify a lockup torque converter or what a torque converter lockup is, or what it does, an easy answer is that the lockup clutch removes the stress from the fluid coupling of the torque converter. It also helps reduce the heat amount generated when you drive at high speeds.

Let us find out below what torque converter lockup is and other things that you should know about torque converter lockup.

torque converter lockup problems

What is torque converter lockup?

A torque converter lockup is a type of converter with a clutch. When this clutch is engaged, it results in the engine locking to the transmission input shaft, which then causes a one-to-one drive ratio. People use a torque converter lockup because it provides fuel economy. This allows you to ensure you use minimal fuel while cruising your ride.

The torque converter lockup became popular when it was discovered that automatic fuel transmissions are less fuel-efficient than manual transmissions. Old torque converters usually lead to a loss in RPM between the input shaft and the gearbox’s crankshaft. Since car manufacturers had to meet up with the demand of the government, they accordingly made automatic transmissions that would help in improving fuel economy.

The overdrive ensures that the engine turns when in lower revolutions per minute (RPM) or while the vehicle is accelerating at a fast speed. Though this provided an advantage, all was not rosy as the engine slowly turned since it resulting in a torque converter slippage. When the torque converter slips, it would generate heat which can potentially and negatively affect the transmission and converter.

The resulting heat has an impact on fuel economy, which overturned the reason it was initially used. This resulted in a lock-up of the converter which helps in curbing the slippage while also improving fuel economy and reducing heat. There are also cases when people find out the torque converter going in and out of lock-up.

How to tell if the torque converter is locking up

When you perform a torque converter lock-up test, you intend to find out if your torque converter is locking up. All you have to do is look at the RPM reading on your car’s dashboard.

If you notice that the RPM reading constantly rises, though you are not speeding up your car, then that is a sign of a torque converter locking up. Another sign could be when your engine is talking, even when your car is at a complete halt.

torque converter lockup symptoms

How to fix a torque converter lockup problems

As a piece of sensitive equipment, the torque converter is filled up with automatic transmission fluid which creates the hydraulic pressure needed to properly function. Finding out how to test the torque converter shudder is one way of knowing that the issue is from the torque converter clutch.

There are several signs to tell you there is a torque converter lockup problem. The torque converter lockup symptoms and how to fix a locked-up torque converter are:

● Vehicle unable to shift

One of the major signs that tell you the torque converter is locking up is when your car is unable to shift to a particular gear. When you cannot get your car to drive forward or get into reverse, then there is a high probability that there is a problem with our torque converter.

● Acceleration loss

Shuddering is one of the torque converter lockup solenoid symptoms. When you feel that your car is more sluggish than it normally is, or you feel a physical shuddering whenever you place your leg on the gas pedal like the car is struggling to accelerate than it normally would.

This could be that your car has a transmission issue, and the torque converter could be the likely cause. Find out how to test a torque converter before installing a new one. This will ensure that there are no problems.

● Overheating transmission

Similar to the engine, the transmission has a sensitive temperature gauge that warns you when the transmission is overheating. Overheating is a huge concern, so you should ensure that your car is checked by a transmission specialist without hesitation. The cause could be a failing torque converter or other internal damage that should be addressed.

Let us briefly discuss a bad torque converter vs. bad transmission since there is a correlation. A bad torque converter often results in transmission slip or difficulty in gear engagement. On the other hand, bad transmission could result in the vehicle lurching or kerning when you change gears.

● Slipping between gears

Automatic gears should be able to smoothly shift between gears. When you quickly accelerate and decelerate, you should be able to feel this to some extent.

But, you can also feel that your car is slipping when it shifts gears or even find out that it is unable to stay in a particular gear. When you feel the shifting is strange or rough, there is a chance that the torque converter is locking up.

● Bad transmission fluid

When you check your transmission fluid, and you notice it is milky, dark, burnt, or has debris such as metal shavings, you should get the transmission serviced immediately. This might be the only thing you need to ensure fresh fluid runs through the system again.

It might also be a sign of a torque converter or transmission issue. This is a common torque converter not locking up symptoms. So, ensure you get an inspection from an expert transmission technician.

● Transmission fluid leak

Transmission fluid leak is very important to the performance and health of your torque converter and also the transmission system. The seals of a torque converter can get worn out as time goes on and also be easily damaged. These are some common causes of transmission fluid leaks.

When a transmission fluid leaks, you should not take chances. It is usually an early warning that there is a problem that could result in huge internal damage if you don’t take steps to resolve them.

Frequently Asked Questions-FAQs

1. At what RPM does a torque converter lock up?

A torque converter lockup reduces energy loss while also improving the miles per gallon (mpg). Usually, the torque converter lockup speed feature does not engage till the car gets to around 40 miles per hour which are around 1600 RPM.

2. What happens when a torque converter stays locked up?

Different from other converters, the lockup converter has a clutch. When the clutch is engaged, the engine is locked to the transmission input shaft. This gives a one-to-one drive ratio. A type of torque converter failure is when a one-way torque clutch does not release. A car with a one-way clutch that does not release will accelerate normally but at decreased top speed.

This failure would result in around 30 to 50% of reduced mpg. Top speeds might be reduced to 40 or 50 mph. Sometimes, it might be that the switch failed and therefore resulted in a constant signal to the converter to lock up. So, you should properly check this before you consider replacing your torque converter clutch solenoid.

If you experience a reduction in voltage feed to the transmission, the solenoid is not usually triggered. Sometimes, it might be possible but not very likely that there might be a problem with the brake switch since the fourth gear switch should have disabled the circuit when the transmission downshifts out of overdrive.

3. What happens when a torque converter doesn’t lock up?

Apart from the evident speed sensing indicator, a torque converter might not lock up for the following reasons:

  • When the temperature is very cold: Many converters would not lock up till the coolant gets to around 120°F.
  • When the converter is under a low engine vacuum: A heavy part-throttle acceleration is an added power demand that might result in an engine lugging. So, you can stop engine lugging, which usually results in serious engine damage using a sensor that determines when there is a low manifold vacuum.
  • When the overdrive unit is locked out: The torque converter feature will be locked out when the automatic overdrive is locked out; normally, the overdrive lockout is used when pulling heavy loads, so logically, the converter is locked out.

4. How do you unlock a torque converter?

To unlock a torque converter, you have to disconnect the transmission downshifts out of the 4th gear or the +12 volts. In some cases, when you apply brakes, there is a cruise control system that helps in disconnecting the +12 volt lockup module.

This allows the converter to leave the lock-up mode and let the vehicle accelerate easily back to speed before the lock-up restarts.

5. Can you shift with the torque converter locked?

Shifting with a torque converter locked doesn’t damage the transmission since the transmission control unit is made to not let this happen. This only happens if the transmission is made to be able to handle it. But, when you modify your transmission, then that is another story entirely.

Final Words

Car lovers are always more concerned about the technicalities of their cars. And one of these technical aspects of cars that would interest car lovers is the curiosity of knowing the working of a torque converter lockup. Many car geeks have been interested in this converter because it creates a better life for the transmission and also its fuel efficiency.

Every modern automatic transmission embedded model is designed with a torque converter lockup. As an innovative mechanism, it has been making rounds in the market for the efficiency that it provides. With its several elements, the torque converter lockup is being manufactured with the future in mind.

Future torque converters are predicted to take into consideration smooth, efficient, and comfortable rides by ensuring that they have a tuned control strategy that considers the torque demand of every vehicle. While also integrating this knowledge into the type of transmissions and cars that consumers would buy.


Hi there, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanic (Both Heavy Commercial and Private Cars). I worked as a Mechanic and Mechanic Supervisor for over fifteen years at Global Rebound Automotive companies - Toyota, TATA, BMW, Nissan, TVs, and Others. Now, I enjoy my new role of leading a team of automotive experts (in their respective fields) and publish new content on a regular basis on my website and social media.

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