Torque converters are integral parts of the drive trains on automatic vehicles, and although most torque converters are designed to last the life of the vehicle, mechanical failures of internal parts can necessitate the replacement of a torque converter on occasion. Below, we detail how a torque converter functions, common symptoms of a faulty torque converter, some tips for replacing your torque converter, and our recommendations for the best torque converter brands.
Function Of A Torque Converter
Torque converters have two functions: the first is to transmit engine power to an automatic transmission, and the second is to allow the engine to rotate freely when the transmission is in drive, but the vehicle is stationary.
In terms of operation, a torque converter consists of a steel shell that is attached to the engine and encloses an impeller (aka turbine) that is connected to the transmission input shaft. In practice, both the outer shell and the impeller feature fins or blades that face each other. As the engine spins the shell, the blades in the shell pick up transmission fluid and fling it against the opposite-facing blades of the impeller, thereby imparting a rotary motion to the impeller, which then transfers that motion to the transmission.
As a practical matter, and although the clearance between the two sets of opposing blades is relatively small, the effective transfer of engine power to the transmission is wholly dependent on the shear strength of the transmission fluid. Therefore, some torque is lost since some transmission fluid necessarily escapes through the gap between the opposing blades.
This loss of torque is commonly known as “slippage”, and on older vehicles, this came with a fuel consumption and performance penalty of up to 10% as compared to a similar vehicle with a manual transmission. To combat this as well as reduce emissions, almost all modern torque converters are now fitted with hydraulically operated mechanical clutches that can lock the shell to the impeller, thus creating a solid mechanical link between the engine and the transmission.
However, while a solid link between the engine and transmission eliminates slippage and increases fuel economy while reducing emissions at the same time, a solid link also means that gearshifts can be harsh and uncomfortable. To reduce this effect, transmission control modules can modulate the hydraulic pressure that activates the lock up clutch via a microprocessor-controlled solenoid to induce varying amounts of clutch slippage under certain conditions, such as during gearshifts under high rates of acceleration. In fact, modern torque converter lock-up clutch control algorithms are now so refined that automatic gearshifts on most vehicles are seamless and almost undetectable, which greatly improves the driving experience even on low-end vehicles.
Common Symptoms Of A Faulty Torque Converter
Although it should be noted that some of the symptoms of failing torque converters are similar to those of failing transmissions or transmission control units (TCU’s), common symptoms of a failed or failing torque converter could include the following:
Assuming that the transmission itself is free of defects, the transmission fluid is serviceable, and that the fluid level is not low, excessive slippage is more likely to be evident under high-torque conditions. This means that you’ll notice it most under heavy acceleration.
Possible causes could include insufficient hydraulic pressure, a failed or failing lock up clutch control solenoid, or excessive wear of the lock up clutch itself that prevents full lock up under high torque conditions.
The most likely cause of a torque converter overheating is prolonged slippage of the lock up clutch as the result of towing trailers, boats, etc., that are too heavy for the towing vehicle. Most other causes of overheating are usually related to faults outside of the torque converter.
Some types of mechanical failures of rotating components inside torque converters can cause imbalances to develop, with the resulting vibrations usually varying with engine speed.
Intermittent or cyclical failures of the lock up clutch can cause shuddering as the lock up clutch engages and disengages rapidly. This is rarely caused by mechanical failures of the clutch; the most common cause is related to the clutch control solenoid, rapidly fluctuating hydraulic pressure, or defects in the clutch’s control system.
Increased Stall Speed
Since the purpose of the lock-up clutch is to provide a mechanical link between the engine and the transmission, the engine will not be able to run at idle or low speeds if the clutch remains engaged, or does not disengage fully. Thus, depending on the degree of permanent clutch engagement, the engine may either not idle at all when the transmission is in gear and the brakes are applied, or it may stall at a higher than usual speed.
Broken, worn, or damaged bearings can cause whirring, whining, rumbling, or grinding sounds, while broken impeller blades can cause knocking or rattling sounds. In cases where impeller and shell blades touch as the torque converter rotates, sounds may vary from soft clinking, to rattling, to loud knocking noises that may or may not vary with engine speed.
Replacing A Torque Converter
Replacement of any torque converter requires at least the removal of the transmission from the vehicle, and sometimes, the removal of the engine and transmission as an assembly for purposes of convenience. Considering the complexity, we will forego providing an overview of steps in favor or providing a few tips to make the project go a little smoother for you. Before starting this project, you should make sure you are comfortable with the level of commitment required to replace your torque converter.
Note: The information below is intended for general informational purposes solely to help give you an idea of project difficulty and tools required. As all cars are engineered differently, repair procedures and safety hazards vary from vehicle to vehicle. To ensure that you have a vehicle specific repair procedure and an exhaustive list of potential safety hazards, we advise you reference a factory service manual for your vehicle. Similarly, referencing a repair manual such as Chilton or Haynes might serve as a less expensive alternative.
Minimum Tools Required
• A code reader/scanner to clear trouble codes that arise when the battery and electrical connectors are disconnected; note that on some vehicles, a dozen or more codes may appear when you remove battery power from the ECU
• A comprehensive professional mechanic’s tool set that includes sockets and ratchets
• An engine hoist if your vehicle requires the removal of the engine and transmission as an assembly
• If you plan to leave your engine in during the repair, a transmission jack will be helpful
• A floor jack and at least four properly rated jack stands to lift and support the vehicle
• An adequate supply of automatic transmission fluid of the correct type, grade, and formulation
• You will need to torque everything to spec using a properly calibrated torque wrench
A Few Tips
If you have chosen to undertake a torque converter replacement, the following are some practical tips to potentially save you some time and trouble during the process:
• Before you remove anything, take as many close-up pictures as you can of vacuum line and wiring routing for reference purposes; this will save you hours of trouble later since you won’t have to figure out which wire or vacuum line goes where.
• Place all fasteners in separate, and clearly labelled containers as you remove them; for instance, place all suspension bolts in one container, all engine bolts/screws in another, and all others in another. This way, you will know which bolts go where when you reassemble the vehicle. You may find a magnetic tray helpful here to keep your fasteners in one spot while you work.
• If you have to remove the drive shafts on a FWD vehicle, drain the transmission fluid into a suitable container before you pull the shafts from the transmission to prevent a major fluid spill later on.
• Torque each fastener to its recommended torque value as you insert it upon reassembly as the best way to ensure than no fasteners remain un-torqued.
• Since you are going to be in there already, this is also a great time to consider replacing your transmission filter.
Best Torque Converter Brands
When it comes to choosing the best torque converter out there, there are tons of options. To help make your search a little easier, we have provided our recommendations below for the best torque converter brands.
TCI torque converters are manufactured using specialized welding and balancing techniques to ensure reliable and efficient operation for both street use and competition applications. TCI also remanufactures used torque converters either to original OEM specs, or to custom specs for high-torque applications. Moreover, TCI offers a 30-day warranty on competition-grade torque converters, and a 90-day warranty on torque converters used in street and strip/drag racing applications. Overall, they are good quality and we are confident that they will serve you well.
Although B&M offers torque converters for street use, the company focuses on torque converters for muscle cars and custom builds that require higher stall speeds. The performance-oriented torque converters supplied by B&M are typically fitted with needle roller thrust bearings instead of thrust washers to improve both durability and torque transfer. Overall, B&M makes a great torque converter that is likely to withstand the test of time for even the drivers with the heaviest right feet.