Torque Converter Clutch Problems
Discover how a torque converter clutch works and how to diagnose common problems. When this system develops issues it can cause surging, bucking, poor fuel economy and intermittent stalling.
Why Do They Use a Torque Converter Clutch
One of the downsides of owning an automobile with an automatic transmission is there is no mechanical connection between the engine flywheel and the drive shaft. It does, however provide a fluid coupling through the torque converter. This is not as efficient as a manual transmission when it comes to fuel economy. In the early 1980s, when computer control modules started making their way onto automobiles, car makers found a way to overcome this inefficiency.
They installed an electronically controlled clutch that locks the torque converter shell to the flywheel in the same manner that a clutch would direct power from the engine through a manual transmission. When the converter clutch is applied it completes a 1 to 1 ratio with the engine crankshaft. This eliminates the power loss from a fluid coupling.
Torque Converter Clutch Operation
Car manufacturers needed to solve a few problems before they could deploy an automatic clutch locking system. First, they only wanted to lock up the transmission at Highway speeds over 40 mph. Second, when the clutch is engaged, engine power is reduced, so they needed the ability to release the clutch under acceleration or when the automobile slowed down to a stop. On the transmission side most manufacturers use a torque converter clutch solenoid. This electrically operated solenoid simply engages the clutch or releases it.
It’s the job of a control module to make the decision on when to energize or turned off the solenoid. Some of the important inputs that the computer uses to make this decision are as follows. They need to know the throttle position, engine load data from the manifold absolute pressure sensor, intake air density and speed from the mass air flow sensor, vehicle speed and input from the brake switch. With these pieces of information they can determine with a high degree of accuracy when the car would benefit from having the torque converter clutch applied and released.
Symptoms of Stuck Torque Converter Clutch
Since the torque converter clutch is either engaged or disengaged the symptoms fall into those two categories of malfunction. If the vehicle is slowing down for a stoplight and the clutch fails to disengage, the transmission will stall the engine when it stops. It’s the fluid coupling inside the torque converter that allows the engine to idle while the automobile isn’t moving.
When you remove this by locking it to the engine it acts like a manual transmission at stop signs. The symptoms feel like you were trying to stop at a traffic light without pushing in the clutch pedal on a stick shift car. In other words, you feel a violent surging and bucking as the vehicle slows from 5 mph and it will stall the engine when it reaches 0 mph.
What Happens When the Torque Converter Clutch Won’t Engage
If the solenoid fails to lock up the system at Highway speeds the driver will notice a few telltale signs. Normally when an automobile is driving at 55 mph the engine is loping along at around 1500 RPMs. When the clutch fails to engage at this speed the RPMs will be much higher. The other main symptom is poor fuel economy. On some automobiles this can be drastic. If the engine is running at a higher RPM at Highway speeds, gas consumption increases. Drivers can see a reduction of 5 to 10 miles per gallon with this type of torque converter clutch problem.
Torque Converter Clutch Repair
This is where a piece of good news enters the conversation. Although some of the symptoms can make it feel like there’s a horrible problem inside the transmission, diagnosis and repair of the issue are often a small fraction of the cost of other transmission problems. As an example, replacement of the torque converter clutch solenoid usually costs under $300. This is when they mount the part on the valve body of the transmission and removal or overhaul of the transmission is not necessary. Car owners can perform some DIY diagnosis by locating the TCC solenoid electrical connector and disconnect it to see if the symptoms of bucking, surging and stalling at stop signs disappear.