Your torque converter is essentially a hydraulic pump that acts as the link between the engine and the transmission. Various components within the torque converter use vanes, similar to a turbine, to act on the transmission fluid within the unit to create a fluid coupling, as well as provide the fluid pressure that the transmission needs. Failures within the torque converter can cause symptoms similar to a failing transmission, so include it in a diagnosis of suspected transmission problems. If you have a transmission failure that released metal salt and friction-material particulates, then you should replace the torque converter as well because you can’t fully flush out the debris. A torque converter is a sealed unit, and as such must be serviced or replaced as a unit. The unit is encased in a shell made of two halves that are welded together. Failures of the welds in the outer or inner joint will cause a fluid leak.
Your torque converter can make a variety of noises when it goes bad. You may first notice a whine, similar to a power-steering pump that is low on fluid. The stator within the assembly uses an overrun mechanism with a series of clutches that, when bad, can cause a rattling noise. The noise may be light while idling in park, but when you put the transmission in gear, the sound will increase in volume and frequency, and that is the death knell of your converter.
Slippage and Weak Acceleration
As the output pressure from the torque converter drops, the transmission will be starved and start to slip. This may manifest itself as a general loss of power when driving, especially when accelerating. Address this as soon as possible to prevent prematurely wearing out the friction material in the transmission. Slippage can also occur if the converter clutch fails to engage fully, leaving only the fluid-coupling effect, which is inherently inefficient.
Another symptom of lowered pressure output from the converter is a tendency to have soft, or delayed shifts. You will lose the nice, crisp feeling of the transmission shifting and engaging properly. You may find that increasing the output pressure from the converter by raising the engine rpm a bit will help the transmission shift into gear, and also to engage when starting from a stop.
Inconsistent output from the torque converter can cause the transmission to increase and decrease the vehicle speed with no concurrent change in throttle as the hydraulic pressure varies. This can present a dangerous driving condition, and you shouldn’t drive the vehicle until repairs are performed. Sometimes this variation can feel like a shudder, though you should inspect the transmission mounts and repair or tighten them as necessary before looking to the torque converter.
Transmission Adaptive Functions (5L40-E/5L50-E)
The Hydra-Matic 5L40-E/5L50-E uses a line pressure control system that has the ability to adapt the system line pressure in order to compensate for normal wear of clutch fiber plates, seals, springs, etc. The adapt feature is similar in function to fuel control (integrator/block learn).
The Hydra-Matic 5L40-E/5L50-E transmission uses the adapt function for garage shifts, upshifts, and TCC applications. The transmission control module (TCM) monitors the input shaft speed in order to determine if the shift is occurring too fast or too slow and adjusts the pressure control solenoid in order to maintain the correct shift feel.
Shift Adapt Relearn Procedure
Perform the transmission adaptive learn procedure after any of the following service procedures:
- Transmission replacement or a major overhaul
- TCM replacement or reflash
- Valve body replacement
Coast Downshift Adapt Procedure
After certain repairs, the adaptive values have to be erased. These cells then need to be refilled to get an optimal shift quality. However, only coast downshifts will require special care described in the following steps:
- Drive the vehicle in Drive to obtain normal transmission operating temperature.
- Travel 73 km/h then lightly brake to a stop, taking about 13 seconds.
- Travel 73 km/h then moderately brake to a stop, taking about 6 seconds.
- Travel 40 km/h then coast to about 8 km/h.
Repeat the above steps 3 times each.
Please follow this diagnostic or repair process thoroughly and complete each step. If the condition exhibited is resolved without completing every step, the remaining steps do not need to be performed.
An alternative way to reset Transmission Adaptive Pressures is by using a Tech 2 or Vident scan tool with the GMH software loaded.
Failed Torque Converter with Healthy Transmission
The community has seen many cases where the torque converter has started to fail and a swap early enough has saved the transmission, if you can catch a failing torque converter before it internally disintegrates then sending foreign contaminants through the fluid back into the transmission a lot of the times you could spend $400 on a reconditioned torque converter and then swap them over and have a totally fine transmission or many hundred thousands of kilometers. In our V6 Adventra’s we have now swapped 3 converters and they are still going strong, our first symptom was bouncing RPMs at cruise speeds outside of the torque lockup range and now they are continuing to drive on in a healthy fashion.
If you wait till it’s too late expect to spend from $3,000 to $5,000 for a total rebuild.