How can torque converters fail?

Question

In what ways can a torque converter stop working properly?

Are there any symptoms that indicate failure, or simple tests one could do to determine a malfunctioning TC?

Answer 1

A torque converter (TC) can fail in several different situations:

• Since TCs are made of metal, they are welded together. These welds can fail (split or break) due to excess pressure or by a poor welding job. This is most easily noticed leaking transmission fluid.
• Internally, depending on how the pump, stator, or turbine blades are affixed, these too may become loose or disconnected from their home. This usually results in catastrophic failure of both the TC and the transmission as bits/pieces of metal go through.
• The stator clutch (or sprague unit) can fail. If the stator is allowed to turn in either direction, the TC will lose its ability to allow the TC to torque multiply. When this failure occurs, it will feel like the vehicle is very sluggish from take off.
• Some TCs have a lock-up mechanism. When a vehicle gets up to speed, the pump and turbine start spinning at almost the same speed. The lock-up mechanism will cause these two parts to spin as one, which increases efficiencies by doing so. This type of failure is usually noticed by a wobble (out of balance feeling ... like a tire being out of balance) when it is trying to engage. It will continue to wobble, but pulling your foot off the accelerator for a brief second, then back on will usually allow it to lock up and the wobble will go away.
• In performance applications, if pressures and heat are high enough, the outer shell can actually bulge outward. This would be hard to detect without seeing the TC direction, but performance would suffer much like if the stator clutch had failed.

Answer 2

This video illustrates how a torque converter can lock up and shows the actual part that locks up...