What Does a Bad Torque Converter Sound Like?

Converter Basics

A torque converter is a fluid coupling, meaning that it uses fluid to transfer power from one place to another. The outer case of the torque converter bolts to the engine, and fins welded to the inside of the case circulate fluid when the case spins. A separate set of fins inside the case connects to the transmission input shaft. At low rpm, the engine-driven fluid simply slips through the transmission-side turbine blades. At higher rpm, the transmission turbine can no longer pass fluid without moving. A lock-up clutch inside the converter locks the engine to the transmission under cruise.

Whirring on start-up is usually the first sign of torque converter failure, and it happens for one or all of three reasons. The torque converter contains several bearings and at least one one-way clutch; those bearings or clutches may emit a faint to pronounced whine when worn. The next two reasons have to do with the nature of moving gas in a fluid. When a pump tries to force air through a fluid, the air breaks up into tiny bubbles, which collide, pop and emit a faint vibration that vibrates the converter housing and manifests as whine. A malfunctioning transmission-side turbine will force fluid to continue to circulate through the engine-side impeller, where it will cavitate (develop vacuum bubbles) and emit a whine.

Failure to transfer fluid pressure almost always precedes complete converter failure. When the engine-side turbine can no longer transfer power to the transmission input turbine, the engine will rev without engaging the transmission. This will generally start out as a slight increase in stall speed (the rpm that the engine gets to before engaging the transmission), and will progress to slippage while shifting. Eventually, the torque converter will either completely fail to engage the transmission, or it will engage it sporadically and shudder. This is especially true of transmissions with lock-up converters, where the lock-up clutch may quickly engage and release before locking in or giving up completely.

Just before a converter completely self-destructs, it'll emit a loud grinding or clacking noise that sounds something like dragging a steel refrigerator down the road at 70 mph. Depending upon what's actually broken in the converter, this grinding may increase or decrease in pitch with with rpm. Once you hear your converter's death rattle, what's actually broken inside of it is fairly academic: The converter is hashed, and continuing to drive it that way will almost certainly send shrapnel through your transmission and destroy it (assuming the converter will still transfer power at all, which is unlikely).