To tell whether the transmission or the torque converter is bad, look at when the problem happens. Torque converter problems show up as shudder at light throttle around 30 to 50 mph, lockup not engaging, slipping that feels like the engine revs without pulling from a stop, and overheating. Transmission problems show up as harsh, late or missing shifts, slipping between specific gears, delayed engagement and gear ratio codes. Because a failing converter can send debris through the transmission, they are often replaced together.
Torque converter or transmission?
| Symptom | Points more to |
|---|---|
| Shudder like driving over rumble strips at steady speed | Torque converter clutch; see torque converter shudder |
| Higher cruise rpm, no lockup, lockup codes | Converter or its lockup control; see torque converter lockup |
| Engine revs but the vehicle is slow to move from a stop | Converter stator or a slipping transmission |
| Harsh, late or missing shifts | Transmission valve body, solenoids or clutches; see valve body problems |
| Slipping on one particular shift | Transmission clutch pack for that gear |
| Whine that changes with engine speed in neutral | Pump or converter; see transmission noise |
Tests that help
- Read codes; lockup codes such as P0741 point to the converter circuit, while ratio codes point to the transmission.
- Check the fluid level, color and smell; see transmission fluid color.
- Note whether shudder disappears when you press the brake lightly at cruise, which releases lockup.
- A shop can perform a stall test and line pressure test to separate the two.
Can you replace just the torque converter?
Yes, if the transmission itself is healthy: clean fluid, no debris in the pan and good shifts. The transmission must come out to reach the converter, so labor is similar to a transmission swap. If there is metal in the pan or the transmission already slips, replacing only the converter rarely solves the problem.
Why they are often replaced together
A converter that is breaking up sends metal and friction material into the transmission and cooler, and a failed transmission contaminates the converter. Most transmission rebuilders replace or rebuild the converter as part of the job, and the cooler and lines must be flushed. See bad torque converter symptoms and transmission rebuild.
Fluid tells a lot
Dark, burnt fluid with clutch material points to the transmission’s clutches; glittery metal can come from either the converter or the transmission’s gears and bushings. Clean, red fluid with a lockup shudder points more to the converter clutch or the fluid’s friction properties.
Replacing the transmission
Most replacement automatic transmissions are sold with a torque converter; check the listing. See how to install a transmission, transmission replacement cost and our transmissions.
More guides: rebuilt vs used transmission · transmission mount symptoms · torque converter replacement · how long a torque converter lasts.
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