Stall Speed Test

This test is used to check for faults in the torque converter and planetary gear system when there is no other apparent cause for poor performance and acceleration. The test results are meaningless if the engine is not running properly. A precise tachometer must be used for the rpm measurements, as dashboard instruments are not sufficiently accurate.

To test:

1.	Drive the vehicle to warm the engine and transmission to normal operating temperature.

2.	Connect a tachometer according to the instrument manufacturer's instructions, so that it can be read from the driver's seat, then start the engine.

3.	Set the parking brake and depress the foot brake firmly to hold the vehicle stationary.

4.	Place the selector lever in D.

5.

While holding the car stationary with the brakes, floor the accelerator for no more than 20 seconds. Notice the tachometer readings. The rpm should increase, and then hold steady. For transmission code TJ the rpm should be between 2200 and 2500. For transmission code TL, between 2210 and 2460. For transmission code TNA and TN, between 2320 and 2570. Maximum rpm achieved under these conditions is the stall speed.

A stall speed that is a few hundred rpm below the specified range is probably due to reduced engine performance. A stall speed that is 400 rpm or more below the specified range indicates a faulty torque converter.

If the stall speed is above the specified range, there is slippage in the forward clutch or in the 1st gear one-way clutch. To determine which is faulty, repeat the test, this time with the selector lever in 1. If the stall speed is now within specifications, then the 1st gear one-way clutch is defective. If the stall speed rpm is still high, then the forward clutch is defective.

The test can also be made with the selector lever in R. If the stall speed is too high, it indicates slippage in either the direct/reverse clutch or in the 1st/reverse clutch.