Torque Converter Stall Test

STALL TEST

Stall testing determines the maximum engine rpm obtainable at full throttle with the rear wheels locked and the transmission in Drive. Stall testing also checks the holding ability of the converter-stator overrunning clutch and both transmission clutches. When stall testing is completed, refer to the Stall Speed Specifications Chart and diagnosis guides.

WARNING: Never allow anyone to stand in front of the vehicle when performing a stall test. In addition, always block the front wheels and have the parking and service brakes fully applied during the test.

1. Connect the tachometer to the engine.

2. Check and adjust the transmission fluid level as necessary.

3. Start and operate the engine until the transmission fluid reaches operating temperature.

4. Block the front wheels.

5. Fully apply the parking brakes.

6. Fully apply the service brakes.

7. Open the throttle completely and record the maximum engine rpm registered on the tachometer.

CAUTION: Do not hold the throttle open any longer than necessary, and never longer than five seconds at a time. If more than one stall test is required, operate the engine at 1000 rpm with the transmission in Neutral for at least 20 seconds to cool the transmission fluid.

8. If the engine exceeds the maximum shown in the stall speed chart, release the accelerator immediately. This indicates that transmission clutch slippage is occurring.

9. Shift the transmission into Neutral, operate the engine for 20 seconds, stop the engine, shift the transmission into Park, and release the brake.

10. Compare the test results with the Stall Speed Chart and refer to the stall test diagnosis.

STALL TEST DIAGNOSIS

Stall Speed Too High

If the stall speed exceeds specifications by more than 200 rpm, transmission clutch slippage is indicated.

Stall Speed Too Low

Low stall speeds with a properly tuned engine indicate a torque converter stator clutch problem. The condition should be confirmed by road testing prior to converter replacement. If stall speeds are 250-350 rpm below the minimum specified in the chart, and the vehicle operates properly at highway speeds but has poor low speed acceleration, the stator overrunning clutch is slipping and the torque converter should be replaced.

Stall Speed Normal

If stall speeds are normal but road testing shows that an abnormally high throttle opening is required to maintain highway speeds even though low speed acceleration is normal, the stator overrunning clutch is seized and the torque converter must be replaced.

Noise

A whining or siren-like noise caused by fluid flow is normal during a stall test. Loud metallic noises from loose internal parts or interference within the assembly indicate a defective torque converter. To confirm that a noise is originating from within the converter, operate the vehicle at light throttle in Drive and Neutral on a hoist and listen for noise coming from the torque converter housing.

Stall Speed Specification Chart:

When the stall test is completed, compare the test speeds recorded with those listed in the Stall Speed Specifications Chart.