Automatic Transmission Stall Test Tom Birch

Purpose A Stall test is used to confirm transmission and torque converter problems by placing the maximum load on the transmission and torque converter. Tom Birch

Torque Converter Stall Torque converter stall should not be confused with a transmission stall test. Torque converter stall occurs when a locked torque converter causes the engine to stall. TC Stall can be caused by low fluid level, faulty torque converter controls or internal seals. Tom Birch

Preliminary Check, Fluid Minimum Maximum Before stall testing, always make sure the fluid is in good condition and at the correct level. The fluid level should be between the minimum and maximum points on the dipstick, and the fluid should appear relatively clean and have a reddish brown color. Tom Birch

Preliminary Check, Shift Linkage With your foot firmly on the brakes, move the shift lever through the gear positions. You should feel the transmission internal detents as the gear position indicator (arrow) or see the instrument panel display the gear range. Tom Birch

Stall Test Always use extreme caution when stall testing a vehicle. Firmly set the parking brake Firmly apply the brake pedal. Use wheel blocks on at least 2 wheels. Pressure Gauge Tachometer Tom Birch

Stall Test Cautions A stall test can: injure bystanders if the vehicle operator loses control. damage the vehicle if the vehicle operator loses control. overheat the transmission fluid if tested too long. burn out a clutch or band if it starts slipping. To prevent this, keep others away from the front or back of the vehicle. securely block the wheels and apply the brakes. limit tests to five seconds for each gear range. limit engine speed to a little above maximum stall speed. Tom Birch

rpm increase to stall speed Stall Test 2 A stall test is performed by: 1. Firmly applying the brakes 2. Shifting the transmission into gear. 3. Depressing the throttle completely (5 seconds maximum). 4. Watching the tachometer to determine the stall speed. 5. Releasing the throttle for idle. 6. Recording the stall speed. 7. Repeat the test for each of the gear ranges. rpm increase to stall speed Tom Birch

Stall Test 3 Note that the transmission is in Drive, the vehicle is going 0 mph, the throttle is fully depresses and the engine speed is stalled at 2,300 rpm. This tells us that the driving and reaction devices for D1 are working properly. Tom Birch

STC 2 When stall testing an electronic transmission, use caution if testing while the EPC solenoid is disconnected. The engine can possibly send enough torque to the transmission to cause damage. Tom Birch

Cool the fluid in the TC Many technicians will shift the transmission into neutral and increase the engine speed to about 1,500 rpm after each test period. This allows a fluid exchange in the torque converter and moves the hot fluid to the transmission cooler. Tom Birch

Interpreting the results Excessive engine speed during a stall test indicates slipping clutches in the transmission. A engine that is unable to reach stall speed lacks power or the torque converter one way clutch is slipping. Tom Birch

Interpreting the results The stall speed was high only in D1. This transmission has a slipping one-way clutch. The same driving member is used in M1 along with a second reaction member. Tom Birch

Interpreting the Results: High Stall Speed If all the stall speeds are higher than specifications, the problem is caused by a slipping apply device. Consult a clutch and band apply chart to determine which apply device(s) is effective in the gear range. Tom Birch

Interpreting the Results: Low Stall Speed If all the stall speeds are lower than specifications, the problem is caused by either: a faulty torque converter with a slipping one-way stator clutch. a weak engine. Tom Birch

Fluid Pressure Test Many technicians will attach a pressure gauge while making a stall test. It helps determine the cause of high stall speeds. Tom Birch

Air Test Shop air can be applied to these ports to operate the various hydraulic components. Excessive leakage or no operation indicate a transmission that needs repair. Tom Birch

AT 2 Some air nozzles use different tips that can seal openings or reach into ports that are hard to get to. Tom Birch