21-12-2012, 12:44 PM
Automatic Transmission Stall Test
Automatic Transmission.ppt (Size: 1,010.5 KB / Downloads: 78)
Purpose
A Stall test is used to confirm transmission and torque converter problems by placing the maximum load on the transmission and torque converter.
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.
Preliminary Check, Fluid
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.
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.
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.
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.
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.
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.