Stall test procedure

1 Drive car or run engine until engine and transmission has attained normal working temperatures.

2 Check the level of fluid in the transmission box and correct if necessary.

3 Apply the hand brake and chock the wheels.

4 Connect a tachometer via leads to the coil ignition terminals.

5 Apply the foot brake, select D range and fully press the accelerator pedal down for a period not exceeding 10 seconds to avoid overheating the transmission fluid (this is very important).

6 Quickly observe the highest engine speed reached on the tachometer and immediately release the throttle pedal.

7 Shift selector lever to N and allow transmission fluid to cool at least two minutes or more before commencing next test.

Interpreting stall test results A typical stall test maximum engine speed could be 2300 rev/min ±100. If the actual stall speed differs from the recommended value (i.e. 2300 rev/min), Table 5.3 should be used as a guide to trace the fault. The stall test therefore helps to determine if the fault is due to the engine, the converter or the transmission assembly.

Note The reason why a slipping torque converter stator drags down the engine's maximum speed is because the spinning stator makes the converter behave as a fluid coupling (no torque multiplication), causing the fluid to have a retarding effect on the impeller.

By performing the stall test in D, '1' and R range, observing in which range or ranges the slippage occurs and comparing which clutch or band operates in the slipping range enables the effective components to be eliminated and the defective components to be identified (see Table 5.4).

Table 5.3 Table of stall tests

Test results Possible causes

Below 1600 rev/min Stator slip

Approximately 2100 rev/min Poor engine performance

Above 2500 rev/min Transmission slip

Examples a) Slip in R can be the drive and reverse clutch or first and reverse brake. Engage '1' range. If slip still occurs, first and reverse brake must be slipping.

b) Slip in D can be forward clutch or one way clutch. Engage '1'. If slip still occurs, forward clutch must be slipping.

c) Slip in R can be the drive and reverse clutch or first and reverse brake. Engage '1' range. If there is no slip the drive and reverse clutch could be slipping.

Road test for defective torque converter A road test enables a seized or slipping stator to be engaged, whereas the stall test can only indicate a possible slipping stator. The symptoms for a faulty stator one way clutch are shown in Table 5.5.

If the converter one way clutch has seized, the vehicle will have poor high speed performance because the stator reaction above the coupling point speed hinders the circulation of fluid if it is not able to freewheel. Conversely, if the converter one way clutch is slipping there will be no stator reaction for the fluid and therefore no torque multiplication so that the acceleration will be sluggish up to about 50 km/h.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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