Testing Transmission During Test Drive

Testing During Test Drive


Notes:

The test procedures described are used to check the normal functions of the automatic transmission. Assessing operation and possible faults of the transmission naturally demands experience in the use of automatic transmissions. Should this not be available, it is good practice to make use of another automatic transmission of similar design and in proper working order as a comparison. If the test reveals irregularities, the cause for the fault detected can be found with the aid of the "Programmed Repairs".

Before starting the test, always check the oil level in the transmission, idle speed of the engine and setting of the control pressure cable.

Test Drive

During the test drive, it is necessary to check not only the shift points but, particularly, the transitions during a gearshift.

Upshifts at partial throttle should proceed in such a way that they can only be felt by concentrating on them. At full throttle and kickdown, the gear changes should be clearly felt, at the same time, however, the new gear should engage smoothly and the impression of the power of the engine must be retained. For example, if the engine revs up suddenly when the transmission shifts up, this indicates that a servo element is slipping (brake band or clutch) and this must be examined more closely.

Automatic downshifts without throttle are performed at very low speeds and can only be felt by concentrating (increase in engine speed). By contrast, a downshift at kickdown involves not only an increase in engine speed but a perceptible gearshift. At certain speed ranges, it is possible to perform a downshift at partial to full throttle.

Downshifts with the selector lever are either downshifts with the throttle depressed (e.g. on a hill) or braking downshifts without use of the throttle (e.g. on a downhill stretch or for slowing down). Downshifts with the throttle depressed need only a few fractions of a second for the gearshift whereas braking shifts without the use of the throttle require times of 1 to 2 seconds.

During the test, ensure that the transmission is not constantly shifted, particularly under load. During the gearshift, a lot of heat is developed at the servo elements. A reference value in this connection is:

Do not repeat a shift under load more than once within 15 seconds.