Checking Transmission Operation

Prior to making repairs on an automatic trans- B - Transmission Fluid Level mission, troubleshoot transmission as instructed below and with help from the following tests.

A - General Checks

B - Transmission Fluid Level

C - Stall Test

D - Test Drive

E - Pressure Test

The specified fluid level is extremely important for proper operation of automatic transmission, so that following test must be carried out with great care.

Checking A TF Level

Important

All jobs, which require that engine runs, should only be carried out with selector lever in "N" or "P" and parking brake applied.

Exceptions: Tests, which require briefly a different selector lever position.

Also check appearance and odor of ATP. Burnt friction linings cause a burnt odor. Contaminated oil could cause failure in valve body.

In this case transmission must be removed and repaired or replaced.

Test is carried out at engine idle speed, parking General Checks brake applied and selector lever at "N". Car must he on level surface.

Following jobs must be performed prior to any testing of transmission, and if defects are found, they must be eliminated before continuing with other work on transmission.

1. Check engine tuning (ignition timing, idle and transition).

Let engine run at idle speed 1 to 2 minutes before checking fluid level, so that torque converter will be full.

2. Check for external damage, e. g. leaks on ATF level can be checked on a cold or warm transmission (ATF) or final drive (hypoid oil) transmission. However, the level will be more and missing or loose mounting bolts. accurate on a cold transmission (20° - 30°C/

68° - 86° F ATF temperature). An ATF temperature of 80 C/176 F can only be guesstimated.

ATF level in transmission will change with fluid temperature. Max, and min, marks on transparent tank are in reference to an ATF temperature of 80° C/176° F. When ATF temperature is 20 to 30° C/68 - 86° F, the ATF level will be 30 mm/ 1 3/16 in, below minimum mark {see figure). The amount of ATF between min, and max, marks is 0. 2 liters/6, 75 fluid ounces.

After correcting ATF level to specifications, operate brake pedal, leave selector lever in each position (R-N-D-N-R) several seconds and then return it to "N", so that working pistons of power parts are filled with ATF. Recheck and, if necessary, correct ATF level.

Special Tool Sporsche 928

C - Stall Speed

This check provides information on operation of engine, converter and transmission. It is applied, when top speed cannot be reached or acceleration is insufficient.

Note

During this check all the engine power is converted into heat in the converter, which is why this check must not last longer than 5 seconds.

Rear wheels must not be permitted to turn for this check.

Also engine must be at operating temperature and develop its full power.

temperature

Add ATF to correct level. Cleanliness is essential!

If ATF level is too low, oil pump will draw in air, which can be heard. ATF will foam and cause incorrect readings when checking ATF level. Stop engine until ATF foam disappears (approx. 2 minutes). Add ATF and recheck ATF level.

Excessive ATF must be drained or drawn off, since otherwise transmission components would splash excessively and raise the temperature too much, until finally foamed oil is forced out through vent. This condition could damage transmission on a longterm basis.

Extra equipment, e. g. compressor for air conditioning, tnusi be turned off.

Check must not be made with car's tachometer.

1. Connect tachometer that it can be read from driver's seat.

2. Run engine at about 2000 rpm approx. 2 minutes prior to testing.

3. Apply parking brake all the way and depress brake pedal with left foot.

4. Position selector lever at "D", floor accelerator pedal with right foot and check whether specified stall speed is reached.

Stall speed must be 2400 - 200 rpm. Note

If stall speed drops by approx. 400 to 700 rpm below specified value, one-way clutch in torque converter is slipping.

If stall speed is faster than specified value by about 300 rpm, slip is in transmission.

If stall speed is correct and lop speed is still not reached, one-way clutch is locking in both directions or has seized. This will usually be noticed during fast highway driving by ATF leaking through the vent.

The stall speed will drop by approx. 125 rpm for each 1000 meters/3900 feet altitude above sea level because of a drop in engine power.

Even excessively high outside temperatures could cause stall speed to drop slightly below the minimum value.

Vehicle should be driven in all gear ranges and under ail possible road conditions. Do not test drive if there is obvious mechanical damage.

Shift points in km/h (mph)

Selector lever position "D"

Upshift

Downshift

Accelerator pedal position

km/h (mph)

km/h (mph)

Pari throttle 1-2-1 2-3-2

26 - 33 (16 - 21) 42 - 48 (26 - 30)

16 - 23 (10 - 14) 32 - 37 (20 - 23)

Full throttle 1-2-1 2-3-2

97 - 105 (60 - 65) 150 - 158 (93 - 98)

45 - 52 (28 - 32) 57 - 85 (35 - 53)

Kickdown 1-2-1 2-3-2

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