General shift mechanism problems
1. This deals with checking and adjusting the shift linkage on
automatic transmissions. Common problems which may be attributed to poorly adjusted linkage are:

A) Engine starting in gears other than Park or Neutral
B) Indicator on shifter pointing to a gear other than the one actually being selected.
C) Vehicle moves when in Park.

Transmission won't downshift with gas pedal pressed to floor
1. There are many probable causes for the above problems, but the home mechanic should be concerned with only one possibility - fluid level.
2. Before taking the vehicle to a repair shop, check the level and condition of the fluid. Correct fluid level as necessary or change the fluid and filter if needed. If the problem persists, have a professional diagnose the probable cause.
3. If the transmission shifts late and the shifts are harsh, suspect a faulty vacuum diaphragm.

Fluid Leakage
1. Automatic transmission fluid is a deep red color. Fluid leaks should not be confused with engine oil, which can easily be blown by airflow to the transmission.
2. To pinpoint a leak, first remove all built-up dirt and grime from around the transmission. Degreasing agents and/or steam cleaning will achieve this. With the underside clean, drive the vehicle at Low speeds so air flow will not blow the leak far from its source. Raise the vehicle and determine where the leak is coming from. Common areas of leakage are:
A) Pan: Tighten the mounting bolts and/or replace the pan gasket as necessary.
B) Filler pipe: Replace the rubber seal where the pipe enters the transmission case.
C) Transmission oil lines: Tighten the connectors where the lines enter the transmission case and/or replace the lines.
D) Vent pipe: Transmission overfilled and/or water in fluid.
E) Speedometer connector: Replace the O-ring where the speedometer cable enters the transmission case.

Note: If you added extended breather tubes on your transmission, make sure there aren't any sags in the tube.  A droop or sag in the tube can allow fluid to collect and block the vent tube.  This can cause the fluid to be forced out of the transmission.  This can even cause the fluid to be forced out through the filler tube.