Draining a GM automatic transmission on video,
be careful, the video does not indicate purging the box (by shifting through all the gears successively):

Draining procedure step by step:

1) Run the car to obtain the operating temperature of the box

2) Place the car horizontally on a bridge, driving roads hanging

3) Put position P (parking)

4) Stop the engine

5) Open the drain screw and collect the oil in a container allowing you to know approximately the quantity drained

6) Dismantle the oil pan gradually in a crisscross fashion to avoid deformation

7) Remove the oil filter

8) Install the new filter

9) Clean the housing and the magnet never use a lint or paper cloth
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