1.Fluid should be at Operating temperature:
Take the MB for a 20 minute drive...at least 25 miles.
(AND not 85 + MPH on an interstate,
If so you'd have to let the engine/tranny idle for about 5 minutes to cool off.)
2.Park on completely LEVEL pad.
(If the Chassis is not level you're wasting your time.)
[ I use a 4 foot level if in an unknown area.]
2a. Just before you check the fluid level run the gearshift lever back and forth
through all the gears (With foot on Brake pedal) allowing engagement of ALL the gears.
3. Pull the Dipstick and wipe it with a "LEATHER" cloth. (Per FSM)
ANY other Cloth can leave residue ("Strings") that can clog the TINY
Passages in the Valve body.
PAPER TOWELS are the second big "NO NO".
4. Re-Insert the Dipstick and check the fluid level.

Changing ALL the Tranny Fluid (Both in the Pan AND the Torque Converter)
And installing a New Transmission fluid filter are default "First Steps" for any
irregularities in tranny performance.

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'84 300SD sold
124.128