The book I have indicates a 3.46 rear gear ratio for a 300D. My calculations indicate 3,266 RPM at 70MPH with 185/75 14 tires. You probably have a 195 or 205 which would work out a little slower engine speed. 3.100 seems about right.

The 240D engine really screams, it has a 3.69 gear. I would really like to have a five speed with an overdrive fifth. I can always dream I guess.

Good luck,

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Larry Bible
'84 Euro 240D, 516K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in
Mercedes automobiles