I wantt o swap out my 3.58 diff to a 3.09. I feel like im burning up the motor at 70MPH even though im sure its fine. A 3.09 diff would lower the engine speed by about 600 RPM.

So will I have tyo swap out my speedometer for one that works with a 3.09 or can it be adjusted to read properly?

Thanks

__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

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