I changed over to a lower gear ratio in order to quiet the car down on the highway. With the 3.07 factory ratio, the car was "busy" at highway speeds. The 2.47 lowered the rpm's by about 700 at cruising speed. Made me very happy. That said--your 1980 SD is a 116 chassis and probably(?) uses a different rear end than the 126 SD. I got mine from a 420SEL.

Tom

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1993 300TE
1984 300D
1984 300SD
1976 BMW R90S