There are two different differential cases on the W126 cars.

The 5 & 6 cylinder cars use use a 1 liter capacity case, the V-8 cars use a 1.3.

Not sure what was used on the 380SE, but the diff for your car was used on the W116 and R107 chassis as well.

I think the lowest (numeric) ratio is 3.07 found in the 450 series of both the W116 and R107. Late V-8s used a 2.47 diff.

Ratios down to 3.69 can be found in the 1 liter case, generally used for the M110 engined cars, but this diff may not be robust enough for even a M116's torque....

Jim

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14 E250 BlueTEC black. 45k miles
95 E320 Cabriolet Emerald green 66k miles
94 E320 Cabriolet Emerald green 152k miles
85 300TD 4 spd man, euro bumpers and lights, 15" Pentas dark blue 274k miles