My 1980 SL speedometer only goes to 85mph. What would it take to
>convert this to a 160mph speedo? Is the gearing different just in the
>speedo head or would there be more th The 1980 US 450SL has a rear axle ratio of 2.65:1, which is unique to the 107 series SL line. It is a one year only ratio, changing from the earlier 3.07:1, and in 1979 3.06:1 ratio. The 380 and 560SL's have
2:47:1 ratios, so that is also not an exact fit. I'm pretty sure that
116 chassis speedo's interchange, but I could not find any ratios that are any closer as the rear end ratios in the US changed at the same time, and they too had the 85 mph speedo markings.
Going one way, you'll be off 15%, and the other, about 7%. The only other way to do it is to have the speedo face recalibrated and screened by a VDO repair center.