I am looking at a couple of speedometer replacements for my 1984 300D. My part # is 123 542 28 57, and the travel is 0-120(125 with last dash)
I am looking at a #123 542 37 01, with a travel of 0-150 MPH, and #123 542 25 01, travel of 0-110(115 including last dash)
Will these guages work on my car? Either one is cheaper than a rebuild and one is brand new

Thanks

I think you have to look at the shift points on the dial (the little hash marks that indicate the top of each gear range). If they're identical, the speedos will be usable. If not, the speedo won't be accurate at all.

The speedometers are designed for different rear-end ratios.

The other difference is in the pick-up for the cruise control--they're different on different models.

In general, the different speedos are not interchangeable, but you might luck out.