1985 300sd speedometer swap
 

Hello all. I have a 1985 300sd and I want to replace my mph speedometer with a km speedometer. Can it just be swapped out with any W126 unit? Thanks.

Mike

Not exactly, it has to be matched to the differential gearing. IIRC, the 300SD was only sold U.S.

I've been doing some research on this and I believe the differences are on the interface board which the electrical connection is made and then to the "mechanical" portion.

Having changed the differential on mine, I need to find out the component differences between a 420SEL and 300SD interface board.

I think 126 300SDs were also sold in Canada.

One option might be to replace the speedo mph faceplate with a km/h faceplate. Any 126 faceplate with the same range should work. You might be able to customize a 123 or 201 faceplate with the same range.

Edit - the odometer will still be in miles.

Sixto
98 E320s sedan and wagon

Your speedo is specific to your differential (2.88) which was a one year only (1985) so you need a speedo out of another 1985 model.

There probably is a very simple fix for this. It's likely to only be a couple of components on the circuit board that change this and if you could take a good detail photo of the circuit board, we likely can come up with something. Maybe James Dean has some information.

2nd Gen w126 1986-87 300SDL had 2.88 also.


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Sorry, I was referring to w123's with mechanical speedo.