I just bought a 1982 (Model Year) 300TD with 360,000Mi. The Engine and trans. were traded from a 1982 300SD with 140,000Mi. The owner did not set up the speedometer cable because he said there were mechanical/electronic differences between the TD/SD trans. Any tips on how I can fix this before I loose track of my milage or get a speeding ticket :?:

I would check with your local dealer. I believe the TD is geared lower than the SD. Keep us posted on what your dealer says.

Ken

Would there be a length difference between the speedo cable the SD and TD use?

I have found out that the transmission is actually an SD trans with an electronic speed sensor. Where can I convert my mechanical speedo to electronic?

My recommendation would be to replace the speedo and odometer with an electronic one. On a budget, look for a used one at a salvage yard.

If you find one that the odometer does not seem to work, fear not. It is probably a problem with a slipping pot metal gear on the odometer drum shaft.

Speedometer accuracy will be dependant on wheel diameter and rear end differential ratios also.

Would a gauge from a salvage SD be straight "swappable"? Would I need shielded wires between the gauge and the trans?

My wiring diagram shows a direct conductor (wire) from the #1 connecting pin at the transmission to the #5 connecting pin on the back of the instrument cluster containing the speedometer. The conductor is a 0.75 mm diameter wire (white).