As mentioned before the SD's speedo/odo are drive by electronics and have plastic gears for the odometer. I've done a fair amount of work on these and if you're interested would be happy to go through yours and fix it up.

Here are some photos from an 81 I worked on. He was having problems with his odometer not keeping proper mileage. Was an interesting repair. He was also interested in adapting a 160 MPH speedometer for use in his SD. I ran out of time on the project and didn't get a chance to fully figure out the needed changes.

W126 300SD (1981) Instrument Cluster Refresh RT - Album on Imgur

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k