Jumpy speedometer needle
 

When starting out, the speedo needle in my '85 300D is jumpy between 0 and about 20 MPH. At higher speeds it seems to flutter a little. Is this a cable problem or is the speedo head in need of lubing?

Probably a cable problem. They tend to bind more at lower speeds and smooth out a bit as you speed up. Try pulling your instrument panel and pulling the inner speedo cable out. Wipe it clean and then reinsert it as you squirt some graphite on it (don't use oil). the inner cable should slide right back in if you twist it a bit as you reinsert it. If the cable is in good shape that should solve your problem.

Both of my TDs' speedometers do the same thing. I'll have to try the lubing idea.

I've replaced speedo cables on other cars that I've had and I always gave them a good coat of grease plus I would inject some grease into the cable housing. Would that be a good idea on a M-B?

Grease and oil tend to collect dirt (although in a speedo cable I think it's actually worn metal filings) and stiffen up over time. Graphite won't do that and the irregular surfaces inside the cable tend to hold the graphite in place pretty well. A local speedo shop I have used also strongly seconded the graphite only philosophy.

When you pull your inner cable out look at it closely to see if it shows signs of wear. If so, and the wear is minor, you should be able to just replace the inner. If the inner cable has started to unravel (unlikely if it's still working decently) then you'll need to replace the whole cable. If the inner cable looks good just clean it up and relube with graphite.

This assumes of course that you haven't inadvertantly kinked the cable somehow doing some other repair. If that's the case you may be able to straighten it. If not it's time for a new cable (the whole thing).