The odometer fails because a press fit pot metal gear loses its grip on the shaft. A small amount of dirt or expansion of the metal can help it regain its grip. The real test comes when it has to turn all the digits at one time.

The above is from a previous post.

My 84 300 CD is 500 miles short of 300,000 (and has been for the last week or so when I finally realized that it wasn't getting any closer). Assuming this is the problem, since the speedo works fine and the 299 numbers are half turned, how easy is the fix from a time perspective? If its a real pain, I'll just leave it and change my oil every 5 weeks instead, which historically usually corresponds to 3000 miles.

Thanks

MikeL

That's my post. It's about a twenty minute fix once you remove the instrument cluster which should also take about 20 minutes. The fix is simply to bugger up the shaft with something so the press fit is tight again. Some people suggest a punch, I just used a vice grip. The directions to repair it are found in a thread somewhere on this site and are very good. You will need to push the shaft out, on which all the numbers turn, with a drill bit the same size as the shaft to hold everything in place while you work on the shaft.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

When I took mine apart to fix it, somene had already center-punched around the bore of the gear in an attempt to prolong its life. I found I could drill and tap the gear for a 4-40 set screw to hold it securely to the shaft.( it helps to have access to a milling machine to do this)

A small amout of red LockTite (the removable stuff) also works fine. I've not tried it on a W123, where the drive gear is on the other end, but it works fine on a W108 or W115 (I've fixed both).

If you can move the odometer drive shaft back and forth a bit, just put some LockTite on a toothpick and coax it down the the shaft/gear interface, then work the shaft back and forth to get some in there. Should lock up in a few seconds (locktite is an anaerobic setting glue, it won't set in the presence of oxygen). Wipe off any that isn't at the gear/shaft interface with some paper or similar, especially around the hole where the shaft goes through.

Easier than pulling the shaft.

You can also go whole hog and get a replacement gear from a speedo place, or send it out for repair. I know Palo Alto Speedometer does them, so do several others. Costs about $100.

If you do remove the shaft, be VERY carefull to keep the numbers aligned -- if you don't, not only is the odo incorrect, but you can get the wheels off a bit, so that the numbers don't align properly as the count up.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

The fix I used on my 280SE was after removing the speedometer, I used a tiny drill bit (.032", approx.), drilled thru the shoulder on the gear, thru the shaft and inserted a short piece of .032" safety wire thru the hole. Bent the wire so as not to interfer with anything, works great! The other fixes mentioned in this thread, I didn't think of or didn't want to tap on the shaft. YMMV
Thanks

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Jerry -
If you don't learn something new every day, you aren't paying attention!!
1971 108 280SE 2.8 "Ronnie"
1985 300TDT (76,904 Original miles ) "Sadie" (Sold-went back to Arkansas)
1984 300DT "Green-go" (Sold)
1984 300DT "Silver Bullet" (Sold)
1956 220S Ponton
1985 300D (Sold)
1984 300D