One of the guys at APT Instruments  //www.gaugeguys.com/contact.htm   told me that they can get the plastic gears, pawls that turn the gears and number barrels still from Smiths.  It must have been just expensive enough that I decided to try to fix it myself because I didn't pursue it.  Of course my fix didn't work.

A 45 year-old speedometer should be expected to have a few problems. They have problems turning all 5 wheels at the same time because the lubricant has dried out and become a bit gummy over the years. The same thing happens with clocks and watches. They are a fairly delicate mechanism so trying to modify the parts will usually wreck the odometer. The best fix you can do is to either shock the odometer into turning over or opening up the case and pushing the wheels to the next stage. You can always send it to a speedometer specialist for a proper fix or if your friendly with a clock repairman he could easily repair it.

Kelley

Take it apart to see. There's just a few crimps on the bezel to pry up. I fixed one where the articulated arm and the gears got out of phase.

No fix I'm aware of that will last.  I've pulled two apart that were stuck at 59,999 and one at 49,999 to sharpen the pawl that turns the gears and to clean up the gear teeth, and even swapped some parts from a donor to mine.  The most I got out of one after the 'fix' was 500 miles before it stopped again.  

They are poorly made fully mechanical odometers that just can't pull the weight of all of those barrels after the plastic teeth have worn.

Im pretty sure, i read on here a while back, about someone having the same issue...  a good whack, or a couple vibration bumps can help loosen things up and move all 5 digits over,  Its alot of effort for that old counter to move all those ticks. Sometimes it needs some assistance.

Perhaps take it apart !!! and help it roll over manually!

Im sure more experienced people will yell,  DONT HIT YOUR SPEEDO, but hey, it might work, and easier than a full tear down.

Others will chime in regarding more details IM SURE.

Goodluck

My 66 S 120+ speedo is stuck at 59999 is there any fix?  speedo portion still works but the odometer is stuck.  thanks