A little background to set the stage:
I bought my '85 F150 with 250,000 miles on it from of the original owner when I was 15. $700 cash. I figured it would be a good farm beater to learn on and after a few years I would get a nicer truck. Since then I have bought and subsiquenly sold or scrapped 6 other trucks. All of them either mechanically worn out or bodies rotted by the time they left... and yet I'm still stuck with my '85. The darn thing just will not quit. At this point I think I'm going to start restoring it because my wife has put her foot down and told me "no new trucks until this one dies".
In the last 13 years I have only worn out/replaced the seat, the pedal covers, the heater core, the radiator, several sets of tires, and the rear axle shafts (because apparently firewood is heavy). The original engine and transmission are still holding their own thanks to 87 oil changes and 6 gear lube changes. Hands down, this has been the most cost effective vehicle I have ever owned.
Yesterday, I wore out something else. Something I didn't think was possible to wear out before the rest of the vehicle's major systems. Just before it rolled past 512,000 miles (or rather 12,000 again, because there is no 6th digit) the speedometer/odometer died. Yep, I wore out the odometer before I wore out the rest of the truck.
I know it isn't the cable or drive gear because the speedo half of the gauge has been fritzing out since December and I think it finally took the odometer with it. Sub-zero temperatures and 30 year old nylon gear sets don't work well together. I found a replacement on eBay which has a few thousand more miles on it to correct for the winter I drove with a broken speedometer cable. I ordered it this morning and should get it by Friday.
Has anyone else ever worn out something on their car or truck that left them scratching their head?