The odometer crapped out on me again. I got about 5K miles on the replacement and now... plastic gears that run it can't take the wear I guess, suggestions?

There is a plastic gear in the speedometer that eventually breaks on mechanical speedometers called an odometer drive gear. This will involve removing the speedometer from the instrument cluster in the dash.

Ho, that doesn't bode well for your tank monitoring. It was a fluke, but may keep doing it, if the odometer is a mechanical meter with numbers turning from the speedometer cable by plastic gearing that wears. Watch for it to jump at the next 100 mile turn over.
I understand your reluctance to change out the fuel level sender in the tank if that is why the gauge doesn't work. It is a lot of work. But have you checked to see if it's the dash gauge or the sender unit? A couple of electrical tests could determine that. If it is the dash gauge, that is comparatively easy to replace, and you could buy a used one-they seldom go bad. Otherwise, keep tracking your miles.

Probably need to replace the dash cluster that contains the odometer mechanism. The speed, or mph is controlled by a cable from transmission to the dash cluster. The odometer or miles put on the car runs off the cable through a series of small gears behind the cluster. There maybe a broken plastic gear or something has falling off the car behind the cluster (like a screw or nut) and has caused a blockage on the small gears.

they are spring loaded and mechanical. if a spring wears out or breaks it won't work. you can replace it with another one but the actual miles won't be there or you could go with a digital set.

Mechanical odometers have been counting the miles for centuries. Although they are a dying breed, they are incredibly cool because they are so simple! A mechanical odometer is nothing more than a gear train with an incredible gear ratio.

Some odometer has a 1690:1 gear reduction! That means the input shaft of this odometer has to spin 1,690 times before the odometer will register 1 mile.

Odometers like this are being replaced by digital odometers that provide more features and cost less, but they aren't nearly as cool.

http://www.xcardiag.com/search/?q=odometer

The odometer has nylon gears. I guess your gears could have stripped out. You can find a cluster with similar miles to yours and put that in. You can try replacing the wheel but if the gears in the drive part are busted, they won't drive a new wheel. If the gears on the odometer are busted then it won't work at all.

This is tripped on by an odometer count reminding you its time for service. Technicians will reset light and it will trip once again in 5k miles

If the speedometer is working but not the odometer it's in the speedometer it's self. replacing the speedometer cluster is the easiest their available on ebay or your local salvage yard.
what happens is the trip odometer wears and sticks, theres a small motor on a circuit board with a plastic sun gear, inside the speedometer housing. it drives both the odometer and the trip odo
the teeth strip off the sun gear and odometer stops.

The gear on the end of the odometer cable probably has excessive wear which causes the odometer cable to spin. It is not completely worn out or it would not function at all; however, the fix is probably going to be the same as if it were broken; i.e., remove your present cable and replace with a new one.

Section 13-01: Instrument Cluster—Conventional 1995 Thunderbird, Cougar Workshop Manual REMOVAL AND INSTALLATION Instrument Cluster Removal and Installation

1. Disconnect battery ground cable (14301) .

1. Remove screws holding instrument panel reinforcement (017A28) .

1. Remove screws holding instrument panel lower shield (045G02) .

1. Remove fasteners holding steering wheel column as outlined in Section 11-04 . Gently lower steering column.

1. Remove fasteners holding the instrument panel finish panel (044D70) and gently pry off.
   
   
   
   

1. Remove four instrument cluster retaining screws. (Do not remove screws from the instrument cluster main lens (10887) and instrument cluster mask (10890) ).

1. Slide the instrument cluster (10849) to the right of the instrument panel opening and unhook the instrument panel harness from the back of the instrument cluster .

1. Remove the instrument cluster from the instrument panel (04320) .

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Speedometer/Odometer Federal law requires that the odometer in any replacement speedometer (17255) must register the same mileage as that registered in the removed speedometer . Since the speedometer mileage cannot be reset on this unit, affix odometer sticker to driver's door pillar and record original vehicle mileage. Removal

1. Disconnect battery ground cable (14301) .

1. Remove the instrument cluster (10849) as outlined.

1. Remove seven screws retaining the instrument cluster mask (10890) and instrument cluster main lens (10887) .

1. Remove speedometer assembly.

Installation

1. Position the speedometer assembly to the instrument cluster back plate (10848) and install.

1. Position the instrument cluster mask and instrument cluster main lens to the instrument cluster back plate and install the seven retaining screws.

1. Install the instrument cluster as outlined.

1. Connect battery ground cable and check the operation of the speedometer .

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