With more and more people getting junkyard Speedometers, and SHO speedos and such, I decided to do a quick little write-up on how to adjust the Odometer. This is on a SHO speedometer, the Tbird is almost identical. I got a 96 SHO speedometer with 103k miles on it and wanted to roll it back to be "correct" for my 69k mile Tbird.
First you have to remove the Needle. The back edge of a butter knife works great. Go slow and be careful not to bend the shaft.
Flip the speedo over and remove the 3 small bolts. The size is something between 4.5mm and 5mm I didn't
have the size so I used a small set of pliers. Be sure to sit the speedo on something soft so you dont break the ODO reset button.
After removing the 3 bolts you can remove the top part and unplug the small connector.
Then remove the ODO wheel housing.
On the ends of the ODO wheel the metal pin is snapped into a groove in the housing. Just pop the wheel
out of the housing. The gear on the other end will fall off so dont lose it.
At this point if your Tbird ODO works, you could remove the wheel from your tbird speedo and pop it in and put
everything back together. Or you could adjust this wheel to the reading of your choice
With the wheel out, you can use a butter knife again to pry the white plastic gear toward the end of the shaft.
Be careful of the retainers inside the white plastic gear as they will break easily. You just need to slide it maybe 1/4" away from the rollers.
Once there is a little room to slide the rollers away from each other, you can begin setting each wheel where you want it. Be careful to keep the plastic retainers all set in position with each other. Some of the rollers may not want to go back flush with each other, just wiggle it a bit and it will sync. There is a 2 sided gear between each wheel that has to mesh. If you want to you could also slide everything off the pin and re-set the wheels one at a time. Once you get it where you want it, use your fingers to slide the white gear back toward the rollers and that will lock the wheels into place. Then put it all back together the same way it came apart.
The old & the new: