speedometer calibration

[Shotgun]

I have a '76 TA that I changed the 100mph speedometer for a 160mph from a '70 model. It reads 11 mph higher at 60 mph, according to GPS. It is the Super T10 4 speed, and original 3.23 rear gear. Would anyone know what the original drive/driven gear would be? Color/tooth count? I am hoping to keep it simple, and just replace the driven gear. Anybody done this? Thanks

[81Blackbird]

Just cut out the speedometer and replace it with a GPS and call it done. )

[Shotgun]

Always the wise guy. Now, go back to work.......

[b_hill_86]

Here is some info that may help you

https://www.tciauto.com/speedometer-gear-calculator

You can also pick up a set of the driven gears pretty inexpensive on eBay. https://www.ebay.com/itm/GM-SUPER-T10-MUNCIE-18-19-20-21-22-TEETH-SPEEDOMETER-GEAR-SET-W-BULLET-/154781813798?mkcid=16&mkevt=1&_trksid=p2349624.m46890.l6249&mkrid=711-127632-2357-0

That set is lacking the smallest, a purple 17 tooth but you wouldn’t need that likely. You need one with more teeth to slow your Speedo down.

Question though, did your original speedo read correctly? I could be wrong but I thought the speedo themselves are geared different internally which wouldn’t require any external changes (drive/driven gears) if you swap them. Like I said, I could be wrong though.