94 f150 2wd 300 auto. Just swapped in a 3.73 form a 3.08. I'm guessing I need to recalibrate the speedo. Any idea on the number I need to use? I can find charts on tire sizes but not gears. The tires are 225/70/15. Thanks.

 

No need to recalibrate for a gear swap, only for the tires. This is because the tone ring bolted to the carrier is what is used to generate the vss signal (instead of the old setups that used the trans output shaft). So the only correction needed is for tire size when going from axle rpm to vehicle speed.

 

If the speed sensor is on the top of the rear end you shouldn't need to change anything. I went from 3.08 to 4.10 and speedo stayed correct. Mine was a 95 so maybe that's the difference. You would have to change the setting if you went to different tire size though. Thought I had read something at the time that said it would only allow you to change it like 8 times or so.

 

It is 3 times for a 1992 and 6 times for the 1993 and newer OBS trucks.
But there are ways around this also.

 

Thanks guys. Guess that's why I could not find a chart for gear swaps. It makes sense now that I have thought about it. Took me a minute to understand how it could not effect it.