I recently went from 3.31 gears to 4.10 gears and was expecting to have to change my speedo gears. I checked it with my GPS and the speedometer is correct, as it was before. Is this possible with my year truck? I also expected a big change in power, but there wasn't that much, but I'd do it again. It seems to pull my camper better.

1995 F-150, 302, 4x4, auto, superchip.
P265/75R/15 tires

 

I went from 3.08 to 3.73 on my 97 4.2 5-speed. There was no doubting the change pulling out of the shop. Big difference, the truck climbed in RPM's much faster and jumped off the line. You should notice a higher RPM at highway speeds, too.

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1994 F150 XLT Supercab, 302 V8, E4OD, MSD 5200, Flowmaster 40 series, K&N FIPK

 

Sounds like you've got the vehicle speed sensor in the rear end. Cool, huh? No gears to mess with. Is your speedo/odo digital?

 

The gear change that you described (without other changes; like tires), should be very noticeable. Quickness, highway rpms, etc. Did you change them, or actually see someone do this? Sure sounds unusual!

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2000 F-150 XL,RC,LB,5.4,4R70W,3.55LS,
Class III tow/Payload #3/Convenience pkgs.,
4-wheel disc/ABS,Chestnut/Parchment 40/60,
Ford bedliner & gas/wheel/spare locks,
3" cold air box modification, Superchip,
Dynomax ultra-flow welded 3" cat-back,
3" exit Y-pipe, Hellwig rear anti-sway bar.

 

I can tell some difference but it's not dramatic. I know the guy that did the gear change and I trust him, I can hear a faint whine of the new gears in the rear. I had thought about counting the gears on the new ring gear just to be sure, but I don't remember the formula. I believe the 302 is just under-powered. The superchip helped too, but again, nothing that great.

 

Toughtruck,
Send me your email address, and I'll send you the formula for setting your speedo to make sure it is correct. I used it when I changed my tire size, and it was correct.
Rich
rdtect@snet.net