I'm selling my 12v and I'm trying to find out what gear ratio is in the rear. It's a Dana 80, 3.5 axle ratio according to the sticker under the hood. But one of my buddies swears it's a 3.73 or 4.10 due to the speedo/tach. It's about 2100 rpm's at 70mph. Tires are 265/75/16's.

 

At 70MPH my RPM is at 2400.I have 4:10 gears.

 

I believe this to be the case-Automatics have 3:55's & manuals had 4:10's! The only way this may be different, if a former owner changed the gears or the factory changed the truck specs in mid production. Ether way, you can jack the wheels off the ground, put the truck in neutral, put a mark on the driveshaft & a tire. Spin the tire 1 time around and count how many times the driveshaft spins. 3-1/2 times is 3:55 gears, 4 times is 4:10 gears!

 

Does your truck have an auto or a manual?

If it is a manual, you probably have 3.54s. That sounds about right.

A manual with 4.10s will turn... HIGH RPMs at 70MPH.

 

It's a manual..thanks for the tips. I might try the jackstand idea to just narrow it down.

 

Those RPMs are right for 3.55s. You can get either gear ratios with any of the transmissions, not quite as rigid as with options as they are now.

 

with ur tires and a nv4500

3.54's
71 @ 2000rpm

4.10's
61 @ 2000rpm

So it sounds like u have 3.5's

 

Have you looked for the tag attached to the diff cover? It will have the ratio on it.

 

If you can't find the ratio on the diff tag, call the dealer with your vin number. From that they can pull the build sheet on the computer and you can get ANY information you want. It will have all the details.