Gear ratio

[Pwrcummins]

How would I figure out how to see what gears I have. I'm runnin 40s. I'm thinkin try had to be upgraded with that tire size.

 

[ghohouston]

Whats the point of a 12" lift and 40" tires? That truck cant go offroad that much, and that cant be doing anything good for fuel mileage. And there will be a tag attatched to one of your rear diff cover bolts that will say what gears you have (probably 3:73's). Now as far as if someone changed gears, im not sure

 

[oneton]

look on the door sticker.there is a axle code on it.this is not the code,but gives you a idea what it is-c9,y34,q6,etc



yours could be

31-open 3.73
c1-l/s 3.73

 

[Pwrcummins]

It's quick off the line still. At 70 mph I'm runnin under 2000 RPMs

 

[oneton]

may have 4.10's.

my truck had 4.56's and 38's would turn about 2k at 70

 

[Pwrcummins]

That would be cool

 

[SDS97_7.3]

Use the calculator at the bottom of the page http://powerstrokearmy.com/forums/calc.php

 

[oneton]

will be 32 open 4.10,c2 l/s 4.10 on sticker.

tag may still be on diff cover with info also

 

[Pwrcummins]

I know stock there 3.73. Would there be a tag if they've been upgraded?

 

[Twan]

Jake up the rear of your truck, spin the tire 1 full turn, count how many times the drive shaft turns.

 

[oneton]

I know stock there 3.73. Would there be a tag if they've been upgraded?

wont have a tag if previous owner had them changed.only way to know exactly is pull diff cover.

 

[Pwrcummins]

It says on the website that I have 2.89 gears??

 

[Twan]

It says on the website that I have 2.89 gears??

Just jack up the rear and spin the tire one full rotation and count the times the drive shaft turns.

 

[Betarocker]

If it is a LS or locker differential, lift both rear wheels of the ground and rotate either wheel one full revolution. Count the revolutions the driveshaft makes.
If the differential is an open type, only raise one wheel. Rotate two revolutions and count how many times the driveshaft spins.

An easy to way to keep track of driveshaft rotations is once you are ready to spin the wheel, tape a piece of string or twine on the underside of the driveshaft. After you spin the wheel the one or two rotations (as above), just count how many windings are on the driveshaft.