What gear ratio do I have?

[Libertad]

Can anyone tell me what gears I am running if I have:

Casting #s

Rear Axle:
GM14 (full floating)
CFD
345
3977323




Front Axle:
Dana 44-8F
620121R




Transfer Case:
NP203
ratio 201
serial 5 20 76
assem no 336990


Running 15/39.5-16.5LT Super Swampers





Thanks in advance for any info.

[Stocker]

Other than pulling the diff cover, counting the teeth and dividing the number on the ring gear by the number on the pinion...

Chock the front tires, jack up the rear end and use jackstands, leave it out of gear and parking brake off.

Assuming a pegleg, rotate a rear tire exactly one rotation and count the number of revolutions of the driveshaft. If it's a posi rear, I *think* you double the number (of driveshaft rotations).... or maybe divide by two, I don't recall. Someone will step in and say for sure!

[Blazer1970]

If you can get the BOM off the front axle the OEM ratio can be determined from that. It is stamped on the axle tube facing forward just right of the pumpkin.

[raycow]

Originally Posted by Stocker

Assuming a pegleg, rotate a rear tire exactly one rotation and count the number of revolutions of the driveshaft. If it's a posi rear, I *think* you double the number (of driveshaft rotations).... or maybe divide by two, I don't recall. Someone will step in and say for sure!

Almost, but not quite. If it's an open rear, jack one wheel off the ground and turn it exactly TWO revolutions. The other wheel must remain on the ground or otherwise be prevented from turning. Your axle ratio is the same as the number of driveshaft revolutions.

If the wheel is difficult or impossible to turn, you probably have posi. In that case, jack both wheels off the ground and turn either wheel ONE revolution. The other wheel will turn with it. Your axle ratio is once again the same as the number of driveshaft revolutions.

Ray

[powerdriver 1958]

The most common gear for a square (from what I have seen) 3/4 4X4 is 4:11,Did you put the super swampers on it or buy it that way?

Best way to know for sure is a tooth count.

[Libertad]

Originally Posted by powerdriver 1958

The most common gear for a square (from what I have seen) 3/4 4X4 is 4:11,Did you put the super swampers on it or buy it that way?

Best way to know for sure is a tooth count.

Thanks for the responses! I will try your technique RayCow.

Powerdriver, I got the truck with the super swampers on it. She also came with 3 38" Ground Hawg tires that I would like to put on if I could trade these 4 super swampers for 1 more ground hawg..