How to find gear ratio on 99 dodge ram 4X4

[DMart03]

trying to get a new rear end for my truck but i'm having some problems finding out what my rear gear ratio is. i've looked all over...cleaned up the rear pumpkin and found some serial numbers but haven't had any luck matching them to anything. in my trusty haynes manual it has a picture and shows you how to identify your axles. my axle model is 35...then right above that is reads 0639, i'm guessing this is the identification tag????? i don't have a limited slip tag. the plug reads 72-2 3723687 99201 and on top of the differential on the right side it reads GSC 5 and on the left it reads 520694319056 and the right clamp reads APO 799 S. VIN # 3B7HF12Y1XG208341

this isn't even the bad part...the rear end that i am trying to pull from another truck has less information than this...so i need some expo advice on how to tell what is what with the gear ratio. as always, i appreciate the help

 

[txbass06]

My '97 has a tag under the hood that has my gear ratio on it. There's one on the radiator core support and then one in the middle of the hood too

 

[Hotroder383]

yep, under the hood. Mine has Rear gear 3.55, wish it said 3.73 myself but I wont be picky LOL

 

[MADDOG]

My '99 had the gear ratio listed on the underhood tag as well. Mine was actually stuck to the underside of the hood.

 

[jbmobbs]

type in jbmobbs on search bar up top and i did a thread a while back on ways to find out gear ratio

 

[DMart03]

i have a aftermarket hood and and the only tag i found next to my radiator had just a bunch of numbers that looked like the matrix to me.

 

[Okiespaniel]

Some rams (like mine) have sticker in the glove box. There are normally tags on the differential cover bolts as well.

There's an easy way to do this on a non sure grip rear. With one tire off the ground and the truck secured so it doesn't roll, mark the driveshaft and the rasied tire so you can count the revolutions.
Put the tranny in neutral, grab the tire, and spin it as many times around until the driveshaft (or pinion) makes on revolution. That is your ratio.

For example, if you spin the tire 3.5 times to one rotation of the driveshaft you have a 3:55 rear.
Aprox 4 times on a 1500 is a 3:92...etc

Another way is to pull the differential cover. The ring can be marked with the ratio, or has the number of teeth of it and the pinion. Divide the pinion into the ring and the answer is your ratio.

 

[Needaram]

Mine is in the glove box as well

 

[DMart03]

got my gear ratio...now the truck i am pulling the rear end from is an automatic with the same gear ratio. can you take a rear end from an automatic and place it on a truck that is a manual????

 

[MADDOG]

Yes you can. If the swap is 1500 to 1500, no problem. Otherwise, you might see some differences in suspension mounting points.

 

[DMart03]

Yes you can. If the swap is 1500 to 1500, no problem. Otherwise, you might see some differences in suspension mounting points.

yeah it's 1500 to 1500 straight up...same year and everything, one is a automatic and my truck is a 5-speed.

Appreciate all the help fellas