How Do I identify gearing? 1996 1500 Magnum 4x4 V8

Hey Guys, My son lost the carrier on his rearend, and We are looking at just finding a used rearend to swap in. He has kind of been managing this on his own as I was out of town, so I am scant of details. He says there was a bolt tag on the rear diff cover but it did not identify the gearing, and he could see nothing on the door tag to indicate gearing, but I just dont know enough about Dodge pickups to know if he missed something or where to look. I see there is a 3.55 and 3.90 gear option for this year when I look on Car-part.com. I know in other trucks I have owned the two gear options would be related to manual or auto trans, but not sure if that is the case with dodge. He has an auto trans. The truck is at his house, so I am trying to get some early info before I get more involved in this. Thanks all.

You might be able to find a tag on the differential housing cover itself if it hasn't fallen off ... you can also open up the diff and the ring hear will have it stamped there too ... or the glove box, you can find a build sheet sticker ..

But these trucks almost all came with the 3.55 from factory, there were some with the 3.92s ..my pops first Magnum came with the 3.92s and it was 4x4, mostly the 2wds will come with the 3.21s for those years ...

CheechDogg.0n37s said:

You might be able to find a tag on the differential housing cover itself if it hasn't fallen off ... you can also open up the diff and the ring hear will have it stamped there too ... or the glove box, you can find a build sheet sticker ..

But these trucks almost all came with the 3.55 from factory, there were some with the 3.92s ..my pops first Magnum came with the 3.92s and it was 4x4, mostly the 2wds will come with the 3.21s for those years ...

Click to expand...

Thanks, we will check it out. He said the tag on the rear diff didnt show gear ratio but maybe he misread it..

fidelityflip said:

Thanks, we will check it out. He said the tag on the rear diff didnt show gear ratio but maybe he misread it..

Click to expand...

Yeah I would think by now it either fell off or is very hard to see ...hopefully you can see it ...

If the rear end will rotate, you can use some tape to mark your tire & the drive shaft, after raising the vehicle just off the ground

&

ratios were
3.55 or 3.73 axle ratios

GTyankee said:

If the rear end will rotate, you can use some tape to mark your tire & the drive shaft, after raising the vehicle just off the ground

How to Calculate Your Rear Gear Ratio Without Taking Anything Apart!!

How to tell what gear ratio is in your car without taking anything apart!! Calculating gear ratio on a chevy mopar ford by turning the rear wheels and counti...

www.youtube.com

&

How to Easily Find Rear End Gear Ratios

A rear gear training. 3 ways to find rear end gear ratios.

www.youtube.com

Click to expand...

Boom! that's another good way ...

So he did find a tag that says 3.5, not 3.55, just 3.5. Should we assume it is infact representing a 3.55? We cannot spin the rear as it is jammed up. I dont think he could see a ration on the ring gear.

Yes, that would be the 3.55. If everything is original you can also look on the sticker under the hood. Right by the latch there is a basic options list that will show the factory equipped differentials.

If it is all apart, count the teeth on the pinion gear and ring gear. Divide the ring gear # by pinion # and that will give you the ratio.
For Example:
42 (ring gear) ÷ 12 (pinion)= 3.50 ratio

If it's 4WD wouldn't the front diff have to be the same ratio?
May be a tag on that.
Some models had a paper wraparound on the right rear axle tube just behind the backing plate, could look there too.