Help Identifying rear end

[Green72GMC]

I was wondering what gears I have in the rear end. I scraped off the greased on dirt and found these numbers on the right side of the truck facing the cab if you are facing the tailgate:
3896839
Then under it, it had an N.

I doubt it is the original rear end that came with the truck.

[Hutch]

Green72GMC
Identifying rear ends can be a challenge:
There were a lot of different ones used on these trucks.
A lot depends on the series 1/2 ton 3/4 ton or standard trans or automatic.
Here is a link that will give you an idea of what to look for:
American Classic Vin Decoder
This is for 72 Chevrolet trucks but the number that you need will be stamped on the axle tube and will have three letters as a prefix then some numbers.
I beleive that this number is on the passenger side axle tube faceing the cab.
You may be able to identify the housing through the numbers but the inside gears could have been swapped on a previous rebuild.

You might also check GMC Pauls web site at:
GMC Pauls Vin Decoder

Paul has a lot more detail on the GMC line than others, it seems that the Vin numbers decode differently than ones for the Chevys.

You can always take the cover off and count the teeth and do a little division to find out what your gear ratio is or post a pic to see if someone recognizes it.
Try to supply as much information as you can with the pic and maybe even a pic of the Glove Box data sheet.


Have Fun

[Longhorn Man]

I always say it is a good idea to dump the oil out of the rear and count the teeth.
1. You'll KNOW the gearing...it may have been chainged since the truck was built.
2. You'll KNOW the oil is fresh, and not some 20+ year old crap.
3. You'll KNOW if there is any metal shaveings in the oil instead of waiting for the gears to break in 1/2

But that's just my thinking.
And yes, even as cheap as I am...I have always dumped the oil out of every rear wheel drive diff that I have owned right before putting it on the road.