Rear Differential

[SRH916]

How can I tell what gears I have in the rear end of my truck?
Is there a casting number on it, and if so where?

[Rc 415]

If you will look on the passenger side axle tube, about 3 - 6 inches out from the center section on the front side, there will be a 3 letter/number code, hand die punched into the tube. You will need to clean it real good because they are extremely hard to find being as they are only around 1/8" tall.

[Jonboy]

As original as your truck is, I would imagine the option label might still be either in the glove box or on one of the inner front fenders. Check there, too.

[454HO]

The best way is to pop the diff cover off and count teeth on the gears. This would also allow you to visually inspect the condition of the gears and the differential, and ID if it is a posi or not. And as an added bonus, you can put in some fresh gear oil and a new gasket when you are done.

[James McClure]

I agree with 454Ho with this little addition. To save yourself the trouble of counting teeth, rotate the ring gear until you see the part number stampings, Someplace near that number you will see some numbers that look like this 15:41. 15 is the number of teeth on the pinion, 41 is the number of teeth on the ring gear. Now get a calculator and divide 41 by 15. The result is the gear ratio, in this case, 2.7333333, which is refered to as 2.73 or 273's, easy huh?

[xtreme80]

Originally Posted by James McClure

I agree with 454Ho with this little addition. To save yourself the trouble of counting teeth, rotate the ring gear until you see the part number stampings, Someplace near that number you will see some numbers that look like this 15:41. 15 is the number of teeth on the pinion, 41 is the number of teeth on the ring gear. Now get a calculator and divide 41 by 15. The result is the gear ratio, in this case, 2.7333333, which is refered to as 2.73 or 273's, easy huh?

Agreed. Even though your truck is pretty original, someone may have still changed gears in it at one point. And you can't argue with new gear oil in there

[BowTieOgre]

I have a question as long as we are on the rear diff topic. I have factory 2.56 gears and a th350 in my '80 and im thinking of going with a 700r and 3.42 gears. I think my carrier is a 2 series and the 3.42 would have a 3 series carrier...what would be involved in going up a carrier? Does the 2 series just have some spacer or something that I would have to remove?

[xtreme80]

This is what Richmond says about their upgraded gears on the Jegs website:

(Note: Will not fit 2.56 & 2.73 carrier on 80-83 Truck and Blazer.)

This leads me to believe that you would need to get a new carrier for it. I would just wait around and find someone parting a truck, and see if you can do a trade plus cash for his rear end. That's how I got my 3.73. I ended up trading my 2.73 12 bolt for a 3.73 for 30 bucks because the guy didn't care, just needed something under the truck to roll it. I got lucky and it ended up being all brand new - brakes, gears, everything.

Good deals come along, you just have to find them.