Differential gearing identification?

[adrenalnjunky]

Moved this to stock, since it fits that category best IMO-HJ

Does anyone know how to tell what gearing is in a stock front differential? Is there any indication on it at all?

The reason is that I have a front diff on it's way to me from an ebay seller. The diff came out of a 98 model that had a fire in the interior so the truck was totalled, and the glovebox RPO code list was destroyed in the fire. The truck was stripped of all driveline and then the shell discarded. That way I have no VIN # to go by either.

If the Diff has 3.73's I'm going to swap the rear gears on my truck, and swap that diff into my truck, but if it's a 3.42, I'm going to have it built up with 4.10's first, and then let it sit around while I save back up to have the rear end done.

I am only paying $60 for the front diff, including shipping costs, so it's not that big a deal if I end up doing nothing with it at all.

[AZS10Crew]

There's some way to count the teeth or something like that, but I can't remember what that was. Are there maube casting numbers or something like that?

[adrenalnjunky]

I'm waiting for UPS to drop it off next week. I'll get a better look at it all then.

The big problem with the front Diff housing is that there is no access cover that I am aware if, it is a 2 piece design and has to be completely disassembled to get to the ring and pinion.

Large image

made the large image a link , the file size was acceptable, but the format was pretty big-HJ

[Dragonmaster]

hook the pinion up to something that you can set the rpms on and then count how many thimes the outer shaft rotates in 5 minutes, then do the same for your existing one. If it spins more times, higher gear ratio, less times lower gear ratio. the only way of knowing for sure is to dissassemble it if you don't have the vin# or rpo code. Chances are thought that it is most likely a 3.42 if it was not custom ordered and it is a 4x4 non-z

[HenryJ]

Soes anyone know how to tell what gearing is in a stock front differential? Is there any indication on it at all?

There is a way.
It is easier for an axle that is mounted in the vehicle , but you should be able to determine the ratio with a little help from a friend.

Make a mark on the pinion yoke (where the driveshaft would attach) and a refrence point on the case. Now both axles must be engaged (4x4 locked in) for a front differential, then rotate both axles at the same speed and timing one revolution, while counting the number of times the pinion rotates. You must keep both axles turning at the same speed so thast the spidergears do not allow for an incorrect measurement. If it wasn't for that, or if you had a locker or posi you could just turn one axle and the other would rotate with it.
It is easy on a vehicle, you can just roll the vehicle in a straight line ,one revolution, while counting the number of rotations the driveshaft makes.

It should not be too hard to tell what ratio you have. If the pinion rotates just under three and a half times to one rotation of the axle,you have 3.42. If it rotates almost three and three quarters you have 3.73.