It doesn’t matter if you start front or back with the diffs, as they are identical. It will matter when it comes time for diff fluid though. First thing is to install the outdrives and bearings on the diff housing. There is an O Ring inside the housing, as well as a washer and drive pin.

Both front and back diffs get this treatment

Here’s what the insides look like

Next we’ll drop in the bevel gear. These slot right on the drive pins.

Its time to build the other side of the diffs. You need the drive pin, washer, o ring, ring gear, bearing and outdrive.

The O ring seats into the ring gear around the outdrive.

Here are both the front and rear ring gears ready to go.

For the diff guts, you need 4 small bevel gears, washers, and the cross pins. You also need small o rings for each pin. Caster also provides gaskets for the housing. There is a thicker cork like material, and some paper gaskets.

This is how one cross pin looks with the bevel gears and washers on it to give you an idea.

When you get both cross pins in and seated, fill the diff with fluid. The weight diff fluid you choose has a direct impact on the handling of the buggy, so check online for setups from the Pros. The book recommends 3k fluid in the front diff, 5k in the center, and 3k in the rear. I conferred with our local pro (who drove a nitro Caster for a few years) and he recommended 5k front, 7k center, and 3k rear.

Then put the two halves together, and throw some screws in…

And you’re done with all three diffs! Magic!

Something to keep in mind, and something we ran into. We initially bolted the diffs together with just one gasket, wondering why they gave us so many. Well, I tried turning either outdrive, and it felt like it was binding up internally. As it turns out, you use the paper gaskets to set the mesh of the diff gears.