Hey Guys,
I just ordered some stuff to prototype a ball diff. I've got two V8 pushrods coming, one 5/16" and one 3/8" O.D., from Ebay. They both have 0.080" walls, which should be strong enough, but the wall thickness only permits a 6-32 threaded rod (for adjusting the diff) to pass through the 5/16" size, which is a bit of a concern.
The 5/16" pushrod was $5, and the 3/8" pushrod was $7. Both are new. In quantities of 10, the cost drops by about half. That's thrifty, even for a tightwad like me!
I've used pushrods as axles before, and if I recall correctly, the O.D. is pretty accurate. But we'll see if that's true in this case.
I also ordered some 8x12mm and 3/8x5/8" bearings from TQ. As aarcobra mentioned, they are darn cheap! The 8x12mm should fit nicely inside the rear wheels to permit the right side to rotate freely on the 5/16" axle. I'll also use them for spacers on the left side wheel, even though that doesn't need bearings to the axle, because they are so cheap!
Next up is to get some clamping collars on order to support the inside diff ring.