Yes and no.
I would have gone with a golf cart axle in a heartbeat, but I couldn't find one for under $250 that didn't require a lot of rebuilding effort. I don't mind hard work but if I have to visit every single component of the unit and replace most of those parts, the cost savings is quickly eaten up by time and parts. I simply couldn't find one close enough to avoid shipping that was in good enough shape in my price range. Had I found one, it would have been on the kart in less than a day as I have enough big rod ends to fabricate a 4-link suspension very quickly.
I had two issues with the peerless differential. First, the ring gear and spider housing (one piece) is supported by two curved pieces of pot metal (bushings) that together form a semi-circle around the outer gear. To create a new housing for that would have been a real pain in the rear end (no pun intended) even though I figured out how to make a welded housing to accomodate the stupid round bushings using 21 separate pieces. I already have the paper templates and was going to use 13 ga steel sheet for this.
The second issue is the differential is not pinned - the spider gears "float" in the ring gear, and to pin them properly I'd have to bore a 3/8" hole in each axle shaft stub, as well as the "slip in" spider shaft that simply just lays there and is held in place by the other two spider gears on the axles. Boring into the axles in this manner was easily doable on my lathe, but crossdrilling an incredibly narrow floating spider shaft would have resulted in a a real weak part and I figured it would last exactly one romp of the throttle.
I have to rehouse the differential because the internal space of the peerless case is too close to the axles (about 1/8" - 3/16") so there is no room for flanges when I shorten the axles for an independent rear suspension. That was the original problem actually.
Combing though eBay and Craig's List I found several suitable differentials from Cub Cadet, Ariens, and other brands of smaller farm-type tractors, but all of them came with angled roller bearings and while I could use my vertical mill or the lathe to cut angled surfaces for the roller bearings to run on (these are called "cones"). It seemed like a real pain in the rear end (again, no pun intended) considering these differential assemblies were being sold without axles or axle stubs with flanges, no housing, and most of the time the sellers couldn't be bothered answering my questions regarding splines count and diameters.
I can and have cut splines on shafts before, hardened or not, but it's a lot of work, potentially without much joy in the end if I mis-index the shafts which is not that difficult to do. I just saw a lot of potential pitfalls and complexity (though, it would be fun since I enjoy using my machines) and potentially having to do it more than once to get it right.
So... I saw the Audi A4 differential for $35 plus shipping and decided with all the work that's necessary to cobble some garbage together that may break early on, this complete unit while far and beyond the concept of "overkill", comes with everything I need to make the independent rear end I wanted to make in the first place:
- A flat nose (where the torque tube originally mounted) that I can machine and weld up an adapter to hold either an electric motor or a jackshaft directly to the front of the differential housing.
- Instead of long axles I'd have to cut down and machine flanges for in order to build an independent rear suspension, this thing has the flanges already there. Because VW, Audi and Porsche are related in many ways from an engineering/design perspective, these axle flanges happen to precisely match the porsche 930 transmission, and I know I have two sets of brand new race-quality inner CV joints for it. I haven't dug them out of the attic yet but I know I have them. This alone made the differential very desirable.
- It's also very narrow. Flange to flange I'd guess it's about a foot. For a vehicle that will be 4' wide, that leaves a lot of length for half-shafts, which in turn means the angles of the CV's and/or U-joints will be reasonable and not overstressed while the suspension articulates.
- Additional "stuff". The torque tube and internal shaft came with the unit, as did the splined collar that's inside between the two. The internal shaft can be machined into a jackshaft if necessary. The mating flange of the torque tube can be easily copied to an adapter. The splined collar can be modified so it has a sprocket or pulley on it instead of a jackshaft. Or used to mate with the jackshaft. With these extra bits I have a lot of raw material to make things work in a variety of ways, and that's a good thing because sometimes the first idea doesn't work out and without extra parts of this kind I'd be back to making splined shafts and collars. Since I have the pieces, I only have to worry about half the problem in a sense.
I hope you don't mind a list, I think in lists.
But yes, a 62-lb differential assembly from a 200HP vehicle is gross overkill. But it was cheap, came with a variety of useful bits I can monkey with, and did I say it was cheap? Cheap! Even with the almost $50 it was cheap. I couldn't touch a differential of this kind locally for under $200 at any of the junkyards I visited looking for something along these lines. I originally was seeking a Toyota unit because they're much lighter, smaller, and I could take it out of the donor car with the half-shafts and CV's and cut them down and reweld them shorter to match the track of this kart. Even though welding hardened axle shafts is generally a no-no, I won't be running 100HP through them anyway so they'd survive just fine, even with my "pig welding" skills.
Anyway, that's the story about why I went with the Audi differential instead of the peerless parts. If the kart wasn't going to be 50" wide and 6' long with a wild guestimate of 800lbs dry, I would have probably pinned the peerless differential and called it a day and made a housing as I had originally planned.
The actual trigger for all this re-engineering was my dropping the slip-in spider shaft on the floor and DENTING it. A half-inch diameter, 3" long shaft falling to the floor should not DENT upon impact. And not a little ding either. It mushroomed! I cleaned it up on the lathe and intended to put a simple washer on the end to make up the minor length difference, but that just seemed cheesy.
