If you've been following along, the donor axle rods were '85-'88 Fiero passenger side axles from a manual transmission car. The reason Fiero automatic transmission axle rods can't be used is because they're only 23.8 mm in diameter; too small to be re-splined for the 27 mm major diameter of the Cobalt tripot spider.
The machine shop cut one donor axle rod to 425 mm long, and the other to 485 mm. Then he loaded them separately into a special dividing head jig on his lathe. The dividing head holds the axle stationary in the lathe while one spline is being cut, then allows the axle to be rotated in any number of steps to cut whatever number of splines are needed for 360 degrees around. Here's a photo that shows how the jig holds the axle while the mill in the background cuts one tooth:
And here's a view from the other end of the lathe showing how the lathe just holds the axle while the milling head does it's job.
The machine shop owner said that the Fiero axles were made of high quality, very hard steel. His carbide cutter had to be run three times through each spline to remove enough material, and he needed two bits per axle since the material would dull the cutting edge. Here's a close up of the cutter bit in action:
I figured I'd walk out with two axles in my hand that day but Murphy's Law reared it's ugly head on the second axle. Before loading it into the lathe, he gave it a quick whirl on a roller jig to test the straightness of the axle rod. My second one was slightly bent and of course would wobble like a Weeble in the lathe making it impossible to cut the splines at precise depths. That's when I found out passenger-side Fiero axles had become rarer than chicken lips.
Plan B was to go back to the junk yard and find any axle that was large enough in diameter and long enough to be cut down and re-splined at both ends. The most promising axle was the passenger side one from a '96 to '07 Dodge Caravan, Grand Caravan, & Plymouth Voyager. It measured 26.8 mm in diameter and was plenty long.
Even better, (and much to my surprise) when I removed the CV and tripot joints from the Caravan axle rod, it had 32 splines at both ends just like the Fiero axle rod. Even the snap ring groove was in the right place and was the right size.
That meant I could cut the axle rod to length and have new splines machined onto only one end as I did with the Fiero axle. Here's what the 25 splines on 27mm looked like on the cut down axle rod. Ready for the Cobalt tripot joint spider assemblies:
Here are all the pieces, less the tripot joint cups:
I greased up the innards of the CV joints and slipped them onto one end of each axle rod until audible clicks were heard signalling the snap rings had seated into the grooves:
Then I slid the boot into place and used some special clamps to retain them:
Next came building up the tripot end of the axles. The boot goes on first, then the inner snap ring, then the spider assembly:
And finally the outer snap ring goes on. Here's what both axles looked like ready for the tripot joint cups.
Normally the cups would be installed onto the axles next, but I had installed the bare cups onto the car earlier:
This allowed me to install the axles dry, and watch the tripot bearings as I cycled the suspension through its full range of motion. I checked to make sure the rollers remained within the allowable travel limits inside the tripot cups. Here's the RH tripot at full jounce:
Once both axle assemblies were tested, I greased up the tripot joints and clamped the boots in place. Here's a photo of the passenger-side tripot joint seated in the jackshaft:
And here's a photo of the driver's side axle and suspension at ride height:
With the cradle back out of the car, and the axle prettied up, here's a final look at the complete rear suspension:
This pretty much ends this section on the rear end. There are still lots of other rear chassis systems to address such as fuel, cooling, and exhaust to name a few. I'll cover them along with all the front chassis systems in a separate section specifically for chassis systems. Next up though, is the redesign of the front end. See you over there.