I have been working on getting a local guy to make the rear plates for me since I lost access to the CNC mill. Ran into some roadblocks with him being busy but I wanted to document the second stage of this build which is a stock width 8.5/8.6. Still going to be 3.73 posi with disks, 30 spline, all the good stuff from the zr2 rear minus the one bad part (being 4" wide). All this to make the wheels I wanted to fit.
Basically, Moser makes 30 spline replacement axles for GN 8.5's. 7.5 and 8.5 G body rears have the same axle bearing diameter, but you can't put 30 spline axles in a 7.5 carrier. Not sure why you would want to either but people put GN 28 spline axles in stock 26 spline 7.5's from time to time. Idea here is to re-center the stock G body 7.5 dif with 8.5/8.6 guts and use moser 30 spline axles. I started again with the 97-05 zr2 s10 8.5/8.6 but you could use a suburban, silverado or any 8.5/8.6 axle really. The advantage with the zr2 rear is the caliper parts are very similar to the 2wd stuff so a bit of mods here and there and they bolt on. If you want to keep drums a suburban/silverado center diff carrier works fine.
Axles are $260, posi is $280 from quick perf, a salvage yard 8.5 is under $150 for me, the plate was my design and free-ish. 1350 input yoke was $60, new studs were $45. Brake parts were about $75 from rock auto. The G body 7.5 rear is free. I'd say under $900 in parts. Is it a lot, yeah, but a 8.8 you are going to end up with the same amount to get axles with GM pattern and you need control arms. A 9" again is great but is in the mid $1400+ range for one with a posi and disks. You need a driveshaft either way, unless you get a nice 8.8 it's going to need rotors and pads. It's a wash cost wise but with this the geometry actually works vs 8.8 fox and you can find parts unlike 12 bolts.
Starting the build- Moser 30 spline axles right to stock 26 left
First step was to modify the 4wd zr2 caliper brackets to work on a G body axle drum brackets. I ordered new 2wd dust shields and rotors, and trimmed the shields to clear the slightly different position of the caliper. Had to make the opening wider and redrill the holes in the cast iron since I flipped the right bracket to the left and left to the right. The zr2 4wd axle points the calipers forward and 2wd points backwards. forward will hit the G body frame, backwards clears. New 2wd brackets are not available because 2nd gen F body people use 1 2wd and 1 4wd bracket for disk swaps on their rears and they are out of production. You can get lucky to find a 2wd in a yard but none of the yards around me were willing to sell just the brake parts. I did loose the e brake cable bracket doing this but need to just get a small L bracket made.
You can see the abutment bracket hits the dust shield in un trimmed config
After trimming, i aligned the park brake piston slot in the stamped hole and aligned the mounting screw to the top, used a center punch and located the new hole locations. The unintended benfit of these 4wd backing plates is that the caliper sits nearer the 11 o'clock position rather than the 10 o'clock position on the axle, which means the caliper sits higher toward the roof. This means the caliper sits in the sweet spot between the factory shock mount and the frame, a lot of 2wd blazer kits or F body rear disk swaps require a bracket to move the lower shock bolt inward. Happy accident here that solves a problem.
Old holes and my new holes
Drilled new holes in the G body axle and mounted the 4wd blazer calipers (same as 2wd), 2wd rotors, 2wd dust shields, and 4wd backing plate bracket. This is normal rear blazer disk swap stuff, just with 4wd backing plate brackets.
Stage 2- Cut the 7.5 tubes off the stock diff
I then put the tubes in my lathe and turned the OD to match the ID of the 8.5/8.6 zr2 diff. Stock zr2 tubes are like 2.75" ID and G body are 2.85" OD roughly so I just had to turn the OD of the G body tube down .1" to fit into the zr2 8.5 diff.
Half done, same thing here, I cut the 8.5 rear tube off and slipped the G body tube into the diff. Stock s10 tube on both left sides, new G on right.
I welded what was left of the stock 8.5 tube in the diff
Installed the rear into my fixture
I machined bushings to keep the axle straight for welding and a piece of 1" cold rolled rod, honestly I doubt this is needed, my fit for the tubes was a light press and they were very straight, before and after welding there was no tension on the rod.
And welded the tubes
Installed my UCA plate, cleaned axle for paint
Installed a new Yukon 30 spline carrier, all my brake parts, 1350 input yoke and sway bar from a 2dr blazer
And installed in car
