The Mite
Part: 22
New Rear Axle...

Ebay Mazda RX 7 Rearend

after a long, very hot summer here in Cave Creek, Arizona, I find that the stock axles in a Sprite/Midget are good for around 100 Horsepower before they'll break. It also seems that aftermarket axles for a wire wheeled car are not readily available. I contacted Mark Williams Enterprises and they could make me a pair for $1300 bucks, and to be sure that the rear housing will handle the power I'd need a set of the double bearing rear hubs at around $400, and then I might as well get a limited slip unit for another $400. So now I'd have $2500+ invested in a rear axle for a sprite. Nope.

I searched around and found that a first genereation Mazda RX-7 rear end came with disc brakes, limited slip diff and was strong enough for 150 horsepower. I found one on ebay from these cool guys:


Old Sprite Rearend sold I had the Sprite rear end powdercoated black and assembled the whole thing with new gaskets, new pinion seal and new bearings, put the rear discs on it and offered it on ebay. Username bobnotbob if you want to see what other stuff I have for sale.
RX 7 Housing with stock brackets Here's the RX rear with the axles pulled out and the limited slip diff removed.
All the crap I have to cut off the RX7 Rear I have to cut off all these brackets and then narrow the rear end 12" to make it fit correctly
All the brackets Cut off the RX7 Axle After about 3 hours with the grinder and plasma cutter, here's the stock RX-7 brackets removed
The RX7 Rear Axle devoid of all stock bracketry The housing without all the stock brackets.
Turning the Aluminum Bearing SlugJig To narrow a rear end, I had to make jig to hold everything straight and aligned for welding. I machined a couple of aluminum blocks to slip into the bearing housings on the ends of the axles, and machined a 1.00+ inch hole in them to slide a 5 foot long piece of 1" od cold rolled steel bar through.
Aluminum Jig Slug near the bearing housing Here's the aluminum jig and the 1" bar that goes through it. with both jigs tapped into the bearing housings on the axle and the bar running through, I'll make another locating jig that goes in the area that the differential normally mounts. Then, when I cut off the ends of the axle, I can slide the bar through the 'pumpkin' jig, and then slide the bearing housings/axle ends onto the bar and weld everything up.
Stock Sprite Bearing in Mazda rearend Interestingly enough, the stock sprite bearings are the same OD as the Mazda bearings
Bearing Jigs and Bar Here's the two bearing jigs and the bar.
Cut off parts Here's the rearend with a 5.9" section cut out. I left a bit of extra material to provide some metal for precise fitment of the bearing housing/axle ends
Spinning down the endcasting bearing housing I popped the bearing housings into the lathe and spun a flat, perpendicular surface onto them so they'll line up with the axle tubes on the rearend housing
Jig on rearend This picture shows the rearend with the jig and bar through it, lining up the ends. In the area where the differential normally bolts, you can see the other jig I made to hold the locating bar in the exact position that the axles would be. The angle finder is used to correctly position the caliper brackets on the rearend.
Bad Jig, Bad At first, I tried to use C-clamps to hold the bearing jig into the end castings, but I found that the bar distorted under the clamps and did not hold the aluminum slug firmly and squarely against the bearing seat in the end casting. If I welded it like this, the whole rearend would be out of alignment.
Good Jig, Good So, I used the stock Mazda bearing retainers and some long bolts to hold the end casting square to the bar. The end castings are square to the bar, the bar is aligned inside the pumpkin housing with the other jig and the caliper brackets are correctly positioned and matched, then, a couple of tack welds 180 degrees apart
Welded rearend I checked the bar and it still rotates smoothly through the 4 holes in the 4 different jigs, indicating that nothings's warped or moved, so I took a deep breath and put down a good weld all around,
Backingplates The backing plates came mangled and I don't really need them anyway, so I cut the bent parts off and the result can be seen in the right hand side of the picture. Sanding and painting this weekend will make them look new.
Axles Here's the axles shortened 6" and resplined by Moser. Super quick turnaround and great service, if you ever have a need for shortening and resplining axles. They also redrilled the bolt pattern to match the 4 bolts-on-4" circle that the Sprite wire wheel hub has.
The Narrowed RX 7 Rear axle This is the shortened housing with axles. The axles need to be cleaned and then I have to press the new bearings onto them, and the rearend housing needs to have the leaf spring perches and the bumpstop mounts welded on, as well as the panhard bar mount. Stay tuned.....

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