So the 2000 Miata 3rd member triggered a giant domino-effect clusterf--k. I am just now seeing the light at the end of that tunnel. Unbeknownst to me, I have a 1983 RX-7 rear-end housing, not the 84-85 I wanted. Thanks, junkyard! Two differences: -bigger bearings -26 splines from 24
I learned this when my axle shafts clunked around inside the newly-installed Miata 3rd (26 spline). OK, I thought, I will get custom axle shafts with small bearing size/26 spline. Moser Axle says "can't do it", after a month of miscommunication. My next idea was to get 84 housing ends, machine/weld some adapter parts and weld into the ends of the 83 housing. This will increase track 5", not a big deal as I was using big wheel spacers to use FWD wheels.
I got 84 ends from an RX-7 guy in Tennessee, and ordered 2.5" longer 84 rx7 axle shafts, 4x100 pattern, from Moser. I made little adapter pieces from 1/2" wall DOM, pressed them into the housing ends, had a buddy TIG them, then machined some more.
I got the shafts from Moser. Two problems: -No 4x100 pattern, just a weird 4x127. -There was only about 1/2" of spline interface into differential. This is probably not be a problem with the Moser axles, and may be the case anytime a Miata 3rd is used in an RX7 housing.
I decided getting another set from Moser would take too long, so I machined these to work. I made a drill guide on the mill, and modified my drill press to accept axle shafts (big hole in the table).
I machined 7mm off the bearing stop to get 7mm more spline interface, and will use 7mm spacers between the axle flange and the brake rotor to compensate.
I then hammered the adapter pieces into the 83 bearing races. I machined an aluminum puck to press on an axle shaft so I could use it as an alignment fixture while welding. I also used bolts thru both brake tabs. I then welded away, stitching to avoid heat/warpage.
Now I just have to finish my brake brackets, a little paint, and I may be on the road again.
PS1: Yes, I probably should have just given up and went back to the 3.90 3rd, but the 83 axles would have been a weak point with the new motor. PS2: Yes, I probably should have just started over with a fresh 84 housing, but there is a LOT of custom bracketry on there...
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Last edited by squarefour on November 20, 2019, 4:35 pm, edited 2 times in total.
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