Axles. Ugh. My original plan was to press out the Miata hubs and press in mk2 VW guys. The VW hub OD is the same as the Miata, and the axial lengths are within 3mm. Also, perhaps, I'd get lucky and find something that'd match up with the funky Passat 6x114mm bolt pattern. With the a control arm tacked together and the motor mounts in, I started measuring up for axles. The Passat axle outputs from the Passat transmission are shifted towards the driver's side. I thought the motor was pretty centered in the chassis, but the driver's side axle needs to be about 2" shorter than the passenger.
So, what do we know:
- VW hub presses into Miata knuckle. I got my hands on a VW axle for test fitting - no way that is going to work.
- Passat axle bolt pattern is strange 6x114.
- 94 Miata has a flanged axle that does not match the Passat bolt pattern. I believe it's 4x110.
- This is the same transmission as a Boxster, right?
The last statement - not 100% true. From my research, the Boxster uses a "108mm" Porsche CV, but this refers to the CV OD, not the bolt pattern. Bolt pattern is really 6x94mm. I started going down the rabbit hole of: How do I make use of the custom VW/Porsche axle shafts, Porsche 930 CVs, and somehow mate that to the Miata upright. A week or two later, still no solid plan despite hours of internet wrangling.
Here's what I think i want to do. Adapt the 6x114mm Passat pattern to 4x110 Miata. Laying this out in CAD shows that there really isn't enough ?room for bolt heads on the Passat side of the adapter, and there's only about .180" clearance on the backside of the Passat CV flange, so bolting in the adapter from the inboard side of the CV flange isn't an option. I can weld and redrill 2 of the holes in the Passat flange to match the Miata. A stock '94 Miata axle looks like it'll work perfectly on the passenger side. I just need something that's 2" shorter on the driver side. I really should measure the flange to flange width of the Passat and my Miata diff.
Anyways, here's where this GRM braintrust showed it's value. While researching cutting CV splines, I stumbled on this thread:
https://grassrootsmotorsports.com/forum/grm/cv-axle-splines/62851/page1/Which brought me to this goldmine:
http://interparts.com/index.htmUsing their catalog, I found the interchangeability of the Miata outer CV
Attachment:
miata cv.jpg
I knew about the outer 26 tooth spline, but not the inner 22 tooth. Fortunately, they have an application list for CV axles with the spline count. Unfortunately, they don't list a Miata axle. Luckily, I happen to have a couple around the shop with the wrong inner CV for me. A couple minutes later, I've harvested an axle shaft.
Attachment:
IMG_20180107_172907135.jpg
OK, so I'm now looking for a Mazda family, 22 spline at both end, axle shaft that's somewhere around 17" long. Well, what do you know:
Attachment:
axle shaft.jpg
MX3, Protege, Sephia as listed ought to do the trick. These also have the same outer CV as the Miata.
The final plan for the driver's side axle (final until I get all the pieces and figure out it doesn't work):
- Devise some sort of VW to Miata adapter
- Pass'r side: stock '94 Miata axle
- Driver side: Short Protege axle with outer CV, swap the inner CV for a flanged Miata unit.
That's where I am. I think I have a plan. It seems solid enough. I'll order up an axle this week and see if it does the trick. I have a few hair brained ideas for backup plans - but I'm trying to avoid welding axles as much as possible.