7.5, 8.8, & making it all work
 

So I have seen a lot of info on 7.5's, 8.8's, and axles all in various threads and build logs but I wanted to try to ask some questions in a different wording to try to consolidate a lot of it in into one thread.

-For the 7.5 & 8.8's:

How difficult is re-fab on the rear sub-frame to get either to fit?

Are there any axles that will work out of the box with either on a miata without needing to be machined, broached, or otherwise modified? (not limited to miata hubs)

-if not, what available options are out there currently?
-what sort of modifications are needed to make it work?

-what hubs/etc work best with various options here?


Lastly, what sort of price ranges do all these axle/diff options tend to fall into?

I know that's a lot of questions that depend on a lot of different variables, but any input, advice, and tips would be greatly appreciated.

Not directly able to answer your question, but offering an option: rather than trying to reinvent the wheel, I bought Martin's complete 7.5 rear set up with axles and mounts for around $1200.

Say what? If you consolidate it all into one thread it robs the hours of research and pondering it takes to work through these questions and takes all the challenge out of it. I say NEVER for this is what separates the men from the boys, the wheat from the chaff, the guys who build cars rather than just go order a new Mustang!

OK I have not had any coffee yet today...

OK had coffee now so I'll play nice :D This is a great post and I was just razzing you above in fun... ;)

The kits are not difficult and only require a couple of welds. You can pull the rear cradle and take it to any welding shop and have it done for a few bucks. Most independent auto repair shops or even a decent exhaust shop should be able to do it as well.

If you mean to build your own that completely depends on your level of skill in fabrication. When I started my build I would never have attempted to build the mount myself but now that I have the experience of the build and welding there is no question I would fab it myself.

No there is not. At least not that I have ever seen. I think it's safe to say after 20+ years of conversions if there was some one would have found it by now and it would be very big news!

When I went down this road I looked under every rock too and found there is 3 off the shelf options for both mounts and axles. Martin (Monster Miata), Flyin Miata (V8 Roadsters) and Boss Frog. Monster offers kits for the 7.5 and 8.7 Fords. Flyin Miata offers kits for the Cadillac diff and Ford 8.8 and I think a couple of axle options. Boss has a couple of axle options for different power levels and uses the Ford 8.8. All 3 do the mounts very differently with advantages and disadvantages to all.

Beyond off the shelf there are plenty of cars that have been built with Factory Five or FFR Cobra axles but in my investigation that is neither cheaper or easier so I did not spend much time looking at them. There are also plenty of fine builds that are DIY done like the road kill guys did or done by a local drive shaft shop with the chops to make axles with a Miata hub on one end and T bird on the other.

Best is a big mine field with dozens variations on how to get it done and even more variables on your car, goals, skill level, budget etc. I'm not sure anyone can really say what would work best for your situation but I can tell you why I did what I did if that helps.

In the end I went with Martins set up for 3 reasons. 1, he has 20+ years of conversion experience and I knew his stuff will never leave me on the side of the road, 2 it was the lowest priced option, 3 I had just come off a summer of blowing up 3 rear ends in my donor Camaro and was not about to cut corners by trying to make my own.

Now that being said if I was to do it again I would have done it very differently and this may be the most value any of us can bring to the discussion. At the time I thought building a mount was beyond me but I was very wrong and I wrote quite a book on my blog about that. Doing one now I would not use any of the off the shelf diff mounts because IMO they all are lousy designs and grossly over priced. Mike Moningers excellent design is by far the most intelligent design I have ever seen in a diff mount and what I will use on the next build. MiataV8 Conversion: Rear subframe .

For axles if I was doing it again I'd probably follow in Mikes foot steps too like V8 droptop is and convert to 5 bolt lugs. But for staying with the 4x100 you can't beat Martins axles especially if he would sell just the axles and hubs without the boots.

True that on the variables and I hope what I said helps!

update:

after doing some more digging, I think Martin's kit, or at the least parts from it makes the most sense. Now I just have to find the time to call him! haha