Ford 7.5" Diff Swap Thoughts...
 

Alright so I'm considering doing a ford 7.5" differential swap this summer. I'm still looking into this and reading up on them, but it's looking more and more like the answer as far as the rear diff goes. Fact is the entire rear end back there is just not built to take the power. Be it the stock ring and pinion, or a torsen, or the axles. They're all weak points and will break under hard launches. If I could find a forged R&P and get some custom axles made, and a RX7 LSD too, it would probably be fine. But even that would be expensive and high strung.


It's a commons swap to do a Ford 7.5" swap on a V8 conversion. Panache has been using this setup for years and they sell a kit that's V8 swap specific. Several V8 guys are putting down big power number numbers using a 7.5" diff and Panache axles w/ re-broached hubs and report great results. Granted some are using the 8.8" ford diff for added strength, but the consensus I'm gathering from the V8 conversions forum at m.net is "only the most extreme V8 drag car would really benefit from the 8.8, the 7.5 is stout."

That said, the Ford 7.5 is looking awfully appealing right now. I can get the actual differential for cheap at a local u-pull-it yard. I could probably build everything to hold the differential as well. But I could not broach the factory hubs, nor could I do the axles the right way. So I would at minimum, but buying axles and hubs from Panache.

Little info for those wondering "why?". The ford 7.5" is proven to be tough in V8 applications. And a badass R&P is like 350ish NEW and I can pick whatever ratio I want as there are several available. But I probably wouldn't as the car I'd get the 7.5" from has 3.27's from the factory. Perfect. Limited slips are available and several older vehicles had a ford clutch type LSD from the factory that will swap into the 7.5" much like the RX7 lsd swap. Also, if the ford unit were to break, replacing it is CHEAP. I could literally go to the local yards and find 20 of them at any given time. They're plentiful and in low demand. So it would be nothing to keep a spare around. They're like 50 bucks I think. In time I can probably find a LSD at the local yard too. I've seen them more than once.

And for those still wondering "why?", I'm going to build a motor this summer and turn up the boost. I want to get to at least 350whp and it be somewhat reliable. Right I'm around 250whp or better and the power is nice, but I hate not being able to beat on it. Sucks being afraid to grab a gear. I know the transmission will have to be addressed as well though. That's another thread…

I emailed Panache earlier today to a price for just axles and hubs and a price for the entire kit. So we'll see what they say.

your expecting to break axles?

Yeah, I drag race the car. I'd like to be able to put a set of slicks on it and beat on it and not worry about breaking an axle. People that drag these cars w/ slicks have broken axles.

didn't know

I've been thinking about this, but the price of axles makes me run!

Yeah, I can imagine they aren't cheap. I could try to make my own, but I dunno. I could probably do it, but they wouldn't be perfectly balanced or heat treated. And if I add up all the time I'd have in making them, it probably wouldn't be worth it if they're available.

I emailed him but so far, no reply. I talked to a guy with martin's kit and he said he's terrible with email and that I'll probably have to call him. So if I get no reply by the end of the day, I'll call them.

Pat, any thoughts given to the TII rear end? MiataRoadster has hubs that let you run stock TII axles, and it will bolt up to the stock wing mounts which makes mounting in general a lot easier.

Not really. Not too familiar with that actually. The ford part was appealing because it's cheap, easy to find, ring and pinion, LSD's, etc are cheap. I have seen those hubs you speak of and they're like 400 bucks! Dunno what a TII swap would cost when it's done, but if it's close to the cost of the ford, I'll take the ford. Have you got a balllpark price for a TII swap? Curious.

So; does anyone know the price? I'm also curious.

IIRC, those hubs from miataroadster are 400 bucks alone. I would imagine a TII rear end w/ axles is probably 400 also. That's too close to the cost of a ford 7.5" to catch my attention. The guy I emailed never got back to me. I'll have to call him whenver I don't have 11th billion things to do during day.

I figure the RX-7 TII diff should be relatively easy to find locally. Plus, shipping diffs gets very expensive in my case.

Mustang inner CV's + Miata outers + machined tube + rosette welds = DIY axles with no broaching. I can't believe that you are even sweating this issue. What do they want, $1K for a set of axles? You can have it done locally for $250 max if you pay for machining and quality welding. You can get the mustang axles with the 7.5, you have yours. Done deal.

I've considered this for a Lexus 4.0 swap on my other 99.

Believe me, I've considered that method. It's doable. I just figured it wasn't the "right" way to do it. But if it was welded well it would probably be fine for my 4 cylinder.

I wish there was an easy Ford swap, I would have got it in stead of another Torsen, now I'm in to $1300 in Torsens....so far.

Coming from the mustang world, I'd do the 8.8., since you are talking drag aracing and slicks. I may cost you a little more, but at 350hp you should have to worry about it anymore

Two concerns-

1) with Steins method, cost goes down, but how strong are the miata outer CV's? I've heard of people breaking axles with slicks. If it did it this way, the stock miata outer CV's would be the new weak link.

2) My research from all the V8 guys is that a 7.5" is strong enough and they don't break. I can buy 8.8 stuff locally for the same price as the 7.5. But I would imagine the physical outer dimensions of the 8.8 are larger, which means more work to fit it and ultimately less room for exhaust. I'd rather have the 8.8, but if it's not needed, I don't want to overdo it for nothing.

did we ever get prices on these parts?

that is your first post?:bang:

"we"?

Seriously?

GTFO.

wow you guys are nice

i just started doing research and am gathering a complete total cost before i dive into the project

thanks for the help???