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I kind of like mine it bolts right in.
LOL understatement of the year so far. We all kind of like it too. That is radddddddd.

Is there a wait list and expected cost range for this beauty or are you just building yourself a fleet of bulletproof mk2's?
 

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Discussion Starter #22
It's a IRS Ford 8.8. I built 5 of the front bracket so yes the plan is make 4 more. I have 3 of the stock front crossmembers to use as cores now so I can rotate them out pretty quickly when ready. It's a pretty simple mod, but it needs to be jigged correctly What's holding me up right now the arms. Having a hard time finding a local machine shop that will even give me the time of day. In the end pretty much all the parts are readily available off cars they make now. What you end up with is much stronger drivelines, multiple sway bar options, cheap brakes, many sizes of brakes, and most are much cheaper than the Mk2 equivalent.
Arms, so you are trying to build a kit with new arms to get I assume built in adjustable camber correction, a new hub with stronger stubs and better brake options? If you are going to open up sales of that diff mount setup, I think many could get by with just that and the swaybar. If one has already done the camber mod and has rust free arms (and maybe JK rear brakes), all such a person would need is custom CVs to mate that to the stock hubs and they'd be good to go. There are certainly more then a few out there sitting in the power range Ryan is where they are breaking 7.5 diffs and axles but not stubs.
 

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The stubs are tough - they are actually slightly larger than the pinion splines on the 7.5" diffs, so it would take plenty of power and some kind of mechanical locker or a welded diff/spool to get that much torque output on one wheel. Plus STICKY tires.
 

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Arms, so you are trying to build a kit with new arms to get I assume built in adjustable camber correction, a new hub with stronger stubs and better brake options? If you are going to open up sales of that diff mount setup, I think many could get by with just that and the swaybar. If one has already done the camber mod and has rust free arms (and maybe JK rear brakes), all such a person would need is custom CVs to mate that to the stock hubs and they'd be good to go. There are certainly more then a few out there sitting in the power range Ryan is where they are breaking 7.5 diffs and axles but not stubs.
Plan right now is to modify the stock arms by lobbing the end off to keep the cost down. Even doing that it's still quite expensive. I don't think honestly anyone is going to be that interested in the rear arm option since I'm basing it around 5 lugs. Yes the two upgrades are mutually exclusive. I think its a neccesity since the weakest link in the car will be the stubs and I'll be royally screwed if I break one of the MS123 ones.

Cost wise the rear 8.8 conversion is pretty comparable in price to all the other ones out there I've found. A lot depends on how fancy you want it. Do you want powder coating, camber eccentrics, a DIY option. etc. Right now its too early to promise much since it has to work first...
 

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Discussion Starter #26
5 bolt, if its 114.3x5, would appeal to many I think. Though less so then in the old days when there was barely any off the shelf wheels available. But a modded arm solution has less appeal to many. It would be awesome to have an aftermarket bolt in arm solution for sure as rust is a problem here for us too.

I'm just going to go mk3 irs as others have done, but the l really should pick up an is300 irs and adapt that instead for the good of the community. It should work just as well if not better (almost certain its lighter), but I already have all the mk3 stuff so cost and risk wise it makes little sense for me. Though there are better aftermarket parts options and supply for those cars, hmmmm.
 

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Rule of thumb, aluminum is 1/3 as stiff as steel. Not sure about its workhardening properties in comparison but they should be similar, 1/3 as good.
 

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View attachment 8121 View attachment 8123 View attachment 8125 View attachment 8127 View attachment 8129

So as you can see, these diffs use axles almost exactly the same dims and size as ours. That's sort of a Minus really since our half shafts are a weak point, but we do have solutions for that and its kind of appealing that our half shafts could pretty much have the holes drilled up one size and it looks like they'd bolt to this diff. Yeah I know you'd still need to get custom axles made since this 8inch diff is notably wider, but still kinda neat. Anyways, I think the diff is in the same boat as the IRS. The mounting points are off by 10cms, which would put the bolt holes right on the ends of the aluminum. This one piece aluminum case\wing ear mount arrangement looks hella strong, but it does complicate swaps. Technically you could cut the mount and tig weld in an extension on each end though. And the sleave inside those diff bushings on just the diff are exactly the same size in both diameter and length for our studs. Thats a mk2 stud slipped in in the pic! Also a mk2 axel for comparison on that one photo. As for mounting at the front, get this, these diffs get all their strength from the back mounts, the just bolt to the front half of the subframe with a little ear tab and 2 bolt holes and an isolator bushing. That long piece at the very front of the diff appears to just be a resonance NVH thing, no holes on it, the 2 bolts further up are the mounting point. If one were to mod one of these diffs to fit, in theory you could get away with just hacking off the cradle from our subframe, then welding on a simple little ear like the Mazda suspension subframe.

Anyways, its just an idea so I thought I'd share some info. I think there are probably better options out there for ease of swapping and availability, but it was pretty cool to see how Mazda was doing things back in the 80s too. Although this is from the end of the 80s when Toyota already had a double wishbone IRS out for several years, seeing all the extra tech put into a trailing arm setup was still kind of neat.
That rear camber by the hub is well smart. Like that idea and never thought about that as an option before. Might have to copy that!
As for the 8" diff upgrade, that's probably worth looking into a lot more. Bet finding a subframe in decent condition won't be easy though. Offset hole subframe bushes are easy enough, but body clearance would be the killer as you said.
Keep playing with this though, as even if it's just the rear wishbones - i really like the camber adjustment possibilities
 

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Discussion Starter #31
Yeah there's that too, another incentive to just go is300. I was going to reinforce, but the thing is already really heavy. But i'm not planning big big power anyways.

Killbill, the "camber by the hub", are your referring to the adjustable camber on the outer A arm mount? That is essentially what we have all been doing to our subframes for the last 15+ years here. There's actually been 3 different camber bracket kits made over the years, Raptor's was the last. It works, but only accounts for up to about 1.5 inchs of ride height variance. Depending on where you mount the bracket you can get that same range to compensate for a car thats been extremely lowered, but you will have to reclock the inner mounts too if you drop the mount low enough to compensate for the 1.5+ inch drops. Now the inner A arm mount and the stabilizing arm the FC runs is interesting! That would negate the need for re-clocking the inner mount, though I assume they did it to improve the inherent crap roll center trailing arms have. Anyways, like I said its pretty interesting, but it was blip in history, Mazda went full double wishbones 2 year later and never looked back (as should be, looking at you bastard mk5 supra). FD IRS...

 

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8" GX71 differentials do exist, if you really want one. I passed on one a few weeks ago that would have been CAD$1200 in my hand.

This morning, I bought this in rough shape:
https://www.rinkya.com/en/auction-s687347002

At $1200, the diff is still a small part of the cost to get it in the car. At $30, I'm sure there will be seals that cost more than the case. I guess we'll see what it looks like when it gets here.
 

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I got one a few months ago and Dean finally found one too. I'll be doing the swap this winter - looks like a bit of fab work will be required, probably moving a few mounting holes on the big diff crossmember(and custom CV shafts) but nothing major. I plan to rebuild it with a T2 Torsen from a FRS/BRZ and a 29 spline brand new 3.73 R&P rebuild kit from DM with a new input flange that also has a 66x66x11mm bolt up pattern (along with the smaller 60x60x10 that is the same as the truck diff big input flange for the 7.5). Then I can use a 1330 U joint at the back on the 66x66 pattern, and a DM 1350 slip yoke at the trans (that has removable ears so I can get the driveshaft out of the car without removing the diff) and a 1350 to 1330 crossover U joint at the front. Then the only part of the drivetrain left stock is the stub shafts in the control arms but they are pretty tough, not much chance of breaking one unless you are running a spool or welded diff!
 

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Yep yep, I already did a bunch of measuring and speccing out of parts etc. With a 29 spline brand new R&P, solid spacer, T2 Torsen, custom axle shafts, and a single piece driveshaft that has 1330 U joints on each end it should be pretty much indestructible in a mk2. The T2 torque bias ratio is around 2.5:1 so you can only ever get about 71% of the torque to one wheel, so I'm not worried about the stub shafts in the control arms so much, I've only ever seen them get broken with welded diffs and low gearing (4.30 or similar). The splines are pretty big.
 

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Discussion Starter #36
Very cool!

To continue the 8 inch diff swap talk, I was down at Junkie's garage last week (visiting the famous Satoshi\Rosso from the old days on this board!), and checking out Mike's crazy v12 and Darrow's awesome 2jzge vvti swaps (got to drive both :D). Naturally the talk turned to Crambo's crazy v12 conversion, 2jzs and big power and I filled them in your guys 8 inch diff adventures. I mentioned that the is300 diff is a really good way to go too if you are going to swap the entire IRS. Shawn brought up a good point, pulling axles on the is300 IRS is a pain. He used to pull them at Nix99 (long defunct wrecker in WA) and the nuts would strip when they come off. They would have to re-thread them after as they couldn't bolt back together after being removed. I did some research after that and it sounds like its the actual nut is a 1 time use part. Sounds like you have to buy new nuts every time you want to remove a half shaft on those IRS setups. Thats not a thing on the mk4 Supra, sc400, gs400 etc IRSs though. Anyways, not a deal breaker, but something to be aware of. I still think the IRS in the IS is the best choice these days in terms of design and availability, but I havn't thrown a subframe under a mk2 yet to see if its even feasible, just eyeballed them and confirmed it mounts similarly to the mk3 setup (which we know can be adapted).
 
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