Soopra / Truck / Mazda Hitachi rear end interchange question/idea

All right, throwing this out there because it's been gnawing on my brain for a while and I thought I'd ask before I scavenged boneyards to try to find stuff. Hokay, so, first off, I'm talking about the 3rd gen Supra here; the one with the 200mm ring gear. Now, it's my understanding that the diff can be fit into the truck 3rd member, which has umpteen ring and pinion options available for it for relatively cheap. What I'm wondering is if there's enough commonality in Hitachi made stuff that the truck 3rd member would fit into a 2nd gen RX-7 (the 86-91 squareish ones) with the turbo rear end (also a Hitachi made 200mm thingie) Using the scientific method of squinting at pictures of both, it looks like the carriers are similar, and the boltholes are in the right places but what are the actual odds that Hitachi kept the designs similar enough it would work? It would be nicer if the RX-7 diff could just take the truck guts but it can't; the pinion on the RX-7 diff is a lot longer and I don't think cutting and welding to the truck pinion would be a great idea. As a final touch, what spline are the Supra halfshafts, anyone know? The RX-7 ones are supposedly 31mm x 30 spline, and if they just plugged into the new hermaphrodite diff that would be lovely in a not-having-to-fuck-with-halfshafts way.

So, reader's digest version
1: Toyota truck 3rd member into Turbo 2 housing - odds of fitting?
2: Supra diff fit with Mazda axles?
3: (probably lower odds) Mazda diff bolting to Toyota ring and pinion and into Toyota 3rd member?
4: ...
5: profit?

It may be kind of a long shot but it would be possibly a lot less work than fabbing a mount for the whole Supra diff, and nice cheap truck R&P is a lot nicer than uberbucks custom Mazda R&P. For the record, I'm not asking anyone to go and make this for me, just on if the odds are good enough that I should bother scavenging bits to try it myself.

Trust me, I'm not like the others.

Even if everything else would interchange, the devious little bastards would change the ring gear bolt circle by 3mm. Or the same bolt circle but the number say 12 vs 10. or the output flange bolt circle, or the numbers there.

Nissan does that shot within same brand.
And on Nissans they do those very things between solid axle and IRS diffs.
the horror.
the horror.
the horror
Kill the brutes.
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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.



Edited 2 time(s). Last edit at 11/10/2011 11:14AM by john vanlandingham.

Well... how to put this... if I mention I have a mill, lathe and welder (and engineering degree but that might count against me) does it change the odds much, do you think? I mean, moving around the bolt holes or embiggening the hole in the diff housing are one thing, but if the centerline of the stubs would have to go through something that's metal on the RX-7 housing, that seems like maybe too much of a pain in the ass, unless a spacer or something would work.

Maybe I'm kinda crazy, but whether I can cheaply put 5.12 or 5.71 gears in a 2nd gen RX-7 is probably determining whether I'm building it or some other platform. I may have more time than sense, but there's limits, after all.

IIRC the RX-7 turbo rear is *not* Hitachi. It's not as strong as an R200, anyway.


Why reinvent the wheel? Pop in a Ford diff, or a stick axle.



Edited 1 time(s). Last edit at 11/10/2011 11:26AM by Pete.

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mekilljoydammit
Well... how to put this... if I mention I have a mill, lathe and welder (and engineering degree but that might count against me) does it change the odds much, do you think? I mean, moving around the bolt holes or embiggening the hole in the diff housing are one thing, but if the centerline of the stubs would have to go through something that's metal on the RX-7 housing, that seems like maybe too much of a pain in the ass, unless a spacer or something would work.

Maybe I'm kinda crazy, but whether I can cheaply put 5.12 or 5.71 gears in a 2nd gen RX-7 is probably determining whether I'm building it or some other platform. I may have more time than sense, but there's limits, after all.

Yes maybe the educational system that made you into an injur-near has made you forget that the simpleset solution is often the best solution.
And just cause you can doesn't mean you should.

A glaringly huge question staring in the face is : why not do as Xrattistas and now Dave Kern on the Bavarian Maggot Wagon do and use the whole stinking Supra diff? Then its just hooking up prop shaft, half-shafts and some simple mounts?

Is the potential ease of that the off-putting thing?

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Well, way I figger, if the shit fits together without too much screwing around, voila, no having to screw with fabbing shit to make the Supra diff bolt to the chassis (maybe even no screwing around with halfshafts if I'm way luckier than I deserve to be) which seems simpler than fabbing mounts.

Yeah, that's an "if" in there. If not, absolutely right John, just using the entire Supra diff is simpler. I even have one kicking around.

And Pete, reinventing the wheel... kind of is for simplicity in the rest of the car. I have a bunch of 1st gen shells sitting around, and obviously people rally those, but I've been paying attention to what people (I'm thinking of your here obviously) end up doing to them for reinforcement and getting the rear end to live and stick and whatnot. I know the 2nd gen subframe can swap in the front, and I know I can 3 or 4 link the rear end with a Volvo or Toyota or whatever stick axle... but it just seems so much less fucking around to use a 2nd gen. Xratties and I think that BMW and things use semi-trailing arms and crap so they can't be that fundamentally godawful, right? Or is that wishful thinking.

Incidentally, goddamn is it nice to have people willing to reality check shit like this.

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mekilljoydammit


Incidentally, goddamn is it nice to have people willing to reality check shit like this.

And it's good I can joke with you about Engineering school making people crazy. some people get REALLY pissed when i make fun of the cliched "injur-near" trip of way too complicated, too expensive for now percievable reasons---except maybe to show off "ex-spurtese".

But I betcha its a potential pisser-offer.

I think the second gen is a much better shell to start with if you are thinking rotary. Good brakes, decent steering, stiffer shell and easier to make really good.. Look at the rear towers though. Cut away the sheet metal that is in the way and is only speaker mounts.
Then measure from the trailing arm lower shock mount up to the car where the shock mounts and post it here. Do that so we know some idea of what length you can get in there or if it makes sense to raise the rear mounting point.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

There's more than a little reason it's cliche. Probably happens because almost all the classes are focused on how to make something that doesn't break and kill people and almost none on how to prevent the machinists and whatnot from wanting to kill the engineers. (possibly other reasons too, but I'm being charitableish) It's a bit different when the guy designing things and the guy making it without CNC crap is the same guy. "Goddammit, what ass put that in the bluepri... oh." And then there's what my grandpa called "engineers who've never touched a bolt"...

And yeah, some people have no sense of humor about it, go figger. But enough of that rant.

Very approximate measuring gives something in the 18-20 inch range between the lower shock mount and the upper. That's with weight on it too; it's sitting out in a field right at the moment and it's snowing out so I didn't want to fuck around with a jack and whatnot. More accurate I can get this weekend or something if you need it for these purposes.

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mekilljoydammit
And then there's what my grandpa called "engineers who've never touched a bolt"...

And yeah, some people have no sense of humor about it, go figger. But enough of that rant.

Very approximate measuring gives something in the 18-20 inch range between the lower shock mount and the upper. That's with weight on it too; it's sitting out in a field right at the moment and it's snowing out so I didn't want to fuck around with a jack and whatnot. More accurate I can get this weekend or something if you need it for these purposes.

Yeah my memory is that it is somewhat short and the shock I like to use is about 25" c-c and has 9" travel.. werry nice.
Yeah see if you or somebody can get us stock shock length.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

Cheating and using the Monroe site, they call the rears 22 inches fully extended and 14.5 inches fully compressed. Not sure that's 100% accurate either but the car's still not on the lift either. Quite a bit of room above the stock shock mounts to move everything up; just a matter of whacking a hole and grafting new sheetmetal going upwards or something, right?

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mekilljoydammit
Cheating and using the Monroe site, they call the rears 22 inches fully extended and 14.5 inches fully compressed. Not sure that's 100% accurate either but the car's still not on the lift either. Quite a bit of room above the stock shock mounts to move everything up; just a matter of whacking a hole and grafting new sheetmetal going upwards or something, right?

Yep, pretty damn simple.
A smrat guy would weld a couple of D shaped things on top and go to eyelet mounting and save over 100 bucks by not being forced to buy stainless shock pin mountings

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

That'd save from having to buy a spherical ball and shit up there (or make the stock mount work) for the pin mounts too, wouldn't it. Nice.

hmm. Someone as stoopid as me figgered how to put a toyletta diff in a mazdog rear subframe, and so far it hasn't even fallen out yet after one whole rallyx and nowhere near nuff of a rally afore something else broke so putting that soopra diff in yours shouldn't be all that hard to do compared with messing with boltspacing or splinecount or hermaphoditing parts or other such perversions.

Yeah, I had someone throw the engineer card at me the other day during a discussion..someone engineers toilet paper rolls, tampons and tooth picks. Big whoop when it comes to actually doing stuff with skin and knuckles involved, although knuckles might be involved with the tampon thing....

Hindenburg, Titanic, our own Narrows Bridge aka Galloping Gertie, Subarus first CVT, Olds quad4 head gaskets, Ford Triton spark plugs, Firestone tires, Mr.Coffee coffee makers, betamax...but hey no one remembers all that stuff.

http://www.thedailybeast.com/galleries/2011/04/27/20-most-useless-degrees.html. Number 8(with a bullet) (Remington bolt action self firing) no wait there we go again,

On the other hand someone engineered the Slinky which so far seems to be dead nuts reliable after all these years.

have you ever tangled a slinky though? its a nightmare