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Discussion Starter #1
Hello,

Long-time account holder here who lost his old account credentials.

I still have my 86.5 after 15 odd years and I am cannibalizing it to finish my race car. I am looking for a couple measurements on the differential if anyone has access to one. For what it's worth I used to contribute a lot to this forum.

Looking for:
-Total width from face to face where the cv shafts bolt to the stub axles (Just to be clear I am talking about the 6 bolt flanges)
-ROUGH distance from the driveshaft mating surface to the center line of the axles.

Any help would be greatly appreciated!

Cheers.
 

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Looking for:
-Total width from face to face where the cv shafts bolt to the stub axles (Just to be clear I am talking about the 6 bolt flanges)
-ROUGH distance from the driveshaft mating surface to the center line of the axles.

Any help would be greatly appreciated!

Cheers.
@Piratetip rebuilds diffs and is very knowledgeable. He might have the specs you're looking for.
 

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1987 Toyota Supra
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109 Posts
Hey there!

Trying to fit up another style diff?

I have a couple MKIII diffs lying around here being rebuild so. :)

Measurements:
Face to Face on the Diff Stub Shafts (width) = ~266mm
Face of Pinion Flange to Centerline of Stub Shafts = 273mm

Hope that helps!
 

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Discussion Starter #5
Hey there!

Trying to fit up another style diff?

I have a couple MKIII diffs lying around here being rebuild so. :)

Measurements:
Face to Face on the Diff Stub Shafts (width) = ~266mm
Face of Pinion Flange to Centerline of Stub Shafts = 273mm

Hope that helps!
Thank you very much!

The Miata I race is in dire need of a differential that is limited slip and not made of glass. The OEM Miata LSDs ones are hard to come by due to the popularity of the platform as a racecar. My old supra is just sitting there (rust got the better of it) and I remembered how stout the diffs are in those. A light bulb turned on and here we are. The supra axles are 6mm longer or so, and both have a bolt on inner axle stub. If the supra differential is narrow enough I can just make up adapter plates to bolt the small diameter 4 bolt miata axles to the supra stubs. With 150hp the diff will last forever.


Those measurements are exactly what I needed. I really appreciate your help. If the diff ever needs a rebuild I know who to bug for advice,haha!

Cheers
 

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1987 Toyota Supra
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Cool!

I hope it bolts up (with minor mods).
Sounds like a good idea to me, plus there are quite a few diff ratios to swap in.
Yes you are right that diff in a Miata will last forever. LOL
Very stout diffs we have in the MKIII. :)

What diameter ring gear does the Miata use?
Let me know if you need any other case measurements.
The MKIII is kind of a square brick shape. :)
Though... Now that I am looking at some photos of the Miata diff, that is too.
 

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Discussion Starter #7
The biggest difference is the Miata uses a large brace that runs from the engine to the differential called a "Power plant frame" That is easy to delete though and just use standard mounts.

The Miata uses a 6" ring gear. Light but fragile. Gear ratio is the same, 4.30. Thanks again! I'll post some pictures as I work my way through this.
 

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The biggest difference is the Miata uses a large brace that runs from the engine to the differential called a "Power plant frame" That is easy to delete though and just use standard mounts.
I like the idea of using the Supra diff in the Miata (we have a couple of each in the garage as well), but perhaps for a reason you might not have thought of, weight distribution. Miatas tend to be a bit nose heavy, although not nearly as bad as a Supra, which, in turn isn't horrible, just not ideal. Supra diffs are heavy in comparison, roughly 90 lbs if memory of building my car serves me well.

What sort of setup are you running in the Miata that you need such a strong diff though? I'd figure your transmission would be the weak point before the diff. If the Supra diff doesn't pan out for you, I know Getrag has a few options from GM applications that the LS swap crowd run.

As for deleting the PPF, wouldn't that reduce the structural rigidity a substantial amount? Guessing you're fully caged, from the "race car" mention, but still, every bit helps... Perhaps an adapter could be fabricated to retain the PPF?
 

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1987 Toyota Supra
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Thank you very much!

The Miata I race is in dire need of a differential that is limited slip and not made of glass. The OEM Miata LSDs ones are hard to come by due to the popularity of the platform as a racecar. My old supra is just sitting there (rust got the better of it) and I remembered how stout the diffs are in those. A light bulb turned on and here we are. The supra axles are 6mm longer or so, and both have a bolt on inner axle stub. If the supra differential is narrow enough I can just make up adapter plates to bolt the small diameter 4 bolt miata axles to the supra stubs. With 150hp the diff will last forever.


Those measurements are exactly what I needed. I really appreciate your help. If the diff ever needs a rebuild I know who to bug for advice,haha!

Cheers
Let me know if you need a set of the inner half of the Supra CV shafts.
A diff was shipped to me for rebuild but they left the inner CV's still bolted to the stub shafts.
Looks like they just took an acetylene torch and sliced the shaft in half.

Let me know if you want them, I have no use for em.
 

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Seems like a bit of over-kill to put the MkIII diff in that light of a car.
The 8" Toyota will take 1000 HP,
Yes, they are right up there around 90 pounds of cast iron.
Why not a diff from the FC3S ?
Besides, if your MkIII has a LSD in it, that is about the most shitty LSD out there.
Weak from the factory (speaking torque holding capacity), and just a true pain in the ass if you add 'up-grade' parts due to the design. It acts as a locked diff until it finally is overcome, then snaps loose.
Find an FC diff with the factory Torsen, and have about the best road race diff available.
It would probably take less to fit also.
 

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1987 Toyota Supra
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I've had no issues with the OEM clutch plate design when upgraded properly.
It has its limitations but overall it's a good design.
I have heard of the torsen carrier gears shattering under heavy load /abuse though.

What application/usage are you referring to where it destroys the clutch plate design? Also what modifications were done prior?
 

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First off, the shattered Torsen you heard about was on a car set up for drag racing, had slicks on it, with a really heavy clutch, on a drag strip.
Wrong app for a Torsen in the first place, under a heavy car with about 500 HP, and repeated clutch dumps on a sticky drag strip.
Shock loads are very high, and the car should have had a spool in it, instead of any LSD.
Even the best of parts have a limited number of shock loadings, and is why serious racers change out things like stub axles, half shafts, rings & pinions, even spools, and drive shafts after they have reached what there experience shows that the parts are reaching the breaking points.
So if not the diff, then the output shafts, half shafts or stub shafts will snap eventually.
But that diff would have never failed if on the street.

I have personally seen even the best LSDs eventually fail, such as ATS, Nismo, OS Giken, and Tomei shatter internal parts after they reach their life span. KAZZ is about the worst, and should be considered nothing more than a street diff for only mildly modified, hardly ever driven in anger cars.
I have imported a few thousands out of Japan, and have had to scrap or repair more diff than anyone on this forum ever touched.
the main problem with the A70 diff is it solely relies on spring pressure for it's holding ability.
The friction, once over come, releases suddenly due to the laws of physics, which is static friction is always higher than moving friction. That is why they pop, and snap when turning a tight corner.
When that happens on a road course, it causes traction loss mid corner, and just plain annoying when daily driving.
I have played with them many years ago, and had posted up here, or maybe over supramania the mods done way before Weir put their kits out.
Did you know that Toyota had heavier springs in them in the early years ?
They had to lighten up the spring pressure because of all the complaints about the 'noise' they made.
Somewhere, I think I even have the p/n for the original heavy spring. Never did run down the numbers for the dual spring they once tried.

Not saying the stock LSD, with a few improvements isn't a great street diff.
Going to a better design diff costs way more $$.
When people farm out the work, it's a real crap shoot on who is doing the work, and if the gear mesh, and bearing pre-load are ever set correctly.

By the way, I still have the custom shafts made up for checking break-away torque on the factory LSD, that I will never use again. One has a big flat plate on it to clamp in a vise, the other has a 1/2" socket welded to it for the torque wrench. PM me if your interested, I'll make you a hell of a deal on them.
 

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All good valid points.

Yeah I am aware of all the changes they made to the diff over the years.
I've gotten a few that have the LSD plate stackup mismatched as well as the weaker spring from the factory.
All the reductions in LSD performance at the factory for the drivers that didn't like the little bit of noise while cornering. LOL. Oh well.

I've lost track of how many rebuilds I have done now, guessing 40+.

I have yet to see one with a damaged LSD carrier from abuse or neglect from driving.
Of them all only 2 LSD carriers were unusable.
1. The carrier bearings spun the inner and outer races damaging the bore and inner shaft.
2. Someone had clearly been screwing around inside before me. They put the LSD together incorrectly and it shredded itself.

One thing on the LSD pressure though, it's not just the spring that locks up the plates.
The tooth profile of the spider and side gears are such that when they begin spinning against each other ( different wheel speed) they are forced to separate from each other. This also increases the load on the plate stackup.

I'm good on the side shafts.
I do enough of these rebuilds that I made my own set to measure breakaway torque.
And yes the rebuilds take a long time to get perfect, the good thing is I'm a perfectionist when it comes to this stuff.
Take my time and do it right.
:)
 
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