Differential thatll fit on mk2 chassis, or mk3 diff and what do I need?

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  1. #1

    Differential thatll fit on mk2 chassis, or mk3 diff and what do I need?

    I tried searching but havent found what I'm looking to find exactly. I have a highly built 7mgte setup. Just wanting to modify the rear end. I highly doubt the stock will handle 600+hp. Was thinking about finding a mk3 differential and making a bracket to bolt it. What else all needs swapped if I did this? The shafts I would assume. Any new brackets needed, or spacers, etc? Hopeing to get this going within the next 2 months. Thanks in advance, Kevin.

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  3. #2
    CelicaSupra.com Member MrBubbles00482's Avatar
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    Any diff swap in these cars is a full on fab job. Ford 8.8 irs has been done a couple times.

    Most just get a detroit truetrac for higher HP applications for the stock housing.

    Past that you're going to have to worry about stub axles and half shafts. Someone had axles made not long ago but I wanna say they were 1k or more.

    Lots of info on here, just search
    1985 P-type "Elvira" Blue inside out.
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  4. #3
    CelicaSupra.com Member Funkycheeze's Avatar
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    Stock diff with truetrac and solid spacer will hold around 450 wheel ft-lb. (you will need a stronger trans and driveshaft, and a larger input flange on the diff from the 7.5" front of an old pickup or 4runner). And that is if you have the traction to put that much to the wheels. If you have a good ECM that can limit the boost pressure in the first gear or two that will help a lot, and will probably be necessary to maintain traction.

    Above that, you will need to replace the diff and axle shafts. I am working on integrating a GX71/MZ12 8" diff that has mk3 internals but similar mounting to a mk2 diff. Will need custom axle shafts of course as it has 6 bolt stubs, and they would be the next point of failure anyways.

    Using a T2 Torsen with a torque bias ratio is around 2.5:1 so you can only ever get about 71% of the torque to one wheel, and 3.73 or 3.90 rear gears, I wouldn't be as 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.

    I have found that the 450 to 475 WHP range (550 crank or so) is the functional limit of the mk2 chassis if you still want a car that is reasonable on the street or track. Above that it is either a poor drag car or just makes lots of tire smoke.
    Last edited by Funkycheeze; 10-16-2019 at 05:17 PM.
    '84 P-type, 5spd, Super red, black/grey leather - 2JZGTE swap, Precision 6262 on cast manifold, ECUmaster black with 875cc/min injectors, 465 WHP at 17 psi, built R154 with OS Giken twin plate, one piece driveshaft with 1310 joints, Truetrac with 3.73 R&P, 450 lb/in front coilovers, 300lb/in rear springs, Image BBM wheels 17x8 and 18x10, 4 corner BBK, AGX shocks, Whiteline bars, poly bushings, T3 GTX2 front control and steering arms etc. etc.

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  6. #4
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    There was an 8" version of the MkII/GX71 diff assembly in Japan, from when they first came out with the 1JZ.
    Very rare, and expensive when they do pop up in Japan.


    Seen people put the 8.8 Ford into them, and then promptly blow those up also.

    But another weak point is the stub shafts (what the wheel bolts to).
    This can be improved by removing the crush sleeve, and having a solid spacer made, just the same as a solid spacer in a diff makes it stronger.

  7. #5
    CelicaSupra.com Member Deanfun's Avatar
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    There's a GX71 8" differential on yahoo Japan right meow...
    Dean L.
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  8. #6
    CelicaSupra.com Member Funkycheeze's Avatar
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    That is exactly the diff I am talking about (and have). It is not quite bolt in (but close) and uses all 8 inch G code internals just like a mk3 (even the side shafts are the same).

    It was offered in the 6MGE MZ12 Soarer with 5 speed manual ONLY, and all GX71 MKII/Cresta/Chaser with 1GGTE. Some of the early ones have weird 4 bolt side shafts that have a slightly larger bolt center diameter than our 7.5" diff so the stock CV shafts still wouldn't fit. Best to get one with the 6 bolt side shafts (or get a set from a mk3 diff) in case you ever break one it will make a replacement easy to get, and it makes the adapter plates for custom CVs a lot easier as the custom CV will usually be 6 bolt as well so the holes are evenly offset.

    I'm looking at adapter plates at the diff and at the control arm to get me to a Porsche 930 joint that will be plenty strong. New weak point would be the control arm stubs, would need to model them in CAD and have new ones made from higher strength material, as well as a 6 bolt pattern. They are quite a bit bigger than the output stubs in the 7.5" diff (30mm spline OD vs 27mm).
    '84 P-type, 5spd, Super red, black/grey leather - 2JZGTE swap, Precision 6262 on cast manifold, ECUmaster black with 875cc/min injectors, 465 WHP at 17 psi, built R154 with OS Giken twin plate, one piece driveshaft with 1310 joints, Truetrac with 3.73 R&P, 450 lb/in front coilovers, 300lb/in rear springs, Image BBM wheels 17x8 and 18x10, 4 corner BBK, AGX shocks, Whiteline bars, poly bushings, T3 GTX2 front control and steering arms etc. etc.

  9. #7
    CelicaSupra.com Member SupraFiend's Avatar
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    Feel free to continue the conversation we've had going for the last year or so here...

    https://www.celicasupra.com/forums/s...Inch-Diff-Swap
    Black 86 mk2 Project Car
    New SDR 86 mk2 Daily User, Highway Cruiser AND Parking Lot Abuser in the works!

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