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Thread: Gearbox - 18 to 25 spline 5 speed swap

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    Gearbox - 18 to 25 spline 5 speed swap

    G'day gents,

    My first real post on these forums...

    I need to replace my gearbox output shaft and am comparing all my options. A possibility is replacing my 18-spline gearbox/transfer for a 25-spline version. Is this a direct swap? Will I need new driveshafts or are they the same across all 5-speeds?

    Thanks,

    Will.

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    Twin Turbo verified Feedback Score 5 (100%) GTOJOE's Avatar
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    If you stay 5 speed you won't need to change drive shafts etc. What is wrong with it? cus might be cheaper to just change TC and use a 300m or quadco OS

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    Quote Originally Posted by GTOJOE View Post
    If you stay 5 speed you won't need to change drive shafts etc. What is wrong with it? cus might be cheaper to just change TC and use a 300m or quadco OS
    The main problem is twisted splines on my shaft. It will be cheaper just to replace the shaft, but having a spare tranny might be handy for future plans.

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    Twin Turbo verified Feedback Score 5 (100%) GTOJOE's Avatar
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    just change to a 300m shaft and new spools or a stainless TC from 3SX.

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    Forum User Feedback Score 0 Woodzy's Avatar
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    Just do what i did man, mine was trashed.
    Keep it 18 spline but get a strong 1, i got a quadoco from maximal performance, about $350
    New 18 spline TCs are on sale at 3sx, take the optortunaty for the $550...beef up what you want later, I just went for a Brace to keep it strongish for the time being.
    Seals set is about $80 from supercar engineering
    Gearbox Bearings are about $500 from either supercar or 3sx. Get the Syncros checked too, that could be the expensive part...I was lucky.
    Should be about $500 for labor (thats what is cost me) and your done with a beast that looks like this

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    Thanks guys,

    Yep, I'll be looking at a 300M or Quadco for sure. I've read a couple of threads on swapping output shafts *without* removing the transmission from the car. Not sure if I'd want to tackle that job myself though.
    One of those pre-built TCs would be nice from 3SX...

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    One day....it will be on 4 wheels. supporter Feedback Score 2 (100%)
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    would not touch a non SS or Billet TC also the 25 spline there is a greater number of so support in the future is going to be larger...so i'd go that direction too...up to you how much you want to spend on making it bullet proof though.
    Building a House, Car Mods on hold!
    1996 GTO, Owner since 2003.

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    hmm imo just get a 300m shaft, no one has managed to break either an 18 or 25 spline shaft yet so dont think it matters too much and not worth it if you have to go to all the trouble of converting the gb to a 25 spline as well as the tc. oh yeah the Quadco shafts are pretty sweet too, i'm making about 270awkw for the past 4 years launching at about 5k revs consistently, never had a prob with my big bearing 18spline tc with a rebuilt ouput shaft. Should be hitting about 350awkw soon so am going to be putting in a 300m shaft soon. Well I kinda lied, i blew up the tc but that was cos of an oil leak which lead to it completely eating itself.

    Maddy

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    Just for a heads up I've only got 1 18 spline quadco shaft left and it'll probably be a while before I get more.

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    Quote Originally Posted by Maximal View Post
    Just for a heads up I've only got 1 18 spline quadco shaft left and it'll probably be a while before I get more.
    Thanks for the heads up. About to send you a PM.

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