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Thread: Gearbox modification - Z32/Z33 and RB25 on CA

  1. #1
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    Gearbox modification - Z32/Z33 and RB25 on CA

    I will try my best to explain the two methods i have been using to make Z32,Z33 and RB25 gearboxes fit CA and SR engines.

    The reason why i use Nissan gearboxes are because they use the same spline, so you can still use the same clutch.
    They have ratios that match the diff pretty well and they are cheap new.

    How much the input shaft sticks out over the flange is what is cruicial, the shafts are all the same but the amount of "stick out" is different.
    CA/SR = 18mm
    Z32/RB26 = 16mm
    Z33 = 12mm

    I aim to get the "stick out" same as it is stock on a SR/CA transmission.
    It`s better to have 1mm shorter shaft vs 1mm too long.

    For that reason i always make the housing a couple of mm too long before welding.
    Then i can machine it down to the correct length.

    For alignment it`s a good idea to bolt it to a block, vertically.
    There is also a cast seam on the top of the gearbox and the flange wich needs to match to get the orientation correct.

    Method number 1:


    This is how i did it on a RB25 gearbox:

    Ca flange over the RB housing:



    Cut the RB flange of:



    Machine the housing:



    Mount the finished machined CA flange to the centering device :



    Tack welding it:



    Finished welding and is going to be machined again (warps when welding):



    Finished:



    Mounted in car:




    Method number 2:

    This one is a little more advanced, its the same when cutting and machining the housing, but instead of welding on a flange from a donor box i use a blank watercut flange and machine the bolt-pattern and guides after the welding is done.
    The flanges are cut with a groove to match the cast seam on the gearbox.
    It`s a more accurate but also more complicated method.


    Here`s a photo of the watercut blank flanges, its made in pieces to save material and are bolted together to the guide plates shown.
    These bolt holes miss the stock bolt-pattern and is not used after welding.



    The "guide rod" wich centers the blank flange is shown here:



    Here`s a photo of some housings welded but not machined:



    Machining:



    Machined:





    I have probably missed several things, please feel free to ask.

    Also excuse the quality of the photos and all the SR realted photos, they are the ones i have the most pictures of.

  2. #2
    Guest ANDY black s13's Avatar
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    Nice bit of info there mate, this is something I have been looking into doing as my stock CA box wont like the power I intend to run
    I have spare CA blocks and gearbox's and I have a mate who can do the welding part very well, but he can't machine something as big as a bell housing
    so that part of the conversion will bump up the costs for me,so its become a back burner idea for the future
    respect to your skills and quality engineering

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    Quote Originally Posted by tommey View Post
    I will try my best to explain the two methods i have been using to make Z32,Z33 and RB25 gearboxes fit CA and SR engines.

    The reason why i use Nissan gearboxes are because they use the same spline, so you can still use the same clutch.
    They have ratios that match the diff pretty well and they are cheap new.

    How much the input shaft sticks out over the flange is what is cruicial, the shafts are all the same but the amount of "stick out" is different.
    CA/SR = 18mm
    Z32/RB26 = 16mm
    Z33 = 12mm

    I aim to get the "stick out" same as it is stock on a SR/CA transmission.
    It`s better to have 1mm shorter shaft vs 1mm too long.

    For that reason i always make the housing a couple of mm too long before welding.
    Then i can machine it down to the correct length.

    For alignment it`s a good idea to bolt it to a block, vertically.
    There is also a cast seam on the top of the gearbox and the flange wich needs to match to get the orientation correct.

    Method number 1:


    This is how i did it on a RB25 gearbox:

    Ca flange over the RB housing:



    Cut the RB flange of:



    Machine the housing:



    Mount the finished machined CA flange to the centering device :



    Tack welding it:



    Finished welding and is going to be machined again (warps when welding):



    Finished:



    Mounted in car:




    Method number 2:

    This one is a little more advanced, its the same when cutting and machining the housing, but instead of welding on a flange from a donor box i use a blank watercut flange and machine the bolt-pattern and guides after the welding is done.
    The flanges are cut with a groove to match the cast seam on the gearbox.
    It`s a more accurate but also more complicated method.


    Here`s a photo of the watercut blank flanges, its made in pieces to save material and are bolted together to the guide plates shown.
    These bolt holes miss the stock bolt-pattern and is not used after welding.



    The "guide rod" wich centers the blank flange is shown here:



    Here`s a photo of some housings welded but not machined:



    Machining:



    Machined:





    I have probably missed several things, please feel free to ask.

    Also excuse the quality of the photos and all the SR realted photos, they are the ones i have the most pictures of.
    Gday mate I know this is a few years down the track.lol.mad writeup and Info in this post mate,just wondering if u have the shaft lenght for rb25det box.im assuming it's the same as the z32 so 2mm shorter than SR, but can u confirm.im in Australia and looking for the info as blown another SR box and have a rb25 box I'm looking at to mod.cheers bud

  4. #4
    Guest Drifter's Avatar
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    Quote Originally Posted by silva4115 View Post
    Gday mate I know this is a few years down the track.lol.mad writeup and Info in this post mate,just wondering if u have the shaft lenght for rb25det box.im assuming it's the same as the z32 so 2mm shorter than SR, but can u confirm.im in Australia and looking for the info as blown another SR box and have a rb25 box I'm looking at to mod.cheers bud
    RB25 prop will be shorter than the Z32 from memory, the output from the box is not the same

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    Quote Originally Posted by Drifter View Post
    RB25 prop will be shorter than the Z32 from memory, the output from the box is not the same
    Cheers for the reply mate.i just spoke to a mate of a mate who measured his for me.its 12mm.i picked up an rd25 adaptor plate,mount and driveshaft for next to nothing so just trying to get everything worked out.with the 12mm adaptor plate and after machining say 10mm off bell housing (don't know whether i should take any more off than 10mm) it's still only gonna be 10mm shaft stick out.u reakon that's enough engagement into spigot. Is it ok to machine the the bell housing down more than 10mm or take some off housing and some off the adaptor plate aswell,,it's a steel adaptor plate so I'm guessing itd be fine losing afew mm. There's a couple of Companies that sell 11mm and 12mm adaptor plates and say u need no bell housing machining.dont get it
    Tia mate

  6. #6
    I <3 BBS LM Actual_Ben_Taylor's Avatar
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    Always got the option of an S15 flywheel to space the spigot out.

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    or bash an automatic spigot into the back of the crank and then a manual one into that. or fit a new spigot so its flush with the back of the crank and not slightly recessed like they come from the factory.
    dont forget that when you use an adapter plate you wont be using the OEM metal spacer plate so that will account for another 2mm or what ever the thickness is.

    ive an rb25 box hanging off the back of an sr20 using a 4 or 5mm thick steel adapter plate with no issues and none of the faces were machined.

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