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tranny confusion


Nismo280zEd

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This is more a nissan question than a Z question. I have a 78 280z and a 95 240sx both manual 5spds.

 

FS5W71C is noted as the 240sx manual tranny. Which is also used in nissan trucks, and z31, and maybe more applications. From what i gather... certain boxes use different ratios for 1-3 gear seems like 4th and 5th are usually the same. So my question is... becuase they are all noted as an FS5W71C does this mean all the internals are interchangeable?

 

Also... the Z31 is listed as using three trannys one of which is the FS5W71C now if it used this and two other trannys can i conclude they all have the same bolt pattern on the bellhousing? As I don't think nissan would make different Z31 blocks to accept the different trannies. Does this mean every FS5W71C has the same bolt pattern?

 

Help me out, i used the search feature and have gone crazy over google today but not a whole lot of info on swap ability and bolt patterns is out there.

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The countershaft in the transmission on the 280ZX trans doesn't have removeable gears. This means that you can't change the gears on the mainshaft, because the gears won't mesh with whatever is on the counter. Apparently some ITS racers figured out that there was a 3rd gear that was close enough to interchange from 2 of the 4 speed boxes even though the tooth count was different, but as a general rule that's a bad idea.

 

In all likelihood any attempt to change 1st, 2nd, 3rd, or 4th independently of the rest would not work. You can probably change all the gears on the mainshaft, and put in the corresponding countershaft, but at that point why not just get the whole other transmission???

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  • 6 months later...

Are all these tranny's the same? Is one better than the other?

 

FS5W71C:

- 86 to 88 200sx

- 89 to 96 240sx

- 84 to 89 300zx (non-turbo only)

- 87 to 89 Pathfinder (4-cyl only)

- 87 to 89 Van

Is Troy Armish Racing in Freemont, California (510-252-1001) the only company that can make the changes? Someone told me there was someone in Las Vegas or Arizona. Anyone know?

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These are not the same. As Jon pointed out, the early boxes do not have interchangable countershaft gears. Changing the mainshaft gears (with a fixed countershaft) is not a good idea as proper tooth mesh is vital for strength as well as noise reduction. That said, the gearboxes you mentioned are not the same dimensionally. Even very early, early and late S30/S31 5-speeds are incompatable with some internal components. The bellhousings are different (early bellhousing can be mounted to KA box with some work as the link provided will indicate). The shiter is in a different location too. Some gears can be interchanged from year to year. An example is the reverse idler gear in an 83 box which has 22 teeth. There is no replacement and Nissan offers a 21 tooth as a substitute. It does fit but there tends to be excessive noise for gear lash. The solution is to get a countershaft reverse gear from a 89 KA box and swap it in at the same time. The KA box uses the 21 tooth reverse idler gear so it is a perfect match. I learned this trying a variety of gears options to eliminate that noise. It only gets more confusing as the conversation goes on. If you go into http://www.carfiche.com and look at the a S30 transmission vs a 240SX transmission and you'll see subtle differences and part number changes. What exactly are you looking to do anyway?

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These are not the same. As Jon pointed out, the early boxes do not have interchangable countershaft gears. Changing the mainshaft gears (with a fixed countershaft) is not a good idea as proper tooth mesh is vital for strength as well as noise reduction. That said, the gearboxes you mentioned are not the same dimensionally. Even very early, early and late S30/S31 5-speeds are incompatable with some internal components. The bellhousings are different (early bellhousing can be mounted to KA box with some work as the link provided will indicate). The shiter is in a different location too. Some gears can be interchanged from year to year. An example is the reverse idler gear in an 83 box which has 22 teeth. There is no replacement and Nissan offers a 21 tooth as a substitute. It does fit but there tends to be excessive noise for gear lash. The solution is to get a countershaft reverse gear from a 89 KA box and swap it in at the same time. The KA box uses the 21 tooth reverse idler gear so it is a perfect match. I learned this trying a variety of gears options to eliminate that noise. It only gets more confusing as the conversation goes on. If you go into www.carfiche.com and look at the a S30 transmission vs a 240SX transmission and you'll see subtle differences and part number changes. What exactly are you looking to do anyway?

 

I'm building a 240z with an 83zxt engine. With mods, I want to produce around 350hp. My tranny goal is to have a strong / reliable transmission that can accomodate a short-shifter. So what is the right year 240sx that I should get the tranny from. I have access to two 89 240sx's now.

 

I was under the impression that I needed to take the FS5W71C from an 89-96 240sx. Once removed, I needed to have the bell housing modified and a new bearing installed. After that I thought it was a done deal. If I go this route, do I need the reverse idler gear?

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The 89 is fine. I have heard but not confirmed that a later 240SX box 'might' have a larger diameter output shaft for added strength. The bellhousing mods are all that's needed. Some swap the 240SX countershaft front bearing for the earlier smaller 280Z/280ZX bearing when installing the older bellhousing. That is okay. I will be machining my early bellhousing to accept the 240SX's larger CS bearing. The reverse gear was mentioned only to point out that some gears can be swapped to accommodate gearing changes if older components are needed but not available (no 22 tooth idler gear was available in my situation) or you are looking to modify the 1-4 gear ratios away from factory options. It had nothing directly to do with a 240SX transmission being fitted into a early Z such as in the link provided by Naviathan .

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  • 4 months later...
sorry this thread is kinda old but i was gonna ask if anyone knows if the mechanical speedo sender for the z works in the 240sx transmission so i can keep my stock speedo?? it looks like it fits in there but dunno if everything meshes correctly yet..

 

The speedo gear are larger in the SX box. Count the teeth of both gears. If they are the same count you're in business. If not, you should be able to get the required gear from Nissan for the later box. Two are immediately listed for the 240SX box 32743-35F20 (20 tooth) and 32743-35F21 (21 tooth). There may be others too.

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