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Transmission Gear Swapping


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If there end up being aftermarket gear sets let me know (and maybe I can save myself some effort)
This build is still in the planning stages. So I am asking now before I pull two transmissions apart.

Are there any differences in shaft diameter between the gear boxes, (or other differences for that matter) which would prevent me from swapping the 1st through 3rd from a F4W71B 4-speed to a later model 5-speed? (In short, are the gears compatible?)

If there is already a post on this I apologize. I could not find anything searching, and the search function kept breaking itself.

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  • 2 weeks later...

Answer is no. The 5 speed counter shaft has a long extension at the back of the intermediate plate that hangs all the 5th gear stuff. 1/2/3 gears are part of the counter shaft. Can't swap counter shafts between 4/5 speeds.


You "can" swap the 4th gear pair (B trans only) as they come off the shafts. 

You can swap 5th gear gears between 5 speeds.


Since the 4 gear pair ratio affects all the other ratio's you could mix and match a bit between 5 speeds to get some interesting ratio's. I have a truck 5 speed and a close ratio 83 zx 5 speed that if you put the close ratio 4th gear set in, you get these pretty interesting ratio's including a really nice high mileage overdrive.  


Here are the stock truck ratio's. Couldn't tell you exactly which year this is from, the bell housing is the rotated one that puts the engine vertical. Rest of it is pure 71B.



And here is what you get by swapping in the close ratio (CR) 4th gear set into that truck gear set.




I'm going to try this and see how it feels to drive. 


Here are the regular gaggle of 5 speed ratio's for comparison






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  • 4 weeks later...

Thank you very much! Of course the ones the previous owner wore out would be the ones I can't swap.


To answer the other question, easier yes. Cheaper no. I have two transmissions, and will be replacing the bearings and syncros come summer in the 5-speed. Unless someone who happens to be close by wants to trade me for my 4-speed, I would probably have to buy a whole 280zx to get another 5-speed.


The gear ratio change intrigues me, I will mull that over.

Edited by Oblithian
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