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trying to confirm some info on 280zx transmission ratios


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Posted this over on another forum but got no response so trying here.
I am replacing the stock 4 speed in my 72 510 race car.

After searching every conceivable thread on all the nooks and crannies on the net, I decided that the "Close ratio" 280ZX box was the best choice. I found a really nice looking 82 and bought it. I have verified that the ratios match the FSM for a "close ratio" box - 3.062/1.858/1.308/1/.745.

Next, following all of the vintage net wisdom, I tracked down a 32310-58S54 OD gearset (NOS still in the box!!) with the expectation that this would yield the road race perfect .864 OD ratio. This gear set is definitely 22/37. Oh boy - well on my way to faster lap times and the trick set up!!

Then I found this spreadsheet in a thread on another site -

Main C/G Ratio
23 29 0.793103448
1 34 14 3.062111801
2 28 19 1.85812357
3 28 27 1.307568438
4 1 1 1
5 26 44 0.745059289

I have confirmed that all of the tooth counts in this spreadsheet match the FSM and the ratios in my box.

When you plug in the magic 22/37 numbers into fifth - you get the same old .745 OD ratio, not the .864 that me (and every road racer) wants.

So.....it appears that all of the old net wisdom was wrong. The 32310-58S54 gearset does not yield an .864 OD in this tranny. It is possible that this 22/37 gearset got switched into the wrong box and the 32310 gearset is some other ratio, but that seems highly unlikely and there is no evidence of a different fifth gearset that actually yields .864 anywhere on the net.

So before I punt the whole thing, does any one see an error in the spreadsheet, the method, or my ability to count teeth on a gearset??

I know that you can change the main ratios with some other boxes and get a hybrid .709 "main" ratio and yes, you will get a .864 OD, but in the process, you lose the desiriable 1.858 "close" second. It looks much easier to just get an 86 200sx box, swap bell housings with an L box and get 3.321/1.9/1.308/1/.833

Guru's please confirm!!
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26/44 is 0.594


22/37 is 0.590 so you traded gear teeth but the over all ratio is almost the same.


Your input/counter is 29/23 or 1.26


1.26 X .594 = 0.748

1.26 X .590 = 0.743 virtually the same.


You cannot change the OD gears to get 0.864 well you could but you would need gears that had a ratio of around .685 to work with the 1.26 = 0.863 (close) A 34/50 gear would give you .68





The '83 and up 720 Cab Chassis option had a five speed with 3.321, 1.902, 1.308, 1.000 and 0.833


It was the November '84 up to June '86 S12 200sx that had the same as above but with 0.838 5th.




Best I can do at the moment.

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Thanks Mike


Well so much for the mystical 280ZX close ratio with a .864 OD.


Sounds like I need to to find that 11/84 to 6/86 s12 tranny. I believe that is a FS5W71B tranny with the better second gear synchro and the bigger main shaft bearing and the larger shift fork rod.


Any part or casting numbers or any other way to ID that particular Tranny?? Which shifter does this tranny have, the regular two tabs with a lever or the rectangular box one??


Then I would need an L series bell mouth modded to take the bigger shift shaft and larger bearing. I do not think you have to relieve the area around the main bearing for clearance or do you??


Thanks again

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Like I said I have the wide ratio Turbo 5 spd. I'll confirm the ratios but I think the one you want is for the CA20 engine not the CA18ET.


The change to the 62mm from the 56mm counter bearing was '85 and on.

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I was hoping mine was that one but very much suspect it's the wider one with lower 1st to get the revs up faster for the turbo.


You read my other post about the 720 Cab Chassis 5 speed? Identical gearing just a different front case bolt pattern??? The Cab/Chassis option was a Cab and chassis only (no box)  intended for commercial use or camper conversion. You might find one cheap.

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November '82 and on build date, making it an '83 model year. It was only used with the Z24 engine and was the only years a 5 speed was used in a Cab Chassis. The engine tag number starts with E for the Cab/Chassis option.

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