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Discussion Starter #1
In my unsuccessful quest for an R-200 3:90 diff I need to know what color speedo gear and what years ZX they came in. Info I got states any ' 81-' 83 non turbo has 3:90 gears but all that I've seen had black speedo gear indicating 3:54. I haven't been able to determine ratios buy spinning the tire and counting revs of the driveshaft, reading my earlier post, I've been doing it wrong. I appreciate info on what color speedo gear and/or what year ZX has the 3:90 Thx
 

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Hi sportshooz-------------The 3:90 differential is found in all '81 to '83 280ZX's. The correct speedometer drive gear for this diff is the white one. Note that the '81 to '83 TURBO uses the 3:54 diff, with the black speedo drive gear. If you're finding a black drive gear in an n/a car, there has been a switch.

The best way to be sure of the diff ratio is to do a physical examination. Remove the rear cover plate and rotate the big ring gear until you can see the numbers stamped on it. The 3:54 diff should be stamped 39:11, the 3:90 should be stamped 39:10. Of course, this is a lot easier with the diff out of the car.

I wouldn't base too much on the color of the speedo drive gear. Over the years, many changes and modifications have been made to some of these vehicles, and there's no telling what has been swapped for what. Stick with the hard physical evidence, like the stamped numbers on the ring gear.FWIW

Roadman
 

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Agree w/Roadman

Just about any of the N/A's as he stated are 3.90.
The 3.70's are in 79's, but not 2+2 of that year.
A 2+2 has the lower ratio.
For some odd reason, I have two CV jointed 3.70 R200's out of ZX's, with the large turbo input flange, and I remember one came out of my 83 ZXT 2-seater, so maybe the 3.54 selection is a bit more restricted than just turbo (?).
I like the 3.7's myself, just because redline is just around 60mph in the top of second gear...
 

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Clarification

Roadman and Tony D are both correct, except neither of them clarified that the 3:90 rear ends came ONLY in the manual-trans N/A ZXs. The automatic cars had R-180 rears of some other ratio. So make sure your donor is a manual-trans, non-turbo ZX. Also, there is an excellent writeup on this with nice pics at the Datsun Z Garage (http://www.geocities.com/zgarage2001/z.html). Click on "Performance Tips" and go about 2/3 of the way down to find info on speedo gears and rear ends.
 

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Discussion Starter #5
Hmmm.....

I must have pulled 10 speedo gears..all black. I got my info from Bryan Little's web site as well .
81-83 n/a 2-seater 5 speed ZX
these nylon gears are really black..not stained white ones either (I know what yer thinkin')
Anyways I guess I gotta drop one and pull the cover, I would have done that to verify the diff after matching the color but at the yard, thats gonna be a pain
thanks for the responses. I'll let you know
 
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