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Is is possible to determine the final drive ratio of a Z differential without opening it up? Also, how to spot R180 vs. R200?

I have a 74 260Z with 4sp manual, which is driving like it has a 3.90:1, rather than the stock rear end. (That is, can I tell from the outside whether it is a 3.364:1 vs. a 3.90:1 by looking at it?) I want to put in a 5spd, but first I want to verify which rearend I have before I determine WHICH of the the three different Z 5spds I want to put in. Thanks.
 

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Re: How to I.D. which Differential & Ratio frm

From what I have heard, I do not know why people do not want to take the rear cover off and look. Please do not get me wrong, I was the same way until a couple weeks ago. I finally took the rear cover off to look at the ratio, it took five minutes to do, and the new gasket cost about $7 I think. I can understand the fluid issue, but changing it can not be bad for it. From what I know, that is the easiest and most positive way. I do not mean to be rude, but my suggestion, take the cover off and use white out to mark a tooth and start counting.
Good Luck,
Joshua L.
 

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Sorry, I now understand

I just realized why it is a pain in the butt. I had mine diff. out of the car, I was buying it from a guy. I forgot the mounting of it is from the back cover. Sorry about that. Well, I still think it would be easier and better to just remove the cover and everything else to count them. In this case, it may take 10 minutes.
Sorry,
Joshua L.
 

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Re: How to I.D. which Differential & Ratio frm

> Is is possible to determine the final drive
> ratio of a Z differential without opening it
> up? Also, how to spot R180 vs. R200?

> I have a 74 260Z with 4sp manual, which is
> driving like it has a 3.90:1, rather than
> the stock rear end. (That is, can I tell
> from the outside whether it is a 3.364:1 vs.
> a 3.90:1 by looking at it?) I want to put in
> a 5spd, but first I want to verify which
> rearend I have before I determine WHICH of
> the the three different Z 5spds I want to
> put in. Thanks.

Coop,
The R-180 has splined half shafts coming out of it. The R-200 has 4-bolt flanged half-shafts. That is the eaiest way to tell.
You can calculate the differential gearing on your car IF you know your tire diameter or circumference. For what it is worth though, if you have 195/70-14's and a 3.545:1 differential, your engine speed at 60 MPH should be about 3,000 RPM. With a 3.364 diff it would be about 2,850. With a 3.90 diff it would be about 3,300.
If you running taller or shorter tires it won't matter for determining gearing if you just read the speedometer vs the tach.
Hope this helps.
Phantom
 

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Re: How to I.D. which Differential & Ratio frm

> From what I have heard, I do not know why
> people do not want to take the rear cover
> off and look. Please do not get me wrong, I
> was the same way until a couple weeks ago. I
> finally took the rear cover off to look at
> the ratio, it took five minutes to do, and
> the new gasket cost about $7 I think. I can
> understand the fluid issue, but changing it
> can not be bad for it. From what I know,
> that is the easiest and most positive way. I
> do not mean to be rude, but my suggestion,
> take the cover off and use white out to mark
> a tooth and start counting.
> Good Luck,
> Joshua L.
Joshua, the gears are clearly stamped if you go to the trouble of pulling the cover off. ie: 39:10
for 3:90 ratio, etc.
I am fairly good at finding the ratio by locking up one side axle, and turning the driveline, but i would always pull the cover before selling it, if someone specified ratio, just to make sure. Joe
Joshua, call or type me on your 5 spd kit, we have them in stock, w, w/o syncros. Joe
 
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