Rear end gear ratio, and differential identification

[s14280zx]

I have a '79 280zx, and 2 parts cars, an automatic '82, and a '79 5-speed with a newer engine in it. I was wondering how I can determine what rear end gear ratio these cars have, and how to tell if they are R-180, or R-200 diffs. Is there a certain difference between them that you can see? Can I tell by the color of the speedo gear on the tranny? Did certain years have certain ones? Any help would be appreciated. I tried to search but couldn't find much.

[LanceM]

It's my understanding that all ZX cars had the r-200, considering the cars are together the speedo gears would be a good indication of the ratios.

This may help: http://www.geocities.com/inlinestroker/ratio.html

[FirstGenZ]

With the age of these cars and multiple owners, it's hard to tell whats been changed. As a rule the standard shift cars have a R200 and the automatic cars have the R180. The R180 diff has side seal retainers and the R200 does not. The retainers have five bolts holding them in place. The only way to know for sure what the ratios are is to remove the rear cover and check the numbers on the ring gear.

[=Enigma=]

It's my understanding that all ZX cars had the r-200, considering the cars are together the speedo gears would be a good indication of the ratios.

Actually I believe the 79s still had R180s except for the 2+2. In 1980 they all went to R200s.

Telling an R200 from an R180 is the easy part. They simply look different from the outside. The R180 has a rectangular shape and rear cover, then the R200 is more round and as such has a cover that appears more rounded than the R180.

As Lance said baove, assuming that the cars are all stock and the diff and tranny have not been previously swapped for something else, checking the color of the speedo gears would certainly be quicker that dropping the diff and cracking the cover. If a swap of either the diff or tranny was done at some point in the past, you have no way of knowing for sure without either cracking the diff cover open, or doing the spin/count method which can sometimes be difficult in a junkyard due to brakes freezing up.

Here's how the latter works according to Ross Corrigan , IZCC #255:

This will work with only one wheel off the ground.

http://zhome.com/ZCMnL/tech/WhatRearEndRatio.htm

If both wheels are off the ground use this method:

Jack up the rear end of the car supporting it on jack stands and make sure that the tranny is in neutral. Next, wrap a cable tie around the driveshaft and cut the excess to a reasonable length to act as a pointer. You could also just use chalk but I don't keep chalk around the house so....... Point the pointer or mark straight up or straight down at either the 12:00 or 6:00 o'clock position. Place a mark on a tire at either the 12:00 or 6:00 o'clock position. Now, turn the wheel exactly 1 revolution and count how many times the driveshaft turns noting the position of the cable tie pointer. If the cable tie made 3 revolutions and is at roughly the 3 o'clock position the ratio is 3.364 as in:

3 revs and ~3 o'clock - 3.364

3 revs and ~6 o'clock = 3.545

3 rev and ~9 o'clock = 3.70

3 revs and ~11 o'clock = 3.90

4 revs and ~1 o'clock = 4.11

It's not 100% accurate but it should get you close if done carefully.

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[s14280zx]

Thanks For The Help.

[texasz]

As stated above with the age of these cars there is no telling what has been replaced/swapped out so the best bet is a personal inspection. I completely agree with the removal of the rear diff cover and reading the numbers on the gears, this is by far the best and most accurate method...though there are others as mentioned above.

Also, as for the difference between the R180 and R200 take a look at this thread: http://www.classiczcars.com/forums/showthread.php?t=4270&highlight=r180+r200+difference

Then just for fun you may also want to read up on this thread as there is a ton of good information in it including a list of what diff came STOCK in which car: http://www.classiczcars.com/forums/showthread.php?t=1568&pp=15

Lastly, I just want to suggest that you use the search feature of this site as there is SOOOOO much great information here already and the majority of questions have already been asked and answered...repeatedly in many cases. I'm not coming down hard on you or anything just helping you learn about the site and Z cars...there's a wealth of information and help on this forum, in my opinion this is the best Z car site on the web!

[s14280zx]

This is the best Z-site around. I appreciate all the advice. I work on my 280zx whenever I get a chance, doing a little bit each day. I'm planning on having more time and money to work with next summer, so I'll use alot of this info and hopefully make one heck of a Z. THANKS.