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Guess the transmission

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The trans on my 84 720 4x4 seems to have gone fubar the other night. I haven't got it pulled out yet but I decided to go to the pull and save to see if they had one before I get into the box. I found an 86 pickup I think was a D21 but couldn't tell cuz there wasn't much left. Even though I knew that the one I was getting had the longer tail housing I figured I might as well get it in case I need some gears and it was only $130. It has the newer shifter mechanism so I guess if it don't work for me at least I can rebuild it and sell. 

The tail shaft is marked as 5W71C, The bell housing is marked with ZL 71B #1 NMCA and the metal tag on the bell housing is marked 7Y20770. 

My guess is the previous owner combined the 2 cases in order to mount to his truck and have shorter shifting. 

Question are 1. what does the metal tag indicate? Is this a combined case and will I be able to use the gears if mine are bad?

Any info is greatly appreciated.


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Metal tag is the date of build plus serial number. Being a W71C, that means it was built in November 1987 and therefore is from a 1988 model year truck.


In general, W71C gears do not fit W71B boxes. W71C boxes, especially 2wd, grenade frequently, so if you got something decent to start with you should be able to make a good profit from it.


1986 was a cross over year for trucks as both the D21 (W71C) and the 720 (W71B) were made for the same year.


All of the above ASSUMES that this is the original transmission in that truck.


However, the numbers on the case suggest that you have a W71C gear train stuffed into a W71B case, in which case the tag number would mean built in November 1977 which is NOT possible for a genuine W71C transmission.

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Define 'fubar'. There are some things that can point to the transmission but are not. A bad clutch or low fluid in the clutch master. So what's it doing or not doing???



Both the late 720 and the early D21 used the same 4 cylinder Z24i engines so the front of the cases are essentially the same. If the D21 transmission is longer than your 720, you must have a 26" 71B called a shorty. The 71C is not going to be any good to you unless you shorten your drive shaft. 


The 71C transmission is extremely strong, twice as strong as the 71B and were used in the 300zx non turbo. If it grenaded it was abused.

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After getting it all taken apart it looks like the input shaft and counter gear got pretty chewed up. I opened up the one I got from the junkyard and it is not the same. The original has a 21/32 tooth set and the donor has a 22/31. 


In doing a pretty extensive search I have found replacements with the same tooth ratio for 86 and up. will this work? Nothing seems to be available for the original Trans. If the ones for 86 and up won't work is there another solution? Is there another trans I can put in my 4x4?

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21/32 is a wide ratio 4x4 transmission the 22/32 is a 2wd mid ratio transmission. As long as you change both gears as a set it will work. Unless you rock crawl you won't know the difference.


A 32/29 is a close ratio set used only on the 280zx after '79.

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Thanks datzenmike, I am very happy that I found this site. Seems you and alot of others are very helpful in the knowledge that you have. It will be very helpful now that I'm a 720 guy.

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On 11/13/2020 at 2:14 PM, azfiredog300 said:

Hey MMerlinn, I got the parts in today and I got to say that you are a life saver (or 720 saver). 




Thank you very much and I will most likely be needing other stuff as well so you are my first shot from now on.


Just remember, if it is not transmission or transfer case related, I DO NOT HAVE IT.

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