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Help identifying a transmission (added pics)


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Hello everyone. I wonder if any of you knows how to identify a transmission while it's installed. I have a 521 that came with a L20B and a 5-speed transmission from a 720. The transmission is leaking a bit from the speedometer pinion. That could be an easy fix, but I can't figure out what year/model was the transmission taken from, and I believe I need that info to get the right part. 


Per Charlie69 suggestion (thanksCharlie), I'm adding some pics (not very good ones) that maybe a Datsun guru can decipher. 


Thanks so much for you help!



Edited by Gabriel
added photos
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  • Gabriel changed the title to Help identifying a transmission (added pics)

Jack the truck up from the rear so transmission oil pools more to the front. Remove the speedometer cable and the 10mm nut that secures the pinion. It should be pulled straight out, don't twist it. I like to screw the cable back on loosely so you have something to grip. Oil shouldn't come out but have a pan ready to catch any.





The pinion sleeve has a large O ring. Unlikely it is leaking as it's very snug fit.  The pinion with the plastic gear is held in place with a roll pin. A suitable nail can be used to drive it out. The seal for it is flat sided. The large one you can just go down to NAPA and go through their box of O rings for a match. The little one? The part number is 32709-14600 maybe they can cross reference it to something. This seal was used in every Datsun from the mid '60s through into the '90s when they switched to speed sensors likely.



By the description an L20B and 5 speed from a 720 it can only be from a 1980. If it has a speedometer then it was a 2wd truck. They only came with FS5W71B 5 speeds and F4W71B 4 speeds.


Show the speedometer cable at the transmission. An '80 will have the 10mm bolt at the bottom 6 o'clock position.

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The more you learn the more you find out how hopelessly little you really know.


 Have a look for the 10mm speedometer pinion hold down bolt. If the transmission is an '80 or newer it will be at the bottom or 6 o'clock position.








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It's true. It's called Multiple Discovery in science. I'm not sure if it's the same case in philosophy. But I guess we're all driving around in life with more of less the same equipment and more or less on the same roads, so I guess we're bound to see the same landscapes. Know whatta I mean? 



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just to let you know you have a 510 type slave cylinder as the 521 comes out the front where the hose hooks up so it dont have to go around the torsion bar as that is not the stock set up.


I dont know if your hose is the stock 521 as most are a SAE threads.


I cant tell but looks like its kinked abit.


look up Tockauto for a photo. Im sure you can use your rod thats in the slave so it will wok(correct size)

Edited by banzai510(hainz)
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  • 2 weeks later...

The pinion lip seal & oring are available from Nissan.  You can ask for a 1980 720 with manual trans..........or ANY 77-83 Datsun 5speed application (except the 280ZX turbo with the T5 trans).  I buy most OEM parts from Lynchburg Nissan in VA..........Riley will know EXACTLY what you are asking for!

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