That is a later 720 truck 'shorty' 5 speed fitted with an L series front case to use with an L series engine. This transmission is 26" long, same as the 510 4 speed so no need to shorten the driveshaft.

That's a 20 tooth pinion. Try gently installing the speedometer pinion and sleeve upside down (180) from the intended. Don't force it. Put in gear and turn the input shaft and see if the pinion turns. Let me know and I'll X my fingers.

If this works I can show you how to modify the sleeve so it bolts in

Wagins 1

Posted March 19

Mike has you on the right track...

I originally did that with mine stumpy...

You can use the older speedo drive from the 63 series transmission they are the same length but you do have to rotate it 180 to engage and work....

Those stumpy transmission have a slightly different speedo drive vs what you have there.... i could never find one.. 

With the correct one the lock down tab is not separate.... 

The red gear is for any other 71b that's not the stumpy.... 

In '80 the sleeves were turned 180 and the mounting bolt moved to 6 from 12. Do idea why but the earlier sleeves won't work in the later transmissions. You can make them work if you turn the sleeve 180 and nick a new key way with an angle grinder.

To add some clarity for you....

What you have is mid 80s...

I think 84 85... maybe 86...

2 wheel drive 720 short tail transmission aka stumpy....

They were attached to a z series engine which is a different bolt pattern than the L series..... 

What is done is the front case is swapped with 1 bearing to fit an L series front case....

The red gear is not correct....

The picture Mike posted was just a reference picture for what you need to do with the black gear....

Are you trying to put a red gear in...

If so you need the longer bodies....

I see blue gears for the 720 on ebay with the lock down tab attached....

Those are the correct style, but they reference the transfer case.... 

The 4x4 had the speedo drive in the transfer case not the transmission like 2x4....

Or as stated you can use the older 63 series speedometer drive ( which is what the black one you have is) but it has to be rotated 180 and a new locking slot ground into it... ( Mike's reference pic)..

Hope that helps....

The pinion gear use depends on optional tire/rim and differential ratio of the vehicle it's going into. The 510 had a much smaller 23"? tire diameter and 3.90 the 720 was 25"-26" tire and 2wds anywhere from 3.90, 3.70, 3.545 and 3.364. For your 510 you want the same number of teeth as what was in the transmission in the 510. Probably 17 tooth for 3.90. That would be a Black pinion. A 20 tooth will turn 17.6% slower, or at 50 mph it will read 41 almost 9 mph low.

Hey look, it's Mike's "stumpy" finger!!  Charlie, once you decide on a pinion gear COLOR, let me know, as I have a few NOS gears.  I do not think I have the correct later pinion housing, but I will look later today!

Mike, you think he will need a BLACK gear?

TJ

That's my left middle finger. My left index finger was somewhat pinched in a printing press accident in another life so not suitable for a picture.

The OP shows a '72 wagon so if running original size tires and original differential and the speedometer is now correct then what ever pinion gear is in it, needs the same number of teeth in the pinion for the 5 speed. Have to take it out and look and see. My guess, and it's only a guess, is a black 17 tooth that's the most likely.

Mike, is there only ONE aluminum speedo pinion housing?  I have TWO, one is already "notched" to rotate, as you guys pointed out!  AND I have a 17t BLACK pinion!  So Charlie, watch the responses here & if it what you need, I've got!  I do have other pinion gears, so figure that out & I will see what other COLORS/tooth count I might have!

TJ

I think there were some steel 71B sleeves then all aluminum.

The tooth numbers range from 16 to at least 22. Obviously the worm gear inside remains the same so I always wondered how you could put more teeth on the same diameter plastic pinion gear... well you cant eventually the diameter becomes too large to fit against the worm gear drive. What Nissan did was have 2 (maybe 3?) sleeves with a different off set. The first sleeve is for 16, 17 and 18 tooth. All same diameter but larger and smaller teeth the worm can engage. The other sleeve is for 19, 20 and 21? tooth that is off set away from the work to allow the larger diameter pinion. Using a 16 tooth pinion in a 19, 20, 21 won't reach the worm gear. Likewise a 19 tooth in a 16 tooth sleeve will not insert or will crush the teeth. It's hard to explain but this is close to what happens.

My 70 has larger tires and a 4:11 differential. Speed was always reading too high. Last pinion I could find was a 21 and still about 2.5 - 3 mph fast at 50 and that's 2.5-3% at 100. Charley69 was kind enough to send me a 22 tooth and bingo!!!! perfect speedometer reading.  

Had to modify slightly and press in a pinion spindle. Above right is one of those steel pinions. Purple is 21 and Orange is 22.