New World Datsuns...

I wrote this some time ago, I am not a writer, but will do the best I can.
This article is to explain how to make a heavy duty shortshaft 5 speed for a 510 or 521 that will have the shifter in the same position as it came stock with the 4 speed.
First you need the parts, you need a 1980 datsun 720 2 or 4 wheel drive front casing off a 4 or 5 speed longshaft transmission(31" long) with the front cover and the lower cluster gear bearing, it's best to have the whole tranny the first time. Then you need a 1985-86(84?) nissan 720 regularcab shortbox shortshaft 5 speed 2WD transmission(26" long), you need the 2 wheel drive for the speedo drive, but always check all the 4WD trucks in the wrecking yards in case they replaced it with a 2WD tranny. I start with the shortshaft to make sure it is good before I pull apart the longshaft. Side note, once you know how to do this, you can go to the "u pull it" yards, find one with both trannys, pull them apart, put together what you need and buy just the one tranny you need.

First you empty the tranny of fluids, then you remove the front bearing cover bolts, then tap the cover off from the side using the throwout bearing arm mount threw the arm access hole, don't hit it hard, just tap till it loosens.



Once you remove the cover you will see the two bearings, and have 5 bolts, one cover and a shim in your hands. In the photos below you can see the upper bearing with a ring clip holding it in position, that needs to be removed.



This is what you should have now.



Now you take the bolts out of the transmission case to separate the two halves.

Next you put a 2X4 on the floor and set the imput shaft on it holding the tailshaft steady, lightly tap around the base of the casing where it mounts to the engine, it is best I suppose to use a rubber hammer, but we use what we have, tap all around the bottom til the front case separates from the rear.



Now it is apart, you need to check this shortshaft transmission for excessive wear, missing teeth, ect.
You don't want to have to pull it out after you just installed because of bad gears.
More to come.

Once you separate the two halves, try to keep the tail housing in position, you might even put a nut & bolt threw one of the casing holes finger tight. generaly I just use the napZ case to hold the transmission now.

Next it is time to remove the lower clustergear bearing, I use a 3 armed puller that I have ground a little metal off the end of the arms so it will fit between the bearing and the gear behind it. This is what it looks like with the case removed.



Now put the puller on the lower bearing and pull it off, this bearing is to big for the 1980 case unless you have the hole machined out for this size bearing.



And this is what it should look like removed.

If the shortshaft gearing was good, no metal in the oil, no gear teeth missing or broken, then set this one aside and repeat pulling the 1980 case apart the same way, when you pull the front cover off, save the ring clip, shim, front cover, and the lower cluster gear bearing as this size bearing is what you need when putting it back together unless you have the 1980 case lower bearing hole machined out to fit the larger bearing, at this time I would buy a new bearing for the cluster gear.

Now it is time to put what you need back together, you need to carefully put the bearing needed on the lower shaft, I slowly tap it with a hammer till i get it started, then I use a small 2X4 and tap till I get to the shaft end, then I get the proper size socket and tap it home/till bottomed out. Next you put the 1980 L20b case on to the shortshaft transmission, I put the tailhousing into something that will hold the imput shaft upright, and I drop the 1980 case on to the bearings and shifter shafts, it will normally drop most the way by shaking and taping with my hands, but I have had to tap with a 2X4 in the past, once it bottoms out I put a couple bolts in to hold it there till I get the ring clip back into position on the main imput shaft bearing.





Once the ring clip is in position, turn the shafts and make sure nothing is binding, then replace all the bolts holding the two cases together.

Next put the proper front cover back on with the shim in the lower cluster gear bearing hole. If the case was not machined for a larger bearing then the 1980 front cover must be used with the shim, put the 5 bolts back in holding the cover.

You now have a short shaft 5 speed truck transmission that will fit a datsun 521 and have the shifter come out the stock shifter hole. This will also work with the 1981-86 SD22-25 diesel engines using the diesel front case. You might want to add a little sealer to the case before you put them back together.

Wow, great to see you ad this write up here wayno!
Its helped so many guys already. A++

Such good information.

can the mods make this a sticky, good transmission info. Thanks Wayno.

That doesn't need a sticky.
It will be stuck in the how-to forever.

I Need to get this done!! great work Wayno!

What rear ends have you ran with this transmission, Wayno?

How did you like the results with that/those gearsets?

flatcat19 wrote:What rear ends have you ran with this transmission, Wayno?

How did you like the results with that/those gearsets?

The work truck has 437 gears, and that will never change, as this truck hauls weight and a trailer daily.
The 521kingcab has 350 gears, it is my daily driver, it has a SD25 diesel engine with 71hp, but it has a lot of torque, enough to turn 350 gears when starting out, and it will do 80mph all day long on level ground, but I have to drop a gear on hills.
I think an L20b would struggle to get 350 gears moving even empty.
I am running 370 gears in the 1980 720 with a fresh SD22(61hp), it starts out fine, but the hiway is a struggle above 65mph.
It all depends on what you looking to do, most of our trucks will turn 390 gears, but will struggle when hauling real weight.

The point of this transmission is that it is a way better choice than a dogleg out of a 1977-79 200SX, and if you have a dogleg in your truck now, my hybrid transmission will bolt right in, as all the mods were made to install the dogleg already.

The main reason I wrote this is because the shortshaft shifter will come out the same shifter hole as the 4 speed, so it has no bench seat issues in a 521, and it is a heavy duty transmission in a light truck.