How to put together a shortshaft 5 speed for a L20b

[wayno]

Ok, this is the first time I have tried to do something like this, so I might change things as I remember them. 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.

more to come

[MicroMachinery]

FINISH... THE FUCKING STORY... WHAT HAPPENED NEXT? ...WHAT ABOUT THE GLANDS?

[wayno]

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.

 

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

[wayno]

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. I am sure there are a few things I left out, I will add them as I remember them. wayno

[Jester]

Good stuff Wayno. Thanks for the write up.

[ggzilla]

Why not just use the factory short-tailshaft 5-speed? From 1977-1979 200SX (S10)? That car came with L20B.

[Laecaon]

Why not just use the factory short-tailshaft 5-speed? From 1977-1979 200SX (S10)? That car came with L20B.

 

My guess would be a better 5th gear, better Highway RPMs!

[yello620]

Why not just use the factory short-tailshaft 5-speed? From 1977-1979 200SX (S10)? That car came with L20B.

 

Cause those are the peice of @#$# Doglegs.

[datzenmike]

Overdrive on the dogleg is 15%. The 71B varies between 16% and 18% for the 2wd 720. The difference would be 'subtle'.

 

The biggest advantage with the short 720 5speed converted for use on an L series engine is availability. There are still lots of 720s laying around wile 200sx's are rare. The doglegs are usually well used, passed around or needing a rebuild. Almost equally important is the 71B tranny is stronger and intended for use in trucks and full size cars with L six cylinders.

 

 

Good stuff Wayno.

[wayno]

I agree with yello620, the dogleg is not a truck transmission, and I drive a truck, after going threw 3 of them in about 4 years, it got old, the last one seized on me, and the truck had to be flatbeded home, I was lucky I didn't have the trailer with me. When I put this transmission in my truck, it lasted at least 5 years before I got scared of messing it up, as it started to make a slight noise, so I pulled it and put the other one I have had sitting for at least 2 or 3 years waiting for this one to give up. I have not pulled the one I pulled out apart yet, as i do plan on rebuilding it(bearing & syncros), as it costs a lot to get one out of the u-pull-it yards these days, more than the rebuild kit. Doglegs are great car transmissions, if you use your truck like a car, great, put one in.

[KC Phirus]

A straight cut 2 speed.

 

 

 

 

 

 

 

do it

[wayno]

Overdrive on the dogleg is 15%. The 71B varies between 16% and 18% for the 2wd 720. The difference would be 'subtle'.

 

The biggest advantage with the short 720 5speed converted for use on an L series engine is availability. There are still lots of 720s laying around wile 200sx's are rare. The doglegs are usually well used, passed around or needing a rebuild. Almost equally important is the 71B tranny is stronger and intended for use in trucks and full size cars with L six cylinders.

 

 

Good stuff Wayno.

 

Thankyou datzenmike, I am convinced they are stronger myself, as I quit going threw trannys, even though the constant abuse continues. One of the funny things about all this is when I started building these kingcab 521s, and putting these shortshafts in them, I am finding that I have to lean forward to get it into 5th gear, so my next one will have a longshaft in it, and I will relocate the shifter hole, as the bucket seats are at least 6 inches farther back than the stock 521 bench seat, the other plus is that I drop these cabs onto 720 frames, so there is a lot more room down there, and the tranny mount cross member comes out of the 720 frame, that makes lots of room to get it out of there.

[EricJB]

Does anyone know the difference between a 620 trans and a Z car trans? Are they all 71B's? Are the bell housings the same, or does it have to be an 80 620 bell housing to do this swap?

 

Good stuff Wayno.

[poopypants720]

btw.... what kind of gear oil is that "slimer" green oil in the pics???

[wayno]

btw.... what kind of gear oil is that "slimer" green oil in the pics???

 

 

It's just gear oil, it was the normal yellow color, don't know why it looks green in the photos, and that is the color you want oil to be when you buy a used transmission, if it's silver, run away, if it's black, I would pull it apart and inspect it before I bought it, but some auto wrecking yards don't want to pull it apart, they just say it's good and has a warrenty/guarantee, but I want to know before I spend the time putting it in the truck.

I basicly try to buy from people I know anymore, or ratsun members with a good reputation, as I also have taken the time to pull a tranny in a wrecking yard only to find the case drilled after it was out, but I didn't buy it, I just bitched about the time I wasted pulling it.

[datzenmike]

Does anyone know the difference between a 620 trans and a Z car trans? Are they all 71B's? Are the bell housings the same, or does it have to be an 80 620 bell housing to do this swap?

 

Good stuff Wayno.

 

The '77-'78 are the same, the '79 truck has a wider ratio gear set in it . All are FS5W71Bs. The trucks may have extra external switches on them for emissions. I usually find the drain for the Z car transmissions on the right side, trucks on left. Otherwise identical.

[mklotz70]

.....so.....I didn't read every word, but to clarify......when swapping the lower bearing.....the ID of each bearing is the same? It's just the OD that's different, so either machine the case or swap the bearing? Is it easy enough to get the smaller OD bearing over the counter.....dealer? parts store? Maybe you could post up the correct name of the bearing and/or the part number. Cool swap!!!

[wayno]

.....so.....I didn't read every word, but to clarify......when swapping the lower bearing.....the ID of each bearing is the same? It's just the OD that's different, so either machine the case or swap the bearing? Is it easy enough to get the smaller OD bearing over the counter.....dealer? parts store? Maybe you could post up the correct name of the bearing and/or the part number. Cool swap!!!

 

Yes, the ID of the lower bearings(cluster gear) are to same, as it's basicly the same tranny, except the main shaft is shorter on the 85-86 shortshafts.

I go to what used to be called "bearings inc.", they measure it and ask me what quality I want(korean, jap, american), I usually go with one step under the best I can buy, but you can get them at "Baxters auto parts also(cheap).

I usually stay with the early L20b bearing(small one), until the front case lower cluster gear bearing hole gets screwed up, then I have the case bored out to the bigger bearing, and I then use the 85-86 front cover as it already is the correct size.

One thing to always keep in mind, if you ever run across a 720 diesel tranny that is bad, offer to buy the front cover(small bearing), as it is the only cover that is made of steel, the rest are aluminum, the transmission in my 521 diesel KC has the front case and steel cover bored out to the bigger bearing size as the case/cover was buggered up by the previous owner.

If you need any help, just let me know Mike, although I have no doubt you can figure it out yourself.

[EricJB]

A dozon or so years ago, I scored two L18's with 71b trans bolted to them. I used one of them for my recent 71b mutation, and it had steel shift forks and a steel front cover (small bearing).

Did they come on Z cars too? I dont thing it was from a diesel.

[mklotz70]

Great write up Wayne! I probably won't use the info anytime soon, but it will be here waiting when I need it :) Thanks!!

[wayno]

A dozon or so years ago, I scored two L18's with 71b trans bolted to them. I used one of them for my recent 71b mutation, and it had steel shift forks and a steel front cover (small bearing).

Did they come on Z cars too? I dont thing it was from a diesel.

 

 

Nissan made so many differant parts, it wouldn't surprize me at all that there were steel front bearing covers made for other apps, but I have only seen them on diesel transmissions so far.

Fact is I just focus on 720 transmissions, as they made mostly everything I have needed.

[jrock4224]

I personally would like to nominate both datzen mike and wayno for ratsuner of the year back to back consectuive years....awards to be given at canby yearly....

 

Ii spent friday building this tranny that i quized both mike and wayno about for a month or so.. i collected the parts but then sat on them as life does that sometimes... well i decided i want a 5sp...i went ahead with this combo swap...And omg this is one of the best swaps i ever made....even with a l16 its the funnest shit ever ..75 at 3200...granted down hill, with a tail wind....but she can hold her own in the fast lane anywhere...mmmmm i love it... so hees somethings i did when i did this... friday i cleaned the trans in the parts washer in the after noon after tthey dried i took apart both halves seperately and had it back together in about 30 minutes... seriously the cleaning took longer.... I used a three prong puller also heavily modified to pull the bearings they came off with no trouble.. swapped the bearing to the 720 5sp and was dropping them back together in no time....gave her some soul glow before i went home so we could throw her in in the am.....awww if it were only that simple...

 

 

 

 

 

reassembled...

 

 

 

 

 

 

took the morning to introduce the family to one another...first time truck had seen her big sis, and her cousin shrmmphy the blue two door...

 

 

 

 

ready to roll...day one..seeya tomorw for the same thing...haha

 

 

 

 

so swapping a tranny in a 521 and not removing the motor is a bitch, any tranny over the stock legth of a stock 4sp (26.5ish nches) is impossible....well i didi it twice...saturday we stripped everything, made a shortened (length only...important note..) mount and reinstalled with stock clutch throw out arm and bearing..mind u i removed the exahust to hang down .status left the torsion bars so space was limited...to do this we had to install tranny in hump then install clutch and pressure plate while tranny was up in the hole...its about 4 inches but with being able to rotate the motor on compresion helps ease the tightening of all the bolts...had to modify a snap on alignment tool to fit inside bell housing while tranny was in place but slld as far back as possible...and boom, yeah we are ready to slide together .. everything gets put back and we install the said shortened tranny cross member..(length only...important fact..) and install the splined hub with 40 mm freeze plug.....forget to install speedo cog once(important fact # 2...) stock drive line back in everything's good back off the stands ... supposed to be home hours ago so forgo the road test load up my shit and bone out ....start it up ... sounds like a tnak.... drive home on free way loving 70 mile an hour in a 521 ....pushing it.... yeah fun./.... get to a sdown hill push in clutch .....WHAAHAHAHAHAHAHAHAHAHA fucking old throw out coming unhinged... been noisey now its failing but it still works fine...second thing i noticed my feet were asleep from the vibrations....the tranny was riding against the flange for the shifter hole and that's the only place...l well shit ... sunday head back out for a 530 am meet in shelton at jesus's again.... new throw out(argh, the mounts easy the throw out was like step 2 in the swap....) in hand and we get it back in the air ... made a second (redid first) tranny mount... this time offsetting my mount a 1/2 inch lower as well as shorter..then i was back on the throw out... its so hard to remove a throw out while the tranny is in the truck ... we had it completely sideways in the hole and i was rotating the motor forward on its mounts as far as it would let me and it still barely went on and off....(never trust a throwout .. that's the hardest twenty dollar part install ever...)

 

any way everything went back together the second time as planned only faster...(u know cause we just did it the day before) forgot the tranny cog swap the second time.....(grrrr idiot...) got her all back together and its so freaking quiet ....no vibes runs perfect and almost no mods other than the tranny brace which i reccommend sitting lower it takes some grinding( iolator side we modified heavliy to avoid rubbing....basically just clearanced for the modified mount to fit inside the mount piece that attaches to tranny.. it fit originally but looked like twists or torque could cause a rub so i got over zealous with a grinder... smelled like the smokiest burnout for a while...... to make it fit but just the noise the starter made when the tranny was rubbing is worth doing to get rid of it...phixius knows what im talking about his truck does it... ( ps that mount is done when ever u feel like putting it on...)so other than my truck saying i am doing a buck O' 5 when i'm doing 75 this is great...(i will swap the cog tonight i think ... gotta adjust the slave too..) it has power but u gotta plan your passes with a l16...i will eventually swap a l20 in but i wanted to be able to freeway this truck and now i can safely and confdentally..

 

some one came by ....we caravaned back... but its name that ratsuner.....it was 5 sp 70 mph heaven...

 

 

thanks again wayno and d mike... these trannys are great and the parts are readily available...i used..

 

85 720 short tail 5 sp...

 

79 620 5sp bell housing...

 

all the stock shift fork and throw out from the l16 clutch and 4sp...works perfect and comes through the stock hole with the stock driveline...i have the stock 620 2 piece drive shaft i am shortenting to go one piece in this truck...just gotta find the material to attach the two halves of it with...apparently two piecers u experience more parasitic loss so i got maybe a half horse power i can reclaim....shoot if i got a electric fan we may be talking 3 hp unclaimed...man i could turn the heat on with that power....seriously this tranny is awesome...love the gearing

[mklotz70]

Very sweet! Makes me want to go pick up a couple of trannies just to do it. :)

[wayno]

At least I know now it isn't just my truck, it sure sucks having to remove and replace the clutch cover and disc just to get the tranny in and out of a 521, it adds a little time to the job, doesn't it.

I am also happy to know that a 620 front case can also be used, good info to know. :thumbup:

[Master-O-Turbonics]

Well I have been scared that my SD22 with long tail transmission was going to have SERIOUS shifter clearance issues with the bench seat in my 521 bodied early 720 4x4.... so I have found a later 720 4x4 stubby trans with its slightly longer driveshaft from a coworker of mine for $20.

 

The SD22 transmission is in great shape, so I plan on rebuilding the gear stack onto the 720 4x4 stubby output shaft with the stubby rear case into the SD22 transmission.