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Scrapson

Nap Z swap on an L20B

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I read on a forum already but it only mentioned just the transmission type I’ve been wanting to do a 5 speed swap and NAPZ transmissions are cheaper being in highschool and all. I had questions of do I have to get a new clutch throw out bearing and pressure plate or not besides the throw out bearing needing replaced. I know why swap a fine 4 speed but the 1st and 2nd gear are going out badly

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First, the clutch has zero to do with the transmission. You can replace it if needed but it has no idea what transmission is behind it and the transmission doesn't care what clutch is in front of it. 

 

Second you can't just swap a Z series transmission to an L series engine. The L series engine is leaning about 12 degrees to the right and the Z series about 6 degrees to the left. A Z series shifter will be tilted into the passenger's side.... if you could even get the rubber mount to twist 18 degrees!!! This is because the front cases of the transmissions are designed to orient the shifter properly. The thing to do is swap the L series four speed front case onto the Z series gears.

 

Notice the central case line up the middle? and the bolt hole that mounts it to the L series engine is close on the left side?

AaDPhXR.jpg

 

This is a Z series front case. Notice the closer bolt is on the right side now?

FkMQpJs.jpg

 

 

 

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Well crap alright. Is there any way around it? Like different bell housing or something? 

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read again...

 

11 hours ago, datzenmike said:

First, the clutch has zero to do with the transmission. You can replace it if needed but it has no idea what transmission is behind it and the transmission doesn't care what clutch is in front of it. 

 

Second you can't just swap a Z series transmission to an L series engine. The L series engine is leaning about 12 degrees to the right and the Z series about 6 degrees to the left. A Z series shifter will be tilted into the passenger's side.... if you could even get the rubber mount to twist 18 degrees!!! This is because the front cases of the transmissions are designed to orient the shifter properly. The thing to do is swap the L series four speed front case onto the Z series gears.

 

Notice the central case line up the middle? and the bolt hole that mounts it to the L series engine is close on the left side?

AaDPhXR.jpg

 

This is a Z series front case. Notice the closer bolt is on the right side now?

FkMQpJs.jpg

 

 

 

 

The 71B has a front case that covers the gears, a rear case and a steel adapter plate sandwiched in the middle that holds all the gears.

 

oEyImGv.jpg

 

tgkKO29.jpg

 

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I feel slightly retarded. So what do I have to do to swap a tranny then? Also how hard is it to swap bell housings and such?

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Don't worry we speak retarded here.

 

I'm at work right now but will find this post after work and elaborate what you have to do but the front case swap is basically a 12mm socket wrench small screw driver or snap ring pliers if you have them.  

 

Order the rear seal for the  transmission (only $5) There is a front seal (also about $5) you can access when swapping the front case so may as well do this one as well. Some lithium grease, 2 liters of GL-4 80w90 gear oil and Permatex Gray sealer. You may need to replace the counter bearing on the front of the gear set but this will be after the case comes off and it's examined. $12 but it's a high wear item. Get a new throw out bearing and change this while the transmission is out. ($15)This is one of those parts that is impossible to replace later without removing the transmission again. Always replace when easy to do so. 

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14 hours ago, Scrapson said:

I read on a forum already but it only mentioned just the transmission type I’ve been wanting to do a 5 speed swap and NAPZ transmissions are cheaper being in highschool and all. I had questions of do I have to get a new clutch throw out bearing and pressure plate or not besides the throw out bearing needing replaced. I know why swap a fine 4 speed but the 1st and 2nd gear are going out badly

Do you have the napz 5spd?

I believe a 79 620 have the long tail 71b...  it would be much simpler to just get a 5spd with the correct bellhousing....

A long tail 71b 5spd transmission should be cheap and easy to find....

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1 hour ago, Crashtd420 said:

Do you have the napz 5spd?

I believe a 79 620 have the long tail 71b...  it would be much simpler to just get a 5spd with the correct bellhousing....

A long tail 71b 5spd transmission should be cheap and easy to find....

I didn’t find a 71b 5 speed anywhere like market place near me or Craigslist. I thought they’d be easier to find but no. I’m sure it’ll be simpler and better to do but a NAPZ trans is $150 and I would like the economy since premium here is $4.46 a gallon since regular runs like shit. Ya know having a 5th gear and all

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1 hour ago, Scrapson said:

I didn’t find a 71b 5 speed anywhere like market place near me or Craigslist. I thought they’d be easier to find but no. I’m sure it’ll be simpler and better to do but a NAPZ trans is $150 and I would like the economy since premium here is $4.46 a gallon since regular runs like shit. Ya know having a 5th gear and all

Oh I know.... I just put a stumpy 71b 5 spd in my 521.... 

Well if you can get the napz for 150 it's still a 71b and you should have the correct bellhousing to use from your 4spd.... the housing swap isnt bad.... couple things to watch out for, but it is definitely do able.... 

Mike detailed the other things you'll need....

Good luck 

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Thanks I’m gonna need it I’m getting it this weekend from what it sounds like the guy is dropping it off. 

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First thing is drain it and see what comes out. Drain bung has a magnet on it. If ball bearings or large chunks stuck to it give it back. A black paste and fine metal dust is OK. Oil should be dark but clear. Milky send it back.

 

Fifth gear only helps out on the highway at cruise speeds. There's a very slight increase in mileage with an over drive. The '79 already has a 4.11 in it for mileage. 

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So I think the tranny is already empty but how else could I check it?

He seems to know quite a bit about these transmissions because hes got two types of NAPZ trans and he does have the actual 5 speed for an L20B but he wants $350 and being a broke high school student it's expensive.

 

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Well only a visual while swapping the front case. I guess you can turn the two front bearings by hand.

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Yeah Ill try doing that. This forum is the most useful thing besides banging gears to save a clutch. This pickup is my dream pickup and this forum is so useful for everything also its my senior project to graduate so with this tranny swap itll be over 60 hours into this turd within the 4 months Ive had it.

 

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There are a couple good write ups on here about the case swap with pics and tips.... 

One bit of advice take the tail housing off and reseal it too... you will most like break the bond anyhow when removing the front case.....

This will also allow you to visually inspect everything. Key point there are a couple nuts inside that should be checked and with the tailhousing off you'll be able to tell if the center bearings are good or not..... 

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o1doL87.jpg

 

If the transmission was drained the magnet was likely cleaned off so you won't be seeing this.

 

Disconnect your battery.

Take the rubber dust boot off push the E clip off the pin and push it sideways and out to loosen and remove the shifter.

i1OKBSS.jpg

 

Drain transmission, overnight is best.

Disconnect the driveshaft from the differential.

Unbolt the carrier bearing support and lift the two piece driveshaft away complete.

Disconnect the electrical harness from the transmission switches and secure out of the way.

Unscrew the speedometer cable from the pinion in the right rear side of the transmission and secure up out of the way.

Unbolt the clutch slave and secure out of the way. Save the push rod and secure the piston so it cannot fall out of the slave cylinder.

Unbolt the starter and pull forward out of the way. (THIS IS WHY THE BATTERY SHOULD BE DISCONNECTED!!!!!!)

Support the transmission and unbolt the transmission rubber mount and remove.

Unbolt the transmission cross member and remove.

Lower the rear of the transmission to open up some room to get at, and remove the 4 mounting bolts into the engine block.

 

There should be a sheet of steel (called an engine plate) sandwiched between the block and the transmission. There may be several small bolts through this and into the bottom half of the front of the transmission to keep road dirt off the back of the flywheel.

 

There may also be a steel or aluminum gussets on both sides of the block beside the oil pan and extending down and bolting into the bottom front of the transmission for support.

 

2ufhpNP.jpg

 

Wiggle the transmission up and down and it should split away from the engine.

Under the best of conditions the 71B is a prick to remove from a 620.

Slide to the rear so the front clears the pressure plate and by turning on it's side and wiggling around (and sacrificing a chicken) it will drop out of the truck.

 

 

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So I’m not going to be picking it up for a little while is there any way for me to visually inspect it without tearing into it to be able to know if it’s clapped or not?

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Not really. You could place it in all gears and turn the input while watching the output turn to check them. There are no moving parts on the outside to see.

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The guy I guess rebuilds datsun parts for a side job he’s got a shit load of parts like cranks and couple blocks if I recall correctly like 3 transmissions some other stuff but it’s pretty cool

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I usually get $100 + shipping for a later 1971-1978 240Z-280Z bellhousing (2pc trans case, you want the front half), but just sold my last one yesterday!  FYI the earlier 70-71 240Z has a 3pc trans case, so that bellhousing is NOT what you want!  I'm pretty sure I'm selling the 71-78 Z car bellhousings to guys doing the same thing..........using a NAPZ or an S13 240SX 5speed.  The 71-78 Z car bellhousing will BOLT ON to the NAPZ 5speed, then will bolt up to your L20B.....it is that easy.  There is machine shop work required on the 71-78 Z car bellhousing ONLY if you choose to use the later S13 240SX 5speed.  FYI if you need a clutch, buy the SAME APPLICATION CLUTCH that you already have, otherwise you would need to acquire other parts if you buy a different application clutch.  There are threads on how to identify the various clutches.  If you have a 77-79 620 & it has a 5speed, then it LIKELY uses the 77-79 620 L20B clutch.........so start there...........measure the disc diameter & if it matches what the catalogs say for the 77-79 620, then that should be what you have.  Hope that helps! 

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thanks. So I think my transmission is on its way out it’s making a very loud grinding noise constantly in 4th gear and slips in 2nd. I guess now is a good time for a tranny swap. 

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Side note do I have to shorten or lengthen my drive line because like I have seen and heard horror stories of drive lines becoming blue tooth drive lines it scared me shitless just felt all power kinda dip and behind us is a driveline going Mach holy shit ya know. I think it’ll be fine because it’s a short box but if not how do I do this

Edited by Scrapson

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Simple answer is get the same length transmission as what you have now... anything different would require a driveshaft mod....

Get under your truck and take a measurement.... 

It's either gonna be 26.3 or 31.5.....

I'm not overly familiar with the lengths but I believe most 71b transmissions are the 31.5.... i think the short was only 2 years in the 720... 

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2 hours ago, Scrapson said:

thanks. So I think my transmission is on its way out it’s making a very loud grinding noise constantly in 4th gear and slips in 2nd. I guess now is a good time for a tranny swap. 

 

Manual transmissions can't slip. If the engine revs up while driving then your clutch is slipping or wheels spinning.

 

48 minutes ago, Scrapson said:

Side note do I have to shorten or lengthen my drive line because like I have seen and heard horror stories of drive lines becoming blue tooth drive lines it scared me shitless just felt all power kinda dip and behind us is a driveline going Mach holy shit ya know. I think it’ll be fine because it’s a short box but if not how do I do this

 

This will depend on the 720 transmission, they can be long or short as mentioned. Have the seller measure the length. If 31.5" it will fit your 620.

 

I think only the KC or Long Bed 720s had the short 5 speed and this requires a special shorter console for the shifter hole. This console was used only on the '85 and '86. Could be wrong. 

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Alright, On occasion I have roasted tires from 1st to second trying to merge from dead stop to 55 my little brother was scared shitless when it grabbed traction. alright well I was told the clutch is relatively new like has 11,000 miles on it now but the previous owner treated it like crap because he cannot drive stick as I learnt when he went to drive it around. the clutch engages and disengages in the top inch I know some high end clutches like sport clutches do that.

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