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1982 Datsun 720 "Heavy Duty"


MattC280Z

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Bought the truck for peanuts months ago. Just have one question, in the FSM i bought for it it shows the "Heavy Duty" as a seperate model, (I believed it to be just a fancy sticker they put on the long bed models) but upon further reading, the Heavy Duty model has its own section in the page that tells you your final drive, and gear rations. Now the only difference i can find based on that is the very steep 4.375 ratio rear end which even with the 5 speed from a 280Z I swapped into it only slightly helps the RPMs. What exactly does it mean that my truck is "Heavy Duty" ? is the suspension stiffer? the frame stronger? rear axle tougher? what?

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On the engine room data plate, check the rear axle type.  The numbers will give a rough idea of the actual rear gear ratio, it would say something like HF43 for a 4.375 rear end, whereas normally it would be 38. 

 

After I sold my 620, I found this one, knew it was 4 speed but had the spare 5 speed from a 280Z laying around and knew if I swapped the bell housings it would work. It wasn't until i paid $300 for it and got it home that I read the plate and saw the same "HF43" my 620 had, lol. i bought it in an attempt to have a gas saver as my 620 would get nothing more than 21 MPG. 

 

Is it not a dually? I always assumed that the "Heavy Duty" model was the dually But, a higher ratio (4.3 something vs. the 4.1 in my '86 "Deluxe") would make sense for towing purposes, although it must kill your MPG. 

No it has no indication of ever being one either, that is the strange thing, the only thing that seems different is the long bed, and rear axle ratio. I checked the mileage last time I filled up and its getting 25.2 MPG, which, concerning that rear end doesn't seem too bad. But I give credit to the towing abilities lol, my friends 96 Dodge Dakota blew its tranny about 15 miles from my house and I towed his ass to my place, hills and all, and didn't seem to mind it as much except on the steeper hills. :thumbup:

 

My one concern is that I think the L20B had a redline of like 7,000-8,000 RPMs correct? I never ran it that high but considering at cruising speed in 4th gear she was screaming at 4,000 RPMs didn't bother me because it was half of the tach lol. Whereas the Z22 in my 720 has a redline of 5,500 RPMs. Yes the OD keeps RPMs below that even going 80 MPH (which is kind of scary lol) but are those dangerous for the truck with that rear end? is it mean't to only tow and keep low speeds? I just want to keep it running good as a really like it.

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They didn't have the dually rear end till 1985ish, and the funnest thing is that it is rated at 1700lbs, while the H190 is rated for more weight.

The best mileage I have ever got is 23mpg with an L20b with 3.89 gears in the rear, I have also got 23mpg with my LZ23 with 4.37 gears in the rear, but I drive fast on the hiway(70/75mph), I just cannot drive 55mph, that is why I use my Datsun diesel trucks on trips, I get 27+mpg with them, I even got 36mpg once. :lol:

The rear gearing can be changed, you can get anything from 4.88 gears to 3.30 gears for the H190, but in the end it is mostly how you drive that gets you the high miles per gallon, if you drive fast like me, you not going to get good mileage, but you will get there sooner.

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They didn't have the dually rear end till 1985ish, and the funnest thing is that it is rated at 1700lbs, while the H190 is rated for more weight.

The best mileage I have ever got is 23mpg with an L20b with 3.89 gears in the rear, I have also got 23mpg with my LZ23 with 4.37 gears in the rear, but I drive fast on the hiway(70/75mph), I just cannot drive 55mph, that is why I use my Datsun diesel trucks on trips, I get 27+mpg with them, I even got 36mpg once. :lol:

The rear gearing can be changed, you can get anything from 4.88 gears to 3.30 gears for the H190, but in the end it is mostly how you drive that gets you the high miles per gallon, if you drive fast like me, you not going to get good mileage, but you will get there sooner.

I have just been using it for trips to class and work, 10 mile trip both ways. Not much around here but straight highways. I also tend to skip 4th and go straight to 5th, I've tried to look for a rearend to swap around here. i just found out recently the speedo is constantly 5 MPH fast. One if the other things about the rear end being so steep that I hate is when you let off the gas in gear it instantly begins to decelerate rapidly, even when I push the clutch in or in neutral it seems like that rear end just drags it down. On the contrary, 1st, 2nd, and 3rd gears are very quick from the start, lol.

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The '82 had a Z22 not an L20B so everything is in question here.

 

Look on the engine tag under the pass side hood hinge on the inner fender.   A true HD or Cab/Chassis model starts with an E as in EMLG 720 STV(or U) up to Oct '82 and ELG 720 WTV(or U)

 

E= Cab/Chassis

M=Z22 engine an H in this position is an L20B engine '80 only.

L= left hand drive

G= long wheelbase. there were no king cab or short wheelbase Cab/Chassis options.

 

W= dual rear wheels, only available from Nov '82 when the Z24 engine was introduced.

 

Up to Nov '82 only 4 speeds were used.

After (with the Z24 engine) only 5 speeds

Never an automatic or a diesel engine.

 

 

From July '81 on only a 4.375 differential was used.

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The '82 had a Z22 not an L20B so everything is in question here.

 

Look on the engine tag under the pass side hood hinge on the inner fender.   A true HD or Cab/Chassis model starts with an E as in EMLG 720 STV(or U) up to Oct '82 and ELG 720 WTV(or U)

 

E= Cab/Chassis

M=Z22 engine an H in this position is an L20B engine '80 only.

L= left hand drive

G= long wheelbase. there were no king cab or short wheelbase Cab/Chassis options.

 

W= dual rear wheels, only available from Nov '82 when the Z24 engine was introduced.

 

Up to Nov '82 only 4 speeds were used.

After (with the Z24 engine) only 5 speeds

Never an automatic or a diesel engine.

 

 

From July '81 on only a 4.375 differential was used.

I was just mentioning the L20B because my 720 has the same rear end (4.375) as the 620 I used to have. i swapped the 5 speed into the truck because the clutch was out and i had it lying around lol. So does Heavy Duty mean its just a cab chassis with a bed?

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  • 4 months later...

So since I have the "E" what does that make special about my truck? are the heavy duty models common? Whats on the truck that makes it different? Is it just a Cab/Chassis with a bed?

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Figured id make a build thread out of this because i have some plans for the truck and have gotten it running very reliably in the past couple of days. Heres pics I took the day I brought it home

IMG_2895_zpsydab4xks.jpg

IMG_2894_zpswfkvgi6v.jpg

 

Still even has the local Datsun dealer tag from the 70s and 80s on it lol

IMG_2897_zps4yjpncwg.jpg

 

And here is the magical Tag that gives my truck heavy duty status B)

IMG_2898_zpsbstssnx7.jpg

 

Hands down the worst body wise is the bed, speckled with pits and small holes on the sides.

IMG_2899_zpssnddirnf.jpg

 

Engine, Z22 looks like someone left the oil filler cap off while it was running and other than wasps nests galore under here seemed pretty tidy. Drained the piss yellow 15-20 year old fuel out of the tank and put on a new filter started but would only run when foot held throttle open. Put new plugs, wires, cap and rotor on it. Air filter next, this improved the running exponentially but still wouldn't idle under 1,700 RPMS (a guess because at this point i didn't have a tach.

IMG_2902_zpsxaruil3c.jpg

 

While I had the air filter off I painted the air filter housing the color i plan to paint the truck. Also Royal Purple was running high mileage oil on sale with a filter, and stickers too! so i figured some strong synthetic oil would clean the sludge thats built up over the years. Then i douched the engine bay and deleted all the smog equipment.

IMG_3401_zpskoa6wnpc.jpg

 

Will add more updates as they happen guys!

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When we did the transmission swap I noticed the rubber on the carrier bearing was toast. So to save some cash I just bought the rubber piece and pressed the old bearing into it and reinstalled. This gave me the guts to take her for a test drive. Aside from chirping comping front the drivetrain she was doing great! and then about 2 miles from my house i look back and see sparks flying out from underneath the truck nowhere to stop so i limped it to where i work which was nearby, and after inspecting, the old carrier bearing seized (the chirping) and got so hot it caught the rubber on fire which fell apart when the road wind blew it all over the place. Wasn't too bad but there was built up dead grass and sticks that caught fire too, right next to the fuel tank... 

 

But! no oil pressure light, no overheating, and other than very loud brakes and uneven braking, she did very good!

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Once I got home from work today I saw a box my dad had put on my bed... it was the gauge cluster I scored off of eBay a couple weeks ago! I didn't even realize until i opened it and removed the one in my truck to use the best of both clusters that the one I ordered has a trip meter on it! Did you have to pay extra or get the 4WD 720s to get that? or was it just for the DX models? new carrier bearing is on the way as well as brake pads and rotors. but I repainted the needles and used an electric drill and a lot of patience to get the odometer from 151,000 to 181,600 like my truck cluster had, also had some LEDs laying around. Just piddling at this point because until the bearing gets in I can't drive her. Heres how it turned out.

IMG_3398_zps3xehqpqk.jpg

IMG_3404_zpsm64dsbvh.jpg

 

 

All I need now is the clock! and ill have the complete gauge cluster!  B)

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Parts came in today! Rotors, pads, and some paint  :rofl: got the wheel off of the drivers side, and the rotor was eaten up very bad. Almost half an inch thick in some places.

IMG_3393_zpswl7pjbg0.jpg

 

Sorry about the Snapchat labels I take better Pictures through that lol. Here you can see the deep gouge in the rotor, I'm surest was rusted very badly and driving it those few miles rubbed the rust off and gouged it so bad.

IMG_3394_zps1dircjlh.jpg

 

Compared to the new,

IMG_3395_zpsm2bssrt9.jpg

 

And torqued down, installed.

IMG_3396_zpsjlz51r7a.jpg

 

My Radiator overflow can was brittle and I had tossed a tool or something into it and it cracked so I took it off and replaced it with something more, informal, but practical.

IMG_3403_zpsuxdynqbs.jpg

 

Looked on eBay and found a new one but its says its for an SD-22? are they different at all? mine completely disintigrated when it was in the sun and i tried to pick it up.

 

 

Did a trial run for the paint i want the truck to be on the hood, fell in love

IMG_3397_zpszvwwivqw.jpg

 

Then removed the bumper and front valence, and fenders as a whole and painted them, being sure to throw some 3M undercoating on the insides for rust prevention. clear coated, let it sit overnight and heres the result, I also put a new coat of black on the grille and silvered the horizontal marks on the grille. Im very happy with the result, new if the new carrier bearing would just come in!

IMG_3392_zps2etjsm7m.jpg

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  • 2 weeks later...

Quick question, my local junkyard has a few hardbodies, however most of them are 90s models with the KA24s in them, are the 90s hardbody differential incompatible with my rear end? i was looking around and although it looks similar to my truck I can't say for sure, i know my truck is an HF rear end but most of the hardbodies say HG. Any help is definitely appreciated, 

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If you held off you can swap D21 Hardbody calipers onto new vented rotors.

 

I wouldn't run synthetic in any Datsun even if new. It's tooooo slippery and intended for much newer tighter tollerance engines. If you find your engine arts leaking around old gaskets and seals, replace with Chevron Delo 400 or Shell Rotella T 15w 40  at the next oil change.. High ZDDP levels and is a diesel oil and highly detergent for engine cleaning.

 

 

The '79 620 had the first Cab/Chassis option though there was a camper option. It had single wheels. The early 720 also had the C/C and HD with sinngle wheels. If HD I doubt it came with duals only the later C/C

 

 

Redlne on the L20B is 7K the Z22 is just below 6,500. You will never ever hit that high in 4th or 5th so don't worry about this.

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http://www.infamousnissan.com/forum/archive/index.php/t-976.html

 

That link takes you to the list of axle codes and their translations.

 

I believe all trucks that have h190 axles can interchange diffs or ring/pinion/carriers as they have the same axle spline count.

 

Same with all trucks running a c200.

 

But h190 and c200 parts dont interchange.

 

Hf appears to be h190 axles.

 

Hg is h233 axle, definitely not a direct interchange, though perhaps you could swap the whole axle with a little work. Its going to be about 3 inches wider than your current axle however.

 

However they do have clsd and disc brake options available for them.

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http://www.infamousnissan.com/forum/archive/index.php/t-976.html

 

That link takes you to the list of axle codes and their translations.

 

I believe all trucks that have h190 axles can interchange diffs or ring/pinion/carriers as they have the same axle spline count.

 

Same with all trucks running a c200.

 

But h190 and c200 parts dont interchange.

 

Hf appears to be h190 axles.

 

Hg is h233 axle, definitely not a direct interchange, though perhaps you could swap the whole axle with a little work. Its going to be about 3 inches wider than your current axle however.

 

However they do have clsd and disc brake options available for them.

 

So according to that some frontiers have an HF190? awesome ill be on the lookout!

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If you held off you can swap D21 Hardbody calipers onto new vented rotors.

 

I wouldn't run synthetic in any Datsun even if new. It's tooooo slippery and intended for much newer tighter tollerance engines. If you find your engine arts leaking around old gaskets and seals, replace with Chevron Delo 400 or Shell Rotella T 15w 40  at the next oil change.. High ZDDP levels and is a diesel oil and highly detergent for engine cleaning.

 

 

The '79 620 had the first Cab/Chassis option though there was a camper option. It had single wheels. The early 720 also had the C/C and HD with sinngle wheels. If HD I doubt it came with duals only the later C/C

 

 

Redlne on the L20B is 7K the Z22 is just below 6,500. You will never ever hit that high in 4th or 5th so don't worry about this.

 

Is there much of a benefit to the D21 calipers? I find the truck stops fairly well. The engine hasn't leaked at all since the change, i remembered reading a post on here or somewhere that when the truck starts it chatters for about 2 seconds and it was a timing chain tensioner either broken or clogged up so i went with Royal purple to either clean out the cold or be slick enough to fix the sound. it went from 2 to 1 seconds in time before it stops but still does it.

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