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My 620 flatbed!


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Hello all! I'm a new member to the forums but I've been here before with my previous datsuns. A couple weeks ago I picked up my 1979 Datsun 620 with a flatbed conversion here in Seattle WA. Not too sure if it's factory or if converted after market. Regardless the conversion seems to have been done very well and its very sturdy.


Things that have been done it:

-Weber 32/36 conversion

-Straight pipe with a cherry bomb exhaust (Need to get a better muffler as there is so much drone)

-Flatbed conversion with wood sides

-Previous owner had the head redone apparently


Here are some things I have done on it so far:


-Oil change

-New alternator with OEM spec 35 amp alternator

-New battery (550 CCA)



Things I need to do still:


-investigate the cause of some sort of leak in the rear of the oil pan gasket. (Prob just need to reseal the oil pan)

-Do a diff flush and reseal

-Tranny service with new fluids

-Timing chain tensioner possibly (Been hearing a lot of chatter on decel mainly)

-Brake rotors need to be resurfaced (front)

-Rear drum shoes prob need replacing soon too


I have attached what I ultimately want to do to the truck so hopefully I can follow through with it! haha


Thanks for reading!


This is what I want it to look like in some way shape or form. ⬇️ I do 3D modelling and renderings so I have been trying to visualize the end goal haha



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Flatbeds were not sold as such by Nissan however they did have a Cab/Chassis option that came without a bed for camper/motor home and commercial use. Any owner could have simply removed the old bed and made a flatbed for it. The Cab/Chassis option is designated as an EHL 620 on the '78 and '79 regular cab trucks. It may be on the driver's door tag along with the build date. Again it may just be home made.


I would advise you read up on the ZDDP controversy on line. ZDDP is a zinc anti scuff oil additive that has been slowly lowered to about half the level it was when your truck was new. Oil companies say it is reverse compatible for older engines but really it's because newer engines don't need it and it fouls the new catalytic converters. Our older cam on rocker valve train was designed to work with the old higher levels so makes sense to use the higher levels. You can run a 'racing' oil for flat tappet engines like SBC and SBF or simply do as I do and use a diesel oil such as Shell Rotella T4 which retains the over 1,100 PPM ZDDP levels. You engine won't fail from using today's oils, it's a slow process, but over time it will wear away out precious hard to replace valve trains. Do I trust the oil company's claims??? not one bit. All I have to do is reach for a different jug of oil. Rotella T4 comes in 10w30 and 15w40.

I would advise against using a synthetic engine oil. They tend to be so slippery that they pass through old gaskets and seals and leak. You will NEVER EVER need the extreme protection afforded by a synthetic oil.


For the transmission...

be sure you get GL 4 oil on the label or something that is copper brass alloy safe. Never GL-5. Again synthetic will usually leak past old seals.


For differential...

use only GL5. That differential looks ... ok. See how much oil comes out. If severely leaking look at the front by the U joint. There is a seal there that does not require you to remove the entire differential to fix. First I would power wash any old oil off and degrease it with a carburetor or brake cleaner. Change the oil and keep and eye on it to see if and where it begins leaking.


Timing chain...

will not ever chatter only on deceleration. The chain is simply turned by the engine and does not know when giving the gas or not. It may be simply quieter on deceleration and you can hear it easier is all. Chattering can also be a loose valve clearance adjustment and that is totally fixable.


The brake rotors...

can only be turned down a set amount so once off they may need replacing altogether so find a source first. If turning down may as well install new pads, why not?


Rear drum...

shoes are a visual check. Look for leaky wheel cylinders while in there and replace. Your brake performance is directly related to the rear shoes being properly adjusted also. Rear drums could probably be trued up also but again they are only allowed to be turned down so much and may need replacement. Find a source first just in case. Check the function of the emergency brake and get it working if not. It's not called the emergency brake for nothing. Constant use will keep it in perfect working order. Always park and apply the E brake.




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Wow! Thank you so much for all the useful information. When I reseal the oil pan I'll get the Shell Rotella T4 to fill it back up. For the differential, I have only visually looked at it and saw there was lot of gunk on it. So I'll clean it off with brake cleaner and observe for a little bit and see if its actually leaking or if its just dirt from the road.


Also, I noticed on the differential that the cover to open it up is on the front side of it. So the side facing the front of the truck. In order to dump all the current oil in there would I have to disconnect driveshaft to be able to get it cracked open? I'll dig deeper into the forums to see if someone already has a writeup for it, but I thought maybe if you had some extensive knowledge on it that might be even more helpful.

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I would power wash off first, maybe at a car wash?


See that little plug in the back? That's the fill hole. If in the future you want to check the oil level remove and you should be able to stick little finger in and touch it. Full is when you can't put more in. Do not attempt to force more in and overfill. Stick a 1/2" drive ratchet or Johnson bar in and turn to loosen. There is another on the bottom for draining. The top one will have a magnet on it to collect metal filings so take a look then clean it off so you can compare at the next change. Differential oil changes are 5 year 30,000 miles.

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Awesome! Thank you for the tips and helpful information! I didn't notice a drain plug from when I glanced down there. I must've looked at the wrong angle or  something haha. Seems like a simple job so I'll probably get that done next. 

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Had to do the timing chain tensioner years ago on my L20 she was real noisy!


Like the wood loading boards.  Going to make some folding ones for mine.


In Australia I believe the flat tray was a factory option.  Although a lot different to mine or this one lol.  Mostly used as farm utes here.

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22 hours ago, RyanC said:

Had to do the timing chain tensioner years ago on my L20 she was real noisy!


Like the wood loading boards.  Going to make some folding ones for mine.


In Australia I believe the flat tray was a factory option.  Although a lot different to mine or this one lol.  Mostly used as farm utes here.

Yeah I’m coming to think this was definitely done by a third party at some point. Thank you! 

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I think the 620 came to N Am without the rear bumpers on. As not fully assembled, they may have saved some sort of import tariff or something. Bumpers were installed by dealer? The '78 and up did have a Cab/Chassis option without the bed intended for camper/motor home or commercial use with custom work box. My '78 had a home made tray and I liked it. 

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Probably installed but the 620 covers 8 years. Refer to "The Chicken Tax" for ways around the 25% tariff imposed on import small trucks such as importing partially assembled vehicles and finishing them here.

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