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720 to 521 frame swap possible?


devilsnake98

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I was wondering if a 720 frame swap on a 521 is possible? Meaning putting a 521 body on a 2wd 720/ d21 hardbody frame. Any input/ experiences/ warnings would be appriciated. I can fab, that's not a problem, just was curious before I pulled the trigger and found a 720/ d21 donor for my 521.

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I was wondering if a 720 frame swap on a 521 is possible? Meaning putting a 521 body on a 2wd 720/ d21 hardbody frame. Any input/ experiences/ warnings would be appriciated. I can fab, that's not a problem, just was curious before I pulled the trigger and found a 720/ d21 donor for my 521.

 

Yes I have done it, but you are going to have an issue if you are going to use the stock box, the 720 regular cab wheel base is 101.4 inches, the 521 is 99.6 inches, so you are going to have almost 2 extra inches between the cab and box.

I actually made my 521 cab into a kingcab, and I used a 720 kingcab frame, and I used a stepside box, so all I had to do was extend my cab the proper amount and everything worked out.

The 620 regular cab frame is 101.4 inches, so that is only about 3/4 of an inch extra to deal with, so it might be a better choice, you can put all the front 720/hardbody brake parts on it.

I have done the 720 frame a few times now, it is the frame of my choice, as it has a power steering option, I like power steering.

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Ok, shortening the frame front to rear to get the proper wheel base is not a big problem for me to do, I'm really curious if the width on the 720 frame becomes an issue at all, if it's wider that is. I haven't got a chance to measure the width. And if and how much wider is the track width? Ie from drum to drum or wheel mount flange to wheel mount flange? Again anything helps and thanks already for the info wayno.

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Ok, shortening the frame front to rear to get the proper wheel base is not a big problem for me to do, I'm really curious if the width on the 720 frame becomes an issue at all, if it's wider that is. I haven't got a chance to measure the width. And if and how much wider is the track width? Ie from drum to drum or wheel mount flange to wheel mount flange? Again anything helps and thanks already for the info wayno.

 

The later 720s are wider then the early 720s, I don't actually know when they made them wider, I just know that an 86 rearend is wider than a 1980 rearend.

If you are going to lower it to the point that the front tires start to disappear behind the fenders, then an 86 frame is not going to work.

I am having no issues with my 81/82 720 diesel frame, and I can lower it some, maybe a lot, but to lower the front, I will have to notch the rear frame, as I only have a couple inches left in the back, and I would like to keep it level.

This is my 69 521 kingcab sitting on a 1982 datsun 720 kingcab diesel frame.

DSCN0077.JPG

 

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This frame is sitting stock height in the front, it has 3 inch lowering blocks in the rear.

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Yes I have done it, but you are going to have an issue if you are going to use the stock box, the 720 regular cab wheel base is 101.4 inches, the 521 is 99.6 inches, so you are going to have almost 2 extra inches between the cab and box.

I actually made my 521 cab into a kingcab, and I used a 720 kingcab frame, and I used a stepside box, so all I had to do was extend my cab the proper amount and everything worked out.

The 620 regular cab frame is 101.4 inches, so that is only about 3/4 of an inch extra to deal with, so it might be a better choice, you can put all the front 720/hardbody brake parts on it.

I have done the 720 frame a few times now, it is the frame of my choice, as it has a power steering option, I like power steering.

 

Wayno is this an advertisement for you doing custom kingcabs?  LOL

 

Wayno as with all your trucks this one is beautiful

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Sweet, that's what I was looking for, pics of a 521 actually on a 720 frame. I'm thing I may just go this route cause I can get a 720 2wd with a blown motor for next to nothing. Thanks again for the help.

 

If I were you, I would find a short wheel base 720, otherwise if you but a kingcab/long box 720 frame you will have to kingcab your cab about 10 inches, or lengthen your box about 10 inches, or have a flat bed.

I don't recommend shortening or lengthening the 720 frame, otherwise you will have to fabricate a different e-brake setup, as I did lengthen my 720, and the e-brake SUCKS!!!

Here is my 1980 kingcab/longbox diesel 720 towing the 521 when it was a 4X4 on a diesel 720 frame.

DSCN0314.jpg

 

I have found that the two front core support mount holes on the 720 frame are in the exact same place as the 521 front core support mount holes, so you line up them holes and the front wheels will be centered in the front fender wells, the other cab mount holes are off an inch or so, I made special mount blocks for the 521 kingcab, but the 520 project just got different mount holes in the cab, as they were close enough for me.

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  • 11 months later...

I have seen this thread somewhere on here... I am new to this site as of today so I will be posting a welcome thread in a bit of my 70 / 521 project,,, I decided to make mine a 4wd by putting the body on an 87 Nissan Pathfinder,,,, just started the project...love the posts, there is soooooo muvh good info on here!! Good luck with your project!

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Wayno, hypothetically speaking, if I mounted a 521 cab on a 720 reg cab frame, then the cab mount points would shift to line up with the 720 frame mount points? If I then made it a flatbed, the rest would be straightforward?

I just did this last month, I put a 1970 521 regular cab and box onto a 1985 Nissan 720 regular cab/box frame, the front two cab mounts under the radiator line up perfect, but the others need blocks modified to match the 720 frame cab mounts to the 521 mount points, mine look like this.

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DSCN4185.JPG

You have to make them to fit, I just didn't see a need for me to make these and offer them to people like I do the 521 tranny mount I make for 5 speeds.

Here is a link to the thread on the 1970 521 onto a 1985 regular cab/box frame.

http://www.nwdatsuns.com/viewtopic.php?f=24&t=1168

DSCN4065.JPG

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