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Entire 720 front end swapped onto 521?


thisismatt

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I have a lead on a cheap 720, and I'm tossing around the idea of grafting the whole 720 front end onto the 521 to gain disc brakes and ball joint spindles. Besides the idea, I have no real clue of how feasible this may be. For whatever reason in my mind I don't feel that I want to swap cabs entirely (not to mention I think the 720 is a king cab). I've seen the threads on disc brake/ball joint swaps that involve a plethora of 620, 720, and D21 parts, plus custom upper arms, and that doesn't sound very appealing considering all the parts sourcing, T/C rod finagling, and still requiring upper arm fab. I would also be seeing what it would take to put in the 720 power steering.

 

Thoughts?

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i think i saw a thread on here someone put a 521 body on a 720 frame...i could be wrong and just dreaming this shit up lmao :lol:

No, you're right, people have...I just don't want to get too far away from stock bodied. I don't want to have to do a body lift or anything of the sort, or have a laundry list of other issues making things line up or appear stock, and maybe I wouldn't have to, but the threads I've read on cab swaps onto 720 frames didn't go into much detail, or like waynos was a way more custom king cab build that I don't want to do.
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Wayno has done a few of the 521 onto 720 frame swaps. Might look his threads up.

 

I personally would be doing a complete frame swap long before i would even consider grafting a frame together. Safer than a frame graft, i think so. Peace of mind, yes. I think it would be less work too. I have done a 620 cab swap in an full day, not a big deal.

 

Consider that the 720 frame is

1. ready for power steering if your donor truck didnt have it.

2. already setup for disc brakes. D21 upgrades are easy now.

3. probably already has better rear gears(ie. highway friendly).

4. rear shocks are orientated different than the 521, in a design that helps control axle wrap.

5. The fuel tank designed to fit the 720 frame has about 15 years less rust in it. :D OK,that is reaching a bit for it to be an advantage.

6. some say not to do a frame swap because of the vin number on the frame, but when you graft the 720 front clip on, you still lost your original vin and gained a vin from a 720.

7. Things like the worn rear leaf spring bushings have replacement parts available now.

 

Good Luck

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Wayno has done a few of the 521 onto 720 frame swaps. Might look his threads up.

 

I personally would be doing a complete frame swap long before i would even consider grafting a frame together. Safer than a frame graft, i think so. Peace of mind, yes. I think it would be less work too. I have done a 620 cab swap in an full day, not a big deal.

 

Consider that the 720 frame is

1. ready for power steering if your donor truck didnt have it.

2. already setup for disc brakes. D21 upgrades are easy now.

3. probably already has better rear gears(ie. highway friendly).

4. rear shocks are orientated different than the 521, in a design that helps control axle wrap.

5. The fuel tank designed to fit the 720 frame has about 15 years less rust in it. :D OK,that is reaching a bit for it to be an advantage.

6. some say not to do a frame swap because of the vin number on the frame, but when you graft the 720 front clip on, you still lost your original vin and gained a vin from a 720.

7. Things like the worn rear leaf spring bushings have replacement parts available now.

 

Good Luck

I was thinking more of a crossmember, t/c rod mount, and suspension mount swap, not frame grafting. The end goal would be coilovers as well, so a bit more fab there too.
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I would talk to Sycloned916, he has what your talking about in his 520, except he still has the kingpins, check the first page of his 520 thread.

Yeah, I saw his build - it looks like he stayed stock and added disc brake brackets and coilovers. I'd like to go the extra and get ball joint spindles, too! :)
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The ball joints require modifacations, and I don't beleave that the lower arm bushing is replaceable by the homeowner/mechanic, that leaves washers to take up the slop as the alternitive, that is not something I am willing to do, although it is probably safe. You will also need to buy a set of custom upper arms, unless you make them on your own like I did, I put mine together before I found ratsun.

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The ball joints require modifacations, and I don't beleave that the lower arm bushing is replaceable by the homeowner/mechanic, that leaves washers to take up the slop as the alternitive, that is not something I am willing to do, although it is probably safe. You will also need to buy a set of custom upper arms, unless you make them on your own like I did, I put mine together before I found ratsun.

I'm hoping by grafting the entire 720 suspension mounts to the 521 that I wouldn't need to, but perhaps I would if going with coilovers. I don't know about the bushing...you may be right. Maybe I just need to get the spindles and fab new arms from scratch :)
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They are two totally differant setups, i don't even think the 720 struts will fit in the 521 frame. I used the 620 hardware from the bushing(including the lower bushing) to the upper ball joint, and then I made an upper set of A frame arms from two sets of 720 arms. I would do it sycloned916s way and keep the kingpins, or transfer the cab to a 620 or 720 frame. It took me over two years to get it right, it did not just go together smoothly.

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I would go with a 720 frame. The KC cab mounts are the same as the reg cab. (at least 620 /720 are, don't know abut 521) ... but you would need a reg cab 720 for the cab and box to line up with the wheel opening. Rear gears are dependent on year/model 720 used. Gas tank mounts to frame and is generally larger. Steering components are mounted to the outside of the frame rails so there is more room beside the engine for alternator.

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I'm hoping by grafting the entire 720 suspension mounts to the 521 that I wouldn't need to, but perhaps I would if going with coilovers. I don't know about the bushing...you may be right. Maybe I just need to get the spindles and fab new arms from scratch :)

 

All that cutting off of brackets and stuff and then re-welding, I would just build new upper a-arms and source the leftover parts you need to get the 720 lower control arms to work. Don't have to pull any body parts that way.

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