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720 4x4 leafsprings to lower your 521 or 620


fisch

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Allrighty, a few have wondered about using 720 4x4 leaf springs to lower their 521's and 620's. I'd love to see a pic of someone has tried it! So if you have it, post it!

 

I am curious what kind of drop you would gain. And how the ride would feel!

 

Datzenmike mentions 720 4x4 has 3.68" spring free arch and is stiffer. Normal for a 521 is 5" (620= 6.34"), so does that mean we'd get an extra aprox. 1.32" of drop for a 521 (and 2.66" for a 620!) by simply using 720 4x4 springs? Or would the softer 2wd spring-flex eat up some of that gain?

 

(This would also mean you 620 guys could get a free 1.34" of drop from using 521 springs. Again, unless it gets eaten up under load.)

 

 

 

 

In the mean time I thought I'd organize what info Mike has given us in one thread.

 

From King Rat Datzenmike:

 

"The 521, 620 and 720 leaf springs are the same length and width. 720 4X4 springs are stiffer than 2wd and have less arch."

 

"The 521/620/720 rear springs are all the same length at 1,200mm. 720 4X4 springs are mounted on top of the axle for added height so lots of arch isn't needed with them. All 4X4 spring packs have roughly 1/2 the amount of arch as 2wd springs."

 

"521, 620 and 720 springs are exactly the same length at 1,200mm.

 

PL 521

 

1,200x60x7 Qty two

1,200X60X6 Qty two

1,200X60X12 Qty one

 

Spring free arch.... 5"

 

'78 620 rear spring dimensions (in mm) all models.

1,200X60X7 Qty two

1,200X60X13 Qty one

Spring free arch....6.34"

(This is the same spring used on the '84 US 720 2wd)

 

The '84 Canadian 720 springs were stiffer:

1,200X60X7 Qty one

1,200X60X8 Qty one

1,200X60X12 Qty two

Spring free arch....5.20"

 

4X4 all '84

1,200X60X7 Qty one

1,200X60X8 Qty one

1,200X60X12 Qty one

Spring free arch....3.68"

 

I don't think this includes the big flat load carrying helper. "

 

Some inch conversions:

 

1,200mm = 47.2" length

60mm = 2.394" width

7mm = 0.275" thickness

6mm = 0.236"

12mm = 0.472"

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The 720, 620 and 521 leaf springs are the same 1,200mm length so they will bolt in. The 720 4x4 frame has the body mounts higher than the 2wd the springs can have less arch in them. To prevent bottoming out the springs are stiffer also. There is no exact formula for the drop you will get as the 4x4 springs may be slightly sagged to begin with? I think Chester put 720 4x4 springs in his 620....

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The 720, 620 and 521 leaf springs are the same 1,200mm length so they will bolt in. The 720 4x4 frame has the body mounts higher than the 2wd the springs can have less arch in them. To prevent bottoming out the springs are stiffer also. There is no exact formula for the drop you will get as the 4x4 springs may be slightly sagged to begin with? I think Chester put 720 4x4 springs in his 620....

 

 

Just so i'm clear on this, if I swap my 521 leaf springs & shackles with the 720 4x4 ones approx. how much lower will my 521 sit?

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Ok,i get that there is no exact formula. I was looking for an APPROXIMATE idea. If im going to buy a set ot these,unbolt them from the 720,unbolt my 521 leafs,etc.,then swap them in,I'd like to know if it's going to be enough of a benifit both in lowering,ride,& hauling capacity to be worth doing. I'm not looking for much more than a 3" drop. I will be semi -daily driving this truck over some pretty rough country & mountain roads.

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Ok,i get that there is no exact formula. I was looking for an APPROXIMATE idea. If im going to buy a set ot these,unbolt them from the 720,unbolt my 521 leafs,etc.,then swap them in,I'd like to know if it's going to be enough of a benifit both in lowering,ride,& hauling capacity to be worth doing. I'm not looking for much more than a 3" drop. I will be semi -daily driving this truck over some pretty rough country & mountain roads.

 

I heard it was about a 3 inch drop.

It's better to go this route with the 4X4 leafs, than using blocks, but that would be my opinion.  :)

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i was already on 3" blocks and added the 720 leafs.

i think i got about a 1.5" drop but def not 3"!!

i (as well as others) think that the springs are in fact softer.

check out this link for more info

http://community.ratsun.net/topic/57051-dawas-720-leaf-springs-into-620-swap/

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720 4x4 springs are able to carry more load than the stock 2wd. The spring rate is also higher. This probably translates to what everyone would call stiffer.

 

US 720 2wd (3 leaves)

Qty.

2 @ 7mm thick

1 @ 13mm thick

 

Free unloaded camber. The distance from the top of the top leaf up to the center line of the two shackle holes

6.34"

 

Spring constant (stiffness) 310.8 lbs/in.

 

 

 

US optional and Canada 720 2wd (4 leaves)

1 @ 7mm

1 @ 8mm

2 @ 12mm

 

Free camber........ 5.2"

 

Spring constant.... 442.4 lbs/in.

 

 

 

US and Canada 4x4

1 @ 7mm

1 @ 8mm

1 @ 12mm

 

Free camber............ 3.685"

 

Spring constant........548 lbs/in.

 

Although having similar number and thicknesses of leaves, the metals may be heat treated differently to get the different spring rates.

 

 

 

If lowering a vehicle it only makes sense to increase the spring rate. This will limit the suspension travel and reduce bottoming out on bumps. Could save you an exhaust system or damaged crossmember/oil pan/trans case on a raised manhole lid.

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So given what I just read, even putting the 4wd 720 leafs into a 2wd would lower the rear slightly (if at all) and give it a 100-200 lbs/in. higher spring rate, depending on what you have currently.. Thus making it a good idea to put in 4wd leafs regardless of what your doing with them.

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Stock springs work in the stock location at stock height but risk bottoming if lowered with blocks. 4x4 springs are lower and firmer, something that the stock springs are not. 4x4 truck springs are mounted above the axle and so are over 4" higher anyway.

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I think this is one of the better way to do this. The 720 spring is able to hold a heavier load so won't travel as far as the stock spring going over the same bump. Firmer is better on a lowered vehicle.

 

Never understood flipping a spring over. It fights the other springs and probably reduces the spring rate allowing the spring to sag under the weight to get the drop wanted.

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Oh it works for lowering, no doubt. I feel strongly that when lowering, you need stiffer springs to reduce bottoming out, a real possibility.  Reversing a spring not only removes it's spring rate from the pack but applies it downward in a negative direction. This would be similar to carrying several hunderd pounds in the back to lower your ride. Effectively the spring is softer? Not a good direction to go.

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The 520/521/620/720 rear leaf soprings are all the same length at 1,200mm (maybe the D21 too) I don't know the length of the 510 goon... might be the same length as the 610/710/A10 goons??? The truck spring may not fit but the lower leaves probably will. 

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My thought was,based on the discussion here about 720 4x4 springs being flatter,stiffer & such a good idea for a lowered truck,that the same concept might also apply to the truck style rear axle in my 510 wagon. It's my daily driver,i often have a carfull of the family in it,+ whatever else we bring along,& my tools/spare paets,etc. I'll be doing the 280zx strut/brakes swap,& buying some lowering blocks from joel. The whole flipping springs deal sounds like it's not the best approach,& I'm not building a race car so the mono-leaf spring idea isn't really necessary for me either. I have to get my 521 down from the p.o.'s place to whwre I can get to work on it,get it to daily driver status before I can do anything to my goon anyway,so I have a little time for research.

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I picked up the 720 4x4 leafs springs I bought today. The bushings look like they are pretty worn,& the shackles weren't with them. Can I use the 521 shackles,or do I need the ones from the 720 4x4? Does anyone know where I can get the bushings i'll need for this swap? We didn't list them at NAPA when I looked earlier today. I'll look again tomorrow.

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The truck spring (might) fit the goon. Likely they won't but there's nothing stopping you leaving the main top spring with the eyelets on the car and swapping in the lower leaves. There is a pin that located the spring pack to the axle perch. Probably rusted. I wrapped a chain around the spring 5-6 times and cut the pin off to release the leaves. Watch out!!! there may be a lot of stored energy when it lets go.

 

On my 710 I did this but only to add a flatter leaf to the pack. I had an extra set of 710 springs and trimmed one that was flatter and added it about the 2nd one up from the bottom. It didn't add to the height but makes it harder to bend them under load. I also added a 2" drop block at the same time. 

 

I used C clamps and vice grips to compress the pack enough to get a bolt in to hold them. I ground the head round so it would seat in the axle spring perch. Once the U bolts are tightened down it's safe.

 

Was five and now is six leaves.

710rearsuspension012Large.jpg

 

710rearsuspension011Large.jpg

 

710rearsuspension013Large.jpg

 

Not at all saying to use all the 720 leaves. That may be way too harsh. Use you best guess and add or subtract to suit.

.

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I went back to the salvage yard/tow yard that I got the 720 4x4 leafs from & got the shackles today. They're pretty bent,probably from someone hooking a cable,or chain to the shackle to pull the truck from being stuck somewhere. I either need straighten them or try to use the shackles on my 521 already. Will the 521.shackles work with 720 4x4 leaf springs?

I might try using truck springs my goon someday,but getting my 521 ready for daily driver status will come first.

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