720 springs on a 620

[dscottdatsun]

I got a set of 720 4x4 leaf springs for my 620 and I have a questions. To achieve the best function, do I purchase longer u botls or remove the bottom spring?

 

I see that the 720 springs have 4 leaves in the spring pack vs. the 620's 3 leaves. I also see the flatter arc for the 720's that gives the drop. But the 2 lower leaves look pretty hefty, does this make them too stiff or just right?

 

I am looking to lower it a little, still be able to carry a load and achieve a reasonable ride quality. I'm getting too old for a bone jarrin ride B)

[datzenmike]

Lets say you have a truck with 5" of ground clearance and you go over a bump to get in your driveway and your truck sags down 4" but misses the ground by 1". You lower the truck 2". Your ground clearance is now 3" but your suspension needs 4" of travel to get in your driveway.

 

Seems to me that if you increase the spring rate (stiffness) so the truck does not sag as much on a bump you could have the lowered look plus not hit the ground. The increased stiffness might be objectionable. Maybe try all the springs and take one out at a time till you get what you want. Removing a leaf will likely soften the spring and decrease the ground clearance.

[chester]

On my truck, I am running the full 720 4x4 leaf pack and 2 inch blocks. I can say that the 720 leafs are a little softer then the stock 620 ones. I am not sure how much weight you want to carry but with my setup I can carry about 400lbs but on bumps the rearend hits the frame. Hope this helps

[wayno]

I got a set of 720 4x4 leaf springs for my 620 and I have a questions. To achieve the best function, do I purchase longer u botls or remove the bottom spring?

 

I see that the 720 springs have 4 leaves in the spring pack vs. the 620's 3 leaves. I also see the flatter arc for the 720's that gives the drop. But the 2 lower leaves look pretty hefty, does this make them too stiff or just right?

 

I am looking to lower it a little, still be able to carry a load and achieve a reasonable ride quality. I'm getting too old for a bone jarrin ride B)

 

I am a little baffled, the 720 4X4 rear leaf springs have only 2 leafs and one lower strait short one, fact is all my 720 leaf sets have 2 main leafs.

All my 520/21 leaf sets have 4 leafs, getting progressively smaller, plus the strait lower one.

I have one 620 leaf set that originally had 3 leafs, but it was a dually motor home rearend, so a one full length extra was added which is a obvious addition.

So far the only 720 leaf set I have seen that had more than 2 leafs is the 1 ton version, which has a extra leaf that goes over the rear axle and hits the bump stop before the axle does, and it also has 2 lower strait ones instead of one.

Now I am not saying your leaf set isn't from a 720, I just never seen one before.

I would have to see the front eyelet on your rear leaf set to decide what I thought you have, as the 521 leaf sets have a permenet bushing in the eyelet that doesn't come out easily, all the other leaf sets have removable rubber bushings.

[wayno]

OK, I don't want to get any shit, so here are some oics.

This is a 720 one ton leaf set with extra over the axle overload, and the two strait ones on the bottom.

This is what the 720 eyelet looks like.

The upper leaf set is from a 520/21, it has four leafs, and a thick strait bottom one.

And this is what the 520/21 eyelet looks like, a sort of bushing.

[datzenmike]

Wayno you're right. The 720 uses less springs but they are likely thicker.

 

From the '84 720 FSM ....

 

USA standard had 2 x 7mm thick plus 1 X 13mm for (a total of 3 leaves).

USA optional were the same as Canadian standard and were 1X 7mm, 1 x 8mm, 2 x 12mm (for 4 leaves).

Canadian optional were 2 x 7mmand 1 x 13mm (for 3 leaves)

Heavy duty models were 2 x 8mm and 2 x 14mm (4 leaves)

4wd were 1 x 7mm, 1 x 8mm and 1 x 12mm (3 leaves)

 

From the '78 620 FSM....

 

Standard springs....... 2 x 7mm and 1 x 13mm (for 3 leaves)

Optional (camper) .... 2 x 8mm and 2 x 13mm (for 4 leaves)

 

 

 

Hope this helps.

[wayno]

Wayno you're right. The 720 uses less springs but they are likely thicker.

 

From the '84 720 FSM ....

 

USA standard had 2 x 7mm thick plus 1 X 13mm for (a total of 3 leaves).

USA optional were the same as Canadian standard and were 1X 7mm, 1 x 8mm, 2 x 12mm (for 4 leaves).

Canadian optional were 2 x 7mmand 1 x 13mm (for 3 leaves)

Heavy duty models were 2 x 8mm and 2 x 14mm (4 leaves)

4wd were 1 x 7mm, 1 x 8mm and 1 x 12mm (3 leaves)

 

From the '78 620 FSM....

 

Standard springs....... 2 x 7mm and 1 x 13mm (for 3 leaves)

Optional (camper) .... 2 x 8mm and 2 x 13mm (for 4 leaves)

 

 

 

Hope this helps.

 

They are absolutely thicker, and they all have about the same arc when laying on the ground, but when under the truck, the 720 leafs almost lay flat on that thick lower flat spring, the 521 springs also almost lay flat on that thick lower spring, but the closer to the eyelets the more upward arc there is in the 521 leaf.

All I can get photos of is 720 leafs under load, as all my trucks are on 720 frames, and I am trying to keep them low, the work truck isn't a good example, even though I am running 521 leafs on it, I have added two extra thick leafs to the leaf set, it has 6 leafs in it now, it takes a lot to get it to sink even 3 inches.

The most curious thing to me about lowering a vehicle is I would add more leafs to the pack, the more leafs there are, the closer to the frame I can get, I definately wouldn't be taking any out.

[chester]

Here are stock 620 leafs with 3 inch blocks This is 720 leafs with 3 inch blocks Both oics are with nothing in the bed. I was looking if I had a pic with the two leaf packs side by side but I do not. The biggest problem with running 3 inch blocks and 720 4x4 leafs, is that you only have about an inch from the rear end to the frame.

[wayno]

Here are stock 620 leafs with 3 inch blocks This is 720 leafs with 3 inch blocks Both oics are with nothing in the bed. I was looking if I had a pic with the two leaf packs side by side but I do not. The biggest problem with running 3 inch blocks and 720 4x4 leafs, is that you only have about an inch from the rear end to the frame.

 

 

You need to notch the frame now in the rear, but the biggest problem is the front, there is little one can do with the stock front suspension, you can take out the bump stops, but what we really need is a thicker/stronger torsion bar, that way one can be lower and still not bottom out.

What did you do to keep the upper balljoints from binding, did you flip the upper A arms?

What about the alingment, or are you just living with the tires being tilted?

[chester]

Well this is a king pin truck, so no ball joint problems. The bump stops were removed and sitting on bottomed out shocks. Since I wreck the truck in the pics. The new 77 kc will get a little notch and I will go back to three inch blocks. On the front so far all I have planned it raise the shock mounts. Not sure what else to do. I was thinking of trying to get some info on 720 torsion rods see if they will work and if they are bigger. The chamber wasn't bad after I replaced the upper control bushings. With the truck I have now I am going get everything done correctly for the most part. I don't want to ruin my tires when I get my 18s on.

[wayno]

Well this is a king pin truck, so no ball joint problems. The bump stops were removed and sitting on bottomed out shocks. Since I wreck the truck in the pics. The new 77 kc will get a little notch and I will go back to three inch blocks. On the front so far all I have planned it raise the shock mounts. Not sure what else to do. I was thinking of trying to get some info on 720 torsion rods see if they will work and if they are bigger. The chamber wasn't bad after I replaced the upper control bushings. With the truck I have now I am going get everything done correctly for the most part. I don't want to ruin my tires when I get my 18s on.

 

I keep forgeting that others are using the kingpin frontend.

Did you order a set of "Z'd" LCAs from Mike K?

That will get you at least 2 inches lower without messing with the torsion bar settings, and he might even be able to make a custom set that would allow you to get even lower, but there is a point when if you get a flat, you will lose control of the vehicle, as the frame will be dragging in the front, you don't want that to happen.

Is the 77 a balljoint front end, or is it still a kingpin setup?

[chester]

I look at the z'd control arms but I am not sure if I want to go that route. 77 is still king pin, 78 is when they switched to ball joint. I have thought of going to ball joint then use hardbody drop spindles. As of now I am just trying to get this new truck better road worthy.

[Zeusimo]

Here Ya Go

[wayno]

Here Ya Go

 

 

So what I think I see here is a 521 leaf with two of the leafs stripped off of it(the black one), the other leaf set is custom, or from some other manufacturer, as the eyelets are differant from how nissan normally makes theirs.

So what are they from?

[Zeusimo]

The Black One Is Stock 620

The Other One Is Stock 720 4X4

BTW.. They Use The Same Bushings

[chester]

The ugly looking leaf is the same thing as I have. I pulled mine off of a 84 or 85 4x4 720. Also I would like to throw in if you use the 720 shackles you can get energy suspension bushings and they work great. The difference with 620 and 720 shackles are the posts. On 620s they are bigger.

[Zeusimo]

Also If You Run Fatty Tires Your Tires Will Rubb Unless You Shave Those Weird Looking Springs

[metalmonkey47]

720 springs > blocks. No joke, it made a nice difference in the way the truck sits. Not to mention with 720 4x4 leafs, you can still go wayyyy lower easier.

[wayno]

The Black One Is Stock 620

The Other One Is Stock 720 4X4

BTW.. They Use The Same Bushings

 

So the black one is stock 620, is it 78+?

I wonder when they went to 2 leafs?

As for the other one, I have never seen eyelets like that on a 720, but I have not been looking either, the only 4X4 720 springs I have are 1980 4X4 leafs.

The only 620 leafs I have came from a 1979 datsun 620 dually mobile home, but that is what I was told, but it is obviously made differant than the spring you have pictured above, as it has 3 leafs, and the second leaf is as long as the main spring and wraps around the eyelet half way.

[Zeusimo]

Yup 78 620

And 84? 720

[wayno]

I learn more everyday, and now I shall be on the lookout for a set of them 4X4 springs, or just have a flat main one made with the eyelets turned upside down, that will drop it another inch at least.

[metalmonkey47]

The only issue I ran into with my 720 leafs was the destroyed bushings.

 

 

I'm using 521 shackles right now, and they use a different size bushing. FML. I just trimmed some heater hose and I'll work out bushings in a few days.

[Zeusimo]

Here's The PN For The 720 Bushings

[metalmonkey47]

I bought those, but my shackle bolts are still a larger outer diameter :confused:

 

Gotta measure them and drill them .

[Zeusimo]

You Could Have Just Got Some 720 Shackels