Adding a leaf helper spring in a stock 79' 620

[rjgilligan]

With a full load in the back the springs lay flat, almost bending the other way. Has anyone used a helper spring on these?

 

This, in particular:

 

http://www.rockauto.com/catalog/moreinfo.php?pk=1133186&cc=1210150

 

Is this a bolt on item, or am I going to have problems with my shocks? I just bought some KYB Ecel-Gs for the back.

[datsunaholic]

Here's what a prior owner of one of mu '76s did:

 

However, the truck is a 4X4 so the axle is under the springs, rather than over which is normal.

 

 

 

The issue is, '79s tended to have VERY weak springs.  The added spring MIGHT work, but what would really stiffen things up is to use a spring pack from a '73-74.  I've put over 2000# in my '74 without even getting close to the bump stops.  My Mom's 73 is the same.  They came stock with a massive overload leaf.

 

That's my '74.  Only 3 leaves, but far stiffer than the 5 "thin leaf" later models.

 

The bad part is, with no load in the bed the rear springs might as well be made of solid steel plate.  The tires bounce going over speed bumps. 

[mikeanike99]

Ya my 72 620 has the massive spring I'm gonna take it out cause I don't want to be that bouncy. :P

[datsunaholic]

The massive spring isn't what makes it bouncy.  It only ever hits that with a LOT in the bed.  It takes a lof of spring deflection to hit the overload spring.  The other springs make it stiff because they're thicker as well.  Maybe the 2 of you should trade spring packs...

[Aibast]

my 79 truck has 3 leaf springs hard as hell, without load its realy stiff on bumps. With 800kg loads still has room to move around.

[datsunaholic]

my 79 truck has 3 leaf springs hard as hell, without load its realy stiff on bumps. With 800kg loads still has room to move around.

 

You don't have a US-spec one, though.  Yours is probably the 1-ton rated springs.  In the US, 78-79 trucks got softer springs to make them more comfortable, since the US only rated them as 1/2 ton.  Earlier trucks had the same/similar springs as the rest of the world's 1-ton rated trucks, even though they were only rated as 1/2 ton here.

[rjgilligan]

Just drove this thing to Pennsylvania from Olympia... this should be fun trying to find a set of springs out here for it.  Man, times like this I wish I still lived in Washington.

 

Datsunaholic, you mentioned 5 springs for the later models?? Mine has 2 and a helper on the bottom. Did some PO goober it? Looking at it again, there is some space between the spring clamps...

[datsunaholic]

None only had 2 originally.  3 + helper was the minimum (and they were stiffer than the later 4 and 5 pack springs), so yeah, I think a PO took some out.

 

This is what a PO did to my 520.  Believe it or not it works....

 

 

 

On my '78 4X4 they took out half the leaves, so it's permanently de-arched.  Makes for good articulation, but it can't carry jack, and it "drags ass" since the rear is lower than the front.  After I fix the transmission (which I've "planned" to do for over 5 years now) I intend to replace the springs with a set of '73 springs, which will probably add 4" of lift compared to the de-arched 3-leaf mess that's in there now.

[Hooligan]

I have these coil springs (helper springs) that use a U-bolt to clamp them on the axle tube and pinch on the bump stop. I removed them..... they need new U-bolts to clamp the on. I have no use for them at all

[GRpufnstuf]

Ya my 72 620 has the massive spring I'm gonna take it out cause I don't want to be that bouncy. :P

The massive spring isn't what makes it bouncy. It only ever hits that with a LOT in the bed. It takes a lof of spring deflection to hit the overload spring. The other springs make it stiff because they're thicker as well. Maybe the 2 of you should trade spring packs...

AND if you pull that overload spring you'll raise the back of your truck about a half inch!

 

^^I'm wrong about this^^

[datzenmike]

No it won't. Think about it and look at the pictures again.

[GRpufnstuf]

I did, it's like removing a 1/2" lowering block. I did it on mine.

 

 

so very wrong

[datzenmike]

As long as the upper leaves are not being supported by the overload spring then no nothing will change. I thought you meant it drops by the thickness of the removed over load spring.

[GRpufnstuf]

It doesn't change the spring rate like pulling a leaf will. But it does effectively move the axle down away from the body and so it adds the missing spring width to the ride height if the truck.

 

and I just kept going. Sorry yawls

[wayno]

It's hard to tell you what will work for you, as we don't know if you haul a lot around normally, you can try overloads like datsunaholic mentioned, but they are more or less permanent, unless you carry around a wrench to loosen and tighten as needed, there are lots of different types of these springs out there.

The one you posted a link to is permanent, if it's to stiff, you will have to take it apart to remove it, kinda a hassle.

There are also overloads that kick in when you get to a certain weight, but obviously you were not happy with the stock one.

I added two extra leafs to my 521 leaf pack, one full length, one just short of full length, they were both arched the same as my stock leafs, it made my ride much stiffer, but my truck is for work, I haul a lot of weight daily, so it is just right for me, but when I haul even more weight than normal, I use overload air bags.

I also have coil over shocks, but the overload airbags are adjustable, you can pump them up as needed, and let the air out when empty, keep in mind that I haul a lot of weight all the time, that is why I have several different types of over load type hardware on the same truck.

Here is one of the crazy things I do several times a year.

[datsunaholic]

It doesn't change the spring rate like pulling a leaf will. But it does effectively move the axle down away from the body and so it adds the missing spring width to the ride height if the truck.

 

 

 

 

I can't see how that's possible with the stock Datsun axle-over-leaf design, with the overload at the bottom of the leaf pack.  The axle is still attached to the long leaf, so removing every single leaf except the long leaf won't change the axle position at all.  You can't remove the long leaf, unless changing the suspension type entirely.   Removing the remaining leaves changes the load capacity, so THAT would "lower" it,  but the overload leaf doesn't make contact with the rest of the leaves until they go nearly straight (on the early 72-74, the springs have to nearly completely de-arched to get onto the overload)

 

Now, with an axle-under-leaf, removing a bottom overload would lower the truck by the leaf thickness.  Or, if the overload was the TOP leaf of an axle-over-leaf setup, that would "raise" it by that much.  But in both those cases, you have leaves between the axle and the long leaf.  On a stock Datsun, there's nothing except the spring perch, and that's welded to the axle tube.

 

 

What it DOES do is compress the shock absorber by that amount, because it would move the shock mounting plate by that much.

[mikeanike99]

So all it does is sit there until needed never being used?

[datsunaholic]

Depends on the type of overload.  If it's clamped to the other leaves, it's a "helper" leaf and changes the spring rate and load capacity.  If it's "loose" (with a gap) it is a true overload.  How and when it comes into play depends on the curve.  If it's flat, or even curved slightly opposite the other leaves, it only comes into play when the springs are heavily loaded, and it becomes the last think before the axle bottoms out.  Depending on the load, it could be always engaged, or only when you travel.  If the spring curves with the leaves but still makes no normal contact except at the very center, it will be more gradual.  The early 620 overloads were the flatter type, later ones the curved gradual type.

 

Most overload springs never come into play when the bed is empty, even on the bumpiest roads.  Put 500# in the bed,  they'll start functioning, like over curbs and speed bumps..  Put 2000# in the bed like I have, and they'll be fully in use.

[GRpufnstuf]

Crap, I hate being wrong. I had a couple beers and decided to be smart. You guys are right, if the overload were on top of the leaf pack what I proposed would happen.

The height doesn't change, unless you want to convert to and over axle spring and prove me right?

 

Edit: Oh dammit! Even if you went over sprung pulling the leaf would lower it. I can't even win my own jokes.

 

Ok, leave the overload in, pull the lowest leaf, flip it over and clamp it on top. That will flatten out leaf pack for some lowering and leave you most of your spring rate and overload ability?

 

So I guess I agree, get an earlier set of springs with the big overload bar still in.

 

Now I'm going to move my lowering blocks to the bottom of the stack to teach myself a lesson...

[datzenmike]

Flipping a spring should make the spring rate less as the flipped spring is pushing down on the pack by it's rated amount. Yes the spring will sag but this is not the way to go by my reasoning. You would end up with a lesser spring rate on a lowered suspension... something to be avoided absolutely!

 

 

 

Now I'm going to move my lowering blocks to the bottom of the stack to teach myself a lesson...

.

Lowering blocks go between the axle and the spring pack ... if the spring is normally mounted beneath the axle.