Leaf spring tech.

[Tiha]

So spec'ing new leaf springs.

What happens when they are too light for the load?

When they are too heavy? (I would imagine harsh stiff ride, because no flex)

So why do lift springs seems to bounce more?

I would assume more bounce because they cannot carry the same load?

So flex is good because it absorbs road shock, but bad because it deflects the truck and body upward? Is that what is happening?

Lighter weight multi leaf vs less leaves?

the more I think about it my head becomes like a pretzel. Gotta pretzel in my head.

My 1995 F350 4x4 diesel, 4" lift, RSK on factory springs. Had no ride improvement with RSK, which now we understand is because the spring is so flat.

Running over the same stretch of concrete in my 1995 feels like it will bounce you to the moon. My son's excursion with brand new factory springs seems to run over it pretty decent. Very similar to 2014 super duty.
I understand the OBS will be choppy but it shouldn't feel like a slingshot. It used to ride pretty decent but over the years it just keeps getting worse.
So I am removing the RSk returning it to factory. Want to buy the right springs so maybe it will ride like the day I bought it.

No I am not swapping axles or SD springs up front. Just trying to get the best product for factory specs.

So how to pick a leaf spring with enough flex but not too much flex?

 

[arse_sidewards]

There's a million variables involved in leaf springs and they all affect each other.

Part of why people love coils so much is they're stupid simple.

Lift springs tend to rebound hard because the overwhelming majority of them are stupid stiff and even if they're not the highly progressive nature of leaf springs (particularly the shorter ones that tend to be found in the front of vehicles) means that at the bottom of however much a given bump has compressed it has a hell of a lot of force to push the body back up.

Most shocks really don't play nice with the progressive nature of leaf springs. Shocks progressive with regard to speed whereas springs are progressive with regard to distance. Until you start talking bypass shocks most shocks do not have valving that compensates for where they piston is in the travel range (except potentially at the extreme ends) so a shock that lets you have a smooth ride over a little bump necessarily lets the spring kick you real hard on a bump that compresses the spring more or lets you bounce all over the place when the vehicle is loaded down. And a shock strong enough to prevent the spring from pushing the vehicle around when empty or keep things from bouncing when loaded is going to give you a really rough ride over the little stuff.

A pack of many small thin leaves is easier to tune and can flex better but that tends to come at a cost of some durability (particularly the main leaf)

Without an OEM R&D department guess and check is going to be your best approach.

If I were you what I would do is get a pair of leafs from a '11+ superduty (might not be 11 but whatever year they went to the 66" leafs).

Take the main leaf and the tapered overload leaf and one leaf that looks about right to go between the two and make a pack out of that.

If it's too soft initially add another leaf above the tapered leaf and below the main. If it's too soft when loaded add another leaf below the tapered leaf (or grab another pair of tapered leafs from the junkyard and throw those down there).

I've had a lot of success building leaf packs this way. I'm not sure why the OEMs don't use tapered leafs in the main pack (I suspect longevity issues but I've done some stupid stuff and haven't cracked any)

For the front the best bang for your buck is to bust out the welder and convert it to radius arms. Other than the brackets on the axle which you'll need to fab it can be done with all bolt on Ford parts.

If you just want it to be easy and don't care about bang for your buck call up a premium spring builder (e.g. Deaver), ask for recommendations and then give them your credit card number.

 

[Tiha]

That is great info, thank you.

I had thought about doing a coil spring or 4 link on my front axle. It looks like it would be stupid easy. But then I want to put in a 6R140 trans too.
It just never ends.
I gotta stop, just enjoy driving it and leave it at that. Can't do that when it is always torn apart getting upgrades.

So my rear springs are 5 leaf. From what I read that is 2975 pounds.
If I get into a lot of towing again I figured I would add bags later.

So wondering is I should be looking at 2450, or 2810 4 leaf rear springs.

front springs are 2 leaf 2,200 pound. Not a lot of options there.

But those weights give me a target on custom building springs.

I have some decent spring builders here locally but none of guys seem very knowledgeable. I pretty much need to walk in there know exactly what I want to start with.

Shocks are another great point you brought up. You just can't get a shock to work at both ends of the spectrum. Exactly right. To me shocks seem more like they are there to cover up a problem rather than fix it, but then I never spent the big money on them either.

 

[fordpickupman]

Good shocks are worth the money.
I’m running 2019 F250 leaves on the rear of my ‘96 F350 with a shackle flip. I added a leaf from the F350 pack to the bottom and a big overload pack on top. It rides way better and hauls the camper and gooseneck just fine.
I haven’t had a chance to RSK the front yet. I’m anxious to get it done so that the front ride will match the rear.

 

[u2slow]

I went to rough country 4" leafs on my 95 f350 (crew/psd) and wished I'd done the RSK with SD leafs instead. Better ride from tapered leafs IMO.

Similar to fordpickupman I swapped in longer rear leafs on my dodge. Huge ride improvement.

 

[reptillikus]

I had my truck (96 F350) set up several different ways. 6" Skyjackers (that sucked), then stock F350 leafs with Sky 3.5" SR, then X-codes with PMF 2.25" SR. The X-codes ride the best of the 3, despite having the highest spring rate. I know i could switch to V codes for the lower rate (and lift) and it should ride smoother, i just havent gotten around to it. The overall length of the pack, # of leafs, width, thickness, how long each individual leaf is, the end cut on them, anti-friction pads, mount location, shackle angle/length, there is a ton of little things that affect how a leaf spring works.

arse_sidewards touched on some good stuff, but i wanted to mention shackle angle. If you have a positive arch spring, you want the shackle behind it. If its flat or slightly negative, you want the shackle in front. If its a positive arch, when you hit a bump and the spring flattens, it gets longer. The axle will move towards the shackle. So if the shackle is in the front, the tire pushes forward into the bump. This makes it ride harder. Move the shackle to the back of the spring, and when you hit that same bump the axle moves backwards slightly, which lessens the hit, and makes it ride smoother.

Remember these trucks were designed to have TTB in all models- F150 thru F350. The D60 was an add-on a couple years later. Why mention this? Because the F250, D50 TTB, has flat/negative arch springs, and a front shackle. When you hit a bump the spring goes into a negative arch, and the axle/beam/tire moves backwards with the bump which lessens the hit and makes it ride smoother. But then Ford stuffed a D60 & positive arch springs under there a couple years later w/o redesigning anything, and suddenly it rode rough. Well thats why it rode so much rougher.


Shackle angle has an effect as well, altho not as much as location. Make sure its angled slightly forward (so the fixed end of the shackle should be slightly forward of the bottom). Doesnt have to be 45º, but even 5-10º will help. Also, the longer you make the shackle the more leverage it has on the spring, so stay away from those 8" lift shackles at Autozone! Please note this is only true if the shackle is in compression, like it would be from the factory in the front. Switching the shackle to tension (like the OEM setup in the rear) changes all this.

Vertical height of the two spring eyes also affects the suspension, however in front setups typically they are both pretty much level so its irrelevant.

 

[fordpickupman]

Shackle angle is huge. For some reason 15° is stuck in my head from when I built my highboy with SD fronts and 64” Chevy rears with a shackle flip. It rides so nice I’m trying to mimic the setup on my bride’s OBS to match.