Let’s talk about leaf spring durability

If you don’t have first hand experience, please don’t post in this thread!

Hey folks. Need some advising on springs. I have a set of k37s that flattened out that I kept. Would like to get them re-arched. I just daily drive with a diamondback cover and no extra weight, and the occasional romp off-road. There’s a local place that does rearches, but how would they know how much arch to put back in em? Are they going to de-arch faster once they are redone?

Second, I occasionally, like once or twice a year I do put some weight in the bed. Hauling a load of dirt or whatever. Keith at dirty deeds told me something about some airbags that go well with k37s. Have any of you done that?

Axle wrap with k37s is a things. What have y’all done to successfully mitigate that?

Matt at MCM was saying the u748 doesn’t have near the issues with flattening or wrapping but I already have the k37s, and it’ll cost me at least a grand more, and I’m wanting best possible on road ride. I understand the u748 rides a little stiffer.

Frankly I was not going to do anything to this truck but I have had a few issues that necessitate me doing this. I’m poor, and have to do it right the first time on a budget.

Thank all of you for your help

 

@osidepunker
@831Tun
@n2deep
@dirtydeeds
@M C M

Shoot I dunno who else. Can anyone tag anyone whose knowledgeable? I really need some advising.

 

@dcsleeper408

 

you can rebuild those K37s into some U748s or custom weight if needed. which shackles do you run ?

 

Alex, @osidepunker, is guinea pigging the 3" leaf setup. This will require leaf hangar modification and shackles. Jeff, (Deaver springs) built the pack for Alex so he's already hip to possibility of the upcoming change. I think this will eventually be best option for us. Right now everything available is gonna go flat sooner than later. Just my opinion

 

Total chaos.

 

First, the U748 ride like crap. They also sag as well. I know several guys who went this route and didn't like the ride. Also one guy who had to get his re-arched becuase they flattened.

The real problem is tundra leafs are 2.25" wide. That is just not wide enough to make a reliable leaf pack that will hold the weight a tundra typically sees. Yes, you can make a thick (tall) leaf pack that will hold the weight, but it won't be reliable. When a leaf pack is narrow and thick, articulation will take the arch out of the leafs over time. The reason the oem packs holds up is because they can't really articulate that much.

I went through 5 different leaf packs (6 if you include the stock leafs) before I made the switch to 3" wide packs. Every single one of them flattened after a year or so. Some more than others. Jeff built 4 sets of LT spring under axle packs for me and after the 4th I decided something had to change. In my mind I always thought they were too narrow. So I talked with Jeff about going wider. He agreed with me that a wider pack would not have to be as thick. At first my theory was that a wider pack that was thinner (not as tall) would hold up better because each leaf would have to do less work. I am now convinced that the real reason is because a wider thinner leaf can twist more than a narrow thick leaf without losing arch. Anyway, bottom line is Iv'e been running 3" leafs for over a year and they are holding up. I have lost exaclty zero ride height.

Because I'm SUA I really want thinner leaf packs so they don't hang as low. That the real reason I went down this path. I wanted thinner packs that wouldn't hang as low and I had a secret hope that they would be more reliable. The new packs are 3/4" thinner than my old pack, but I gained 4" of lift. It was a drastic change. No matter how Jeff built the 2.25" wide packs, they just would never give me the ride height I wanted. My rear always sagged.

I would actually do 4" wide packs; they would be super thin. But there are challenges with mounting and clearance on the axle. Plus, 3" leaf stock is what Ford uses so the material is plentiful and available.

3" packs are the answer for every tundra out there. Even spring over axle mid travel trucks. But there is a cost involved with the upgrade. You have to install a new front leaf hanger. Redoing the spring perch and rear shackle is actually pretty easy. DMZ charged a lot to do the conversion on my truck but the front hanger turned out super awesome. @papasmurf is working on a cheaper alternative.

If you don't want to spend a bunch of money, then just do K37s with air bag cradles. Lots of guys run that setup. If your K37s flatten, just have Jeff re-arch them. Its not that expensive. I'll keep you guys posted, but I run my truck HARD and I have 4000 lbs on my rear axle at all times and its been holding up going on two years of wheeling...

 

Will eventually be replacing rear springs too
Too many questions !!!

 

Alrighty. There’s local places in Houston that will re arch the springs. What spec would I give them to re arch the k37 to?

I’ve had major problems the last few days with the rear suspension. I’m about to limp home from Michigan to Texas and then the entire rear suspension is out ASAP. The local guy can turn around the springs real quick for me, otherwise I’d just send them back off to Deaver.

Thank you

 

The shop doing the re-arch should know the "specs". If they dont, then they're not a good shop.

When deaver does a re-arch, you just drive your truck in, sit around for a couple hours, then drive off. I wouldn't bother taking them off myself

 

I don't know if it's just great intuition or what, but your idea about a wider pack with thinner layers is exactly right.

From an engineering perspective there are two types of bending: "elastic bending" and "plastic bending"

If a part experiences elastic bending:
1. It returns to it's original shape after the load is removed (no permanent deformation)
2. Its material properties (strength) remain the same as before.

If a part experiences plastic bending:
1. It does not return to it's original shape after the load is removed (permanent deformation)
2. Its material strength is reduced.

All solid materials experience elastic bending before plastic bending. The material type and shape will determine how much they can bend elastically before the bending becomes plastic. For a leaf spring "plastic bending" = "damage". The only way to fix the spring once it happens is to re-bend the curve and re-temper the metal.

If two items are made of the same material and one has a thinner cross-section it will be able to bend farther than the other without permanently deforming. To increase flex limits without accelerating fatigue you need thinner material or fewer layers.

To increase load carrying capacity with thinner leaves you either need to stack more of them on top of each other or you have to make them wider. Stacking on more leaves does increase the load carrying capacity, but it also reduces the how far you can flex it without damaging the spring. Alternatively, widening the leaf pack increase your load carrying capacity and also doesn't change how far you can flex it without damaging your springs.

For flexibility *and* load carrying capacity *and* long-term durability wider leaf packs are better than taller leaf packs.

 

haha I'm a systems and hardware engineer, basically a jack of all trades. You're absolutely right about the material fatigue. I wrote my explanation without trying to sound like an engineer though LOL

 

@papasmurf is really close to having the new hangars ready, if we can get him out from under his bow tie. There's an existing hole in the frame where a bolt will be used to locate the new hangar, don't remember if the rest is weld on or what. For now I'm going with the I96 SUA pack but plan to eventually make the change to 3" leafs.

 

Weld or bolt, dealers choice

 

Technically the hangers will index with 4-6 bolts, but I will be full welding mine on. I don't think 6 grade 8 bolts is enough for a LT truck like ours mashing, but for a MT guy it might work ok, but once you index with the bolts, you can always then drive to a place to burn it in with a welder.. shouldn't take more than 30-60 minutes to do.

 

don't worry ill be done with the "like a rock" project soon... ill put up a thread about it

 

Is the route that you went cheaper than just linking the rear end, like on a trophy truck? Seems that both are both probably fairly expensive.

 

Shit, you know that’s way more expensive! But super awesome and I totally freaking want that!

 

In my experience, I wouldn't say they ride like crap.. Maybe not as good as K37's, but still a lot better than the stock setup. I will say that Oside is dead-on about the sag though.

 

I was talking with Tim at DMZ fab today about links. Our gas tanks are in the way of doing a proper 4 link rear. Once you move the tank and go to a fuel cell you're not really street legal, none of these suspension mods are truly street legal though. We also spoke about cantilever rears and how at the end of the shock stroke on a cantilever you're losing leverage so tuning becomes nearly impossible. So, costs aside a bed cage and 3" leafs are probably the best we can do for our trucks while remaining semi street legal. Probably the cheapest option too.

 

that looks like Roy's truck

 

Don’t forget this option. When @papasmurf gets the 3” spring kit ready, going to switch and be done with it.

 

Are you referring to the Spring-under option?

 

all hail the KING !

 

Yes, mine is SUA. Not sure if it hasn’t been brought up, but the @papasmurf 3” spring kit should work for spring over as well. Lots of options with the wider spring.

 

This seems like a stupid question, but couldn’t a coilover be mounted in the rear in the same orientation as the bumpstop to act as a supplemental spring? If the leaves keep giving out, what about using them more for aligning and cycling the axle, then a coil spring, maybe even a dual rate setup helps support weight of the truck

 

Something like that might be coming on the 2021.

 

I'm an un-reformed mechanical engineer. That post could have been 5 times longer, but everyone would loose interest so I wrestled myself down to what I posted.

 

I wonder if they just slightly moved his gas tank then, because that looks like a stock gas tank