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Go Fast Leaf Spring Tech

'84 Bronco II

El Chingón
Joined
May 19, 2020
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I know, leaf springs are for poors :flipoff2:


Now that I've got that out of the way, how about some discussion on what makes for a good "go-fast" leaf spring suspension? The discussion doesn't need to pertain necessarily to my unique situation, but I need to figure out what I am going to do for my rig.


I am building an early Bronco for the Ultra4 4600 stock class with the primary intention of racing King of the Hammers and am required to keep leaf springs in the rear. I am planning on running the longest shocks that are allowed; 14" of travel set up for a roughly even 7" up and down. I can do whatever I want with the leaf setup, but the axle location can only move up to 3" (I am planning on going 2" back with it), and the leaf spring must be capable of supporting the weight and locating the axle on their own (no 4-links with double shackle leaves, transverse setups, or anything crazy :flipoff2:).


Shackle and Spring Mounting Configuration

The Bronco uses a factory tension shackle setup which I want to stay with since it helps keep arch in the springs with a spring over setup at maximum compression, and is more "stable" than a compression setup. I know a lot of desert guys go spring under to combat axle wrap and help keep arch in the spring at full bump, but I think I will be fine with the tension shackle arrangement and a traction bar unless someone can convince me otherwise. Obviously clearance is at a premium racing the Hammers on 35" tires, so I am pretty opposed to going spring under.


Spring Length and Center Pin Offset

The factory Bronco springs are 48" long with a centered pin, and I don't think 48" long springs are going to last very long with 14" of travel. I want to run longer springs since with additional length the springs will see less stress for a given displacement (better fatigue life). Longer springs will be more prone to axle hop, but that's where the traction bar comes in. It looks like I can move the shackle hanger ~7" back on the frame, which along with moving the axle back ~2" would give me ~29" from the centering pin to the rear eye. I think I am probably going to have to get custom springs made because I am not aware of any good off-the-shelf options that are fairly long with 29" on the long side between the centering pin and the spring eye.

With the forward spring mount in the stock location, that would make for 53" long leaves which still seems on the short side, but I can move that mount as well and I don't have any major limitations on where I can put it. If I move the front mount forward enough to have a centered pin, that would give me 58" long leaves. I've heard that you shouldn't run the long end of a leaf forward because it will give you really bad axle wrap, but does it matter if you have a traction bar? Are there any other undesirable side effects that would arise from having the centering pin offset to the rear (long side forward)? That would allow me to run even longer springs, which may be unnecessary if shorter spring would suffice, but perhaps there is an off-the-shelf option I could run backwards if it would be non-issue. Is there a rule of thumb for spring length relative to travel for reasonable durability?


Leaf Spring and Shackle Geometry

I noticed people tend to use fairly aggressive shackle angles (~45º±) on crawlers with fairly flat springs to get a lot of droop, but what kind of shackle angles are ideal for going fast with a good amount of up-travel? How about for tension shackles? It seems in a tension arrangement, the shackle angle is a lot less critical than a compression setup since inversion isn't really an issue. How about shackle length? I know more travel requires longer shackles, but what is the relation between travel and shackle length? of course spring arch will have a large affect on this relation since more heavily arched springs will grow more under compression. Long shackles will create issues in a compression configuration (more lateral axle movement); although this seems like less of a problem in a tension arrangement, but still an issue.

I've noticed most factory setups place the forward spring eye significantly lower than the rear eye; even in compression shackle arrangements. What effect does this have on suspension behavior? Is this something I might want to change if I move my forward spring mount?
RCVD2_zpsocdfwqeg.jpg



Leaf Spring Construction

It seems leaf packs using lots of thinner leaves rather than fewer thicker leaves are preferred for performance/custom applications. The claim is that they ride smoother/better, but from what I've read at the expense of more weight for a given load capacity. Is that true generally speaking? If so, is the weight difference significant or even worth caring about? Regardless, it seems there is a practical limit to the number of leaves you would want in a given pack.

Military wraps are obviously a good idea as a safety in the event of a main spring failure, but I've noticed many performance springs only have a military wrap on the forward spring eye like these Deaver Ranger Race packs:
Q80-or-L27-2-e1529350271406.jpg


Is there a reason not to wrap both ends? Does the shackle end just see a lot less stress? :confused:

It seems like wider leaves would increase the roll stiffness and thinner leaves would promote roll. The original Bronco springs are 2.25" wide, is there an argument to go wider or narrower? I know 2.5" seems pretty common, and 3" seems to be used almost exclusively in heavier trucks.

Reverse eyes will allow for more arch at a given compression height, but are they weaker? It appears most Deaver packs have a normal eye forward and a mid eye at the shackle end. Any pros/cons for different eye configurations other than the amount of arch they create for a given spring height? How much arch should I be shooting for, and can you have too much? I know for longevity you don't want your spring arch inverting during travel, and ideally you should still have some arch even at maximum compression.





I've asked a lot of different questions and touched on several topics, so I don't expect someone to answer everything at once, but hopefully it got the ball rolling and will lead to some interesting discussion. My goal for this thread is to be helpful for anyone designing a leaf sprung suspension, although I am primarily focused on rear suspension for the purposes of this thread. I am hoping if nothing else to become a bit more educated on what I might want/need before calling up spring companies and figure out what I need to do for my build :homer:
 
Military wraps are obviously a good idea as a safety in the event of a main spring failure, but I've noticed many performance springs only have a military wrap on the forward spring eye like these Deaver Ranger Race packs:

Is there a reason not to wrap both ends? Does the shackle end just see a lot less stress? :confused:

I'm not a leaf spring designer but I would assume you see them in the front because the case when they would fail would be forward travel at speed. Having the front wrapped keeps the front from stabbing into the ground and Pogoing the vehicle or rolling the axle under the vehicle. The rear you dont care as much about because if it fails it will just "drag" it along.
 
Ignore the specific construction of the leaves for now. Because you are in a time crunch that is a job you would be best left to Deaver via Mastercard. Spend your limited time thinking about geometry.

You can build leaf packs with all sorts of spring rate curves. They're far more tune-able than coilovers in this regard but without highly specialized simulation software you are limited to trial and error. It's very easy to build a one trick pony such as a low spring rate for where the truck rides unloaded and then an ungodly spring rate when you've got shit in the bed. Building a spring pack that has multiple points where the spring rate curve change exactly how much you want exactly where you want is going to be very tough.

You're correct that thinner leaves are worth the weight tradeoff. You're also spot on about thinner leafs offering substantially less roll resistance. I strongly suspect that there are longevity factors at play too but don't know enough.

They don't wrap the shackle end because the front does the lion's share of controlling the vehicle, particularly resisting torque. I've never heard of reverse eyes being weaker.

As a leaf spring compresses the axle moves in an arc relative to the front hanger (chassis). Depending on the location of your mount points and the shape change of the spring (big arch to small arch, small to flat, flat to negative, etc) over the travel you can change the shape of that arc and the rotation of that arc. Figure out what arc of motion you want for the axle centerline. Then build to achieve that. Axle movement that shoves the spring into a rock to help you climb will beat you to death in the desert.

I wouldn't focus too much on amount of arch. Just don't get stupid mud truck with it. Generally people shoot for a flatter spring because that's easier to tune the rest of the geometry around. With flat springs that don't get very var from flat as the suspension cycles your driveshaft and shackle problems become smaller. Keep in mind that arch has a large effect on where the axle moves relative to the chassis under compression. That said, more arch is more potential to move the axle back and the shackle back and depending on shackle length that could push your (tension) shackle past vertical and change your spring rate a lot. That's not necessarily a bad thing if you're trying to get the rear to hook as you drag it over an obstacle.

You need to spend some time reading about how the plane of the leaf spring mount affects handling as well as the angle of the springs relative to the chassis. You can inboard/outboard the front/rear mounts relative to each other to affect handling (i.e. not parallel like in the above illustration). There is all sorts of dirt track stuff written about this but be warned, most of it makes generalizations that assume you are running 60s car geometry.

Tension shackles are indeed more flexible in that you need to be a bigger moron to make them bind up like a compression shackle. Just always be cognizant of the arc in which the shackle is causing the rear of the spring eye move (and by extension, the axle).

Longer springs make a lot of geometry easier because there's less arch change and less length change per travel and that greatly simplifies fine tuning the other nine million variables you care about.

But take that all with a grain of salt because while I've put together dozens of leaf packs and gotten decently good at it, I've never fucked around with something that has as much travel as your bronco nor have I strayed very far from OEM spring hanger geometry.
 
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Do the rules explicitly state the leafs have to be used the same way the stock ones are? I’m sure I could come up with some crazy leaf spring half way down a trailing area deal to get more wheel Travel type setup.

Edit: evidently you just need to buy some mile long leafs lol

https://giantmotorsports.com/index.p...ng-travel-kit/

Someone fucking around with hangers would be money ahead to buy long travel springs for an '08+ Superduty. They run 66" leafs from the factory and have a stupidly massive bushing that lends itself better to our kind of abuse.

All the R&D of figuring out exactly where the spring hangers need to go and whatnot for a bolt on Bronco/F-series kit goes out the window when you try and bolt it to something else. There's no reason to pay for R&D you can't use.
 
Not sure how much tech i can bring but my last rig did have a set up similar to what you are talking about. Now it was a big ass trail truck but i got the go fast bug and had some go fast parts laying around. My set up was used 6" lift Superduty Deaver rear springs that i pulled some out of to make 4" lift, now i did run them backwards as the superdutys have a offset pin. Went with tension shackle set up with super ghetto shackles, 2 stock ford shackles welded together to get the length :homer: Had the shackles set up so that i was pretty much 50/50 on travel and used all 14" of my shock. Shocks where 14" bypasses and mounted off my ubolt plates as well.

i really liked the set up as was very smooth and had almost zero axle wrap even with the big block and sticky tires or cut 44s . with the leaves and shocks out boarded it was every stable and i never felt like it needed a sway bar

picture of my set up to give you an idea

Z7DucHNnmG8tODi3R-ztKrDWI5cDit5EPcjrmbsHdMouO-OaEIKN0F7AEtxREdcTadZgeGVGciqcnvLjEHD3PqYVQlfyh5FbXGwoRIjG7jQ5rgOH62wQ_k6BDWkiLSI0xIHEp30IoQ=w2400


wZN_EghGW_65zuoiMmiVGCbwVcVHB57IMlAv217LgQoEARbDyJcfwhJGwUyc04Td1XuU9gUowL98oZI60WwjbMuv-8glCm1bXsSGcZb6OzJ96FQ80r7b9IgQIg6n5-4g3nz-36fA2w=w2400


and thats 6500 pounds and it was smooth as a cloud of titties :smokin:

uecKqFzz2JXmlxoZ8MKcz-06aYSFXGJmbZWljEkA83kSnPm5jfzZk0VCaV4_5_2ajHouRJUpRkCJy2hqlzdaZ4VymODj7jBFBTuKJ29asAAgShAcYZEQ-hcxyFKNkb3um-jY23Z4Zg=w2400
 
Not sure how much tech i can bring but my last rig did have a set up similar to what you are talking about....

I wasn't gonna say it since I don't think my experience on street trucks is representative but man a loooong tension shackle that never goes past 90 worked well for me too.
 
Jes Regarding the overall leaf angle and geometry, I don’t know much maybe Jes remembers better or can talk to Crash but our friend Andy has an XJ. He had had the rear leafs in the factory frame mount with a dropped shackle mount, as XJ guys do. He later removed the dropped shackle mount and dropped the front of the leaf spring, angling the front of the leaf pack down by several inches and I think reported much improved handling at speed and probably minimal change to crawling.

I think. Probably. Maybe.

edit: probably would have had decent shocks (7100s?) with no valving changes before, after, or ever, and probably would have had no changes to the leaf packs themselves.

and this is why anecdotal evidence is shit.
 
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Everything arse_sidewards said, 100% agree. That shit is way more into it than I would ever get but some solid points.


I dabbled for a while in leaf spring tuning(but more for rock crawling) and I always went with thicker and fewer leafs because I didn't want to spend the money on Deavers or similar. Because I was cheap, my rear end(XJ chassis) didn't flex very well but it had amble load carrying capacity, minimal axle wrap, and no bouncing when on steep climbs or waterfalls. I was using a stock front mount with a lowered rear shackle mount. I only broke one main leaf in about a decade and 100,000 miles of abuse, the thing worked well for what it was.
Contrast that to what Phil was lamenting. Our buddy Andy, with an XJ setup very similar to mine, had Deavers and though they worked way better(smoother) in fast stuff and offered better flex than mine, they fell short in other areas. Longevity wasn't there, he broke multiple leafs in less than 40,000 miles, had bad axle wrap, and hopping on climbs. He also would sag them out in short order as he used his rig for hunting so it was loaded down fairly often. It probably was geometry related but the laminated steel things are voodoo to him and myself apparently.
I went to coilovers long ago and Andy is doing the same soon.
Leaf springs can work, I've yet to ride in a rig with long travel leafs that work well but I'm sure they're out there. Best leaf sprung rig I've ridden in was my friend Porch Puppy in Ridgecrest. He had a mildly built 2001 Tacoma that he put together for desert stuff. He custom valved some Fox shocks for the rear and it was butter! I was amazed that a pickup could handle the whoops so well.
Sorry for my worthless rambling but it's been a long week. :flipoff2:
 
Someone fucking around with hangers would be money ahead to buy long travel springs for an '08+ Superduty. They run 66" leafs from the factory and have a stupidly massive bushing that lends itself better to our kind of abuse.


this all day long, 08+ SD leafs are my new go to rear leafs replacing the 63" chevy leafs i used to use
 
I know, leaf springs are for poors :flipoff2:
.....
How much arch should I be shooting for, and can you have too much? I know for longevity you don't want your spring arch inverting during travel, and ideally you should still have some arch even at maximum compression.

Dredging up this oldie.
'84 Bronco II, are you done with Bronco yet? Distracted with a buggy build?

I'm also wanting to improve ride at higher speeds in my pig. Has cheby 2500 4 leaf 63s with no overload. 3" block. Floating traction bar. Comp style shackle. Tuned Fox 2.0s. Heavy Sterling 10.25, 40s. Springs have some arch at ride, about 4", so about flat at bump. Considering going to a lift spring and no/minimal blocks.

I see Deavers are now over $1000. I understand more leaves, but WHY is more arch 'better'?
 
Flat springs also go negative when you are pushing for higher travel numbers.

Spring under always works better. It also gives a better motion path to the axle and has less DS plunge. Single point traction bar off the top of the pumpkin and your set.
 
I'm around a few leaf sprung vintage style desert racers. One is Toyota 4 runner/truck with the race series Deaver springs. They are super nice but they wear out in about a year, ~ 5 races. Deaver says yeah so that's normal. So not sustainable for most to shell out that kind of money once a year. And yes broken leaves and wrap are an issue as well.

The best luck has been a buddies blazer (Stock mod)which has a junkyard conglomeration of springs and it rides very nice, obviously his class is limited by travel.

The SD springs sound like the ticket, not sure I'd run out spring under, nice skids under the pack and pick your lines.
 
I'm around a few leaf sprung vintage style desert racers. One is Toyota 4 runner/truck with the race series Deaver springs. They are super nice but they wear out in about a year, ~ 5 races. Deaver says yeah so that's normal. So not sustainable for most to shell out that kind of money once a year. And yes broken leaves and wrap are an issue as well.

if your buddy is racing in the dezert and is somewhat fast, his setup is seeing far more abuse than most.

fun fact, coil springs break and are a consumable as well. main difference is people just crank up the preload to compensate for the spring fatigue.
 
I don't know about fast but yeah they get raced. And while not quite a straight across comparison another racer is the same class has a F150 with Deaver's but they are just the regular lift spring series and they have held up great.
 
Dredging up this oldie.
'84 Bronco II, are you done with Bronco yet? Distracted with a buggy build?

I'm also wanting to improve ride at higher speeds in my pig. Has cheby 2500 4 leaf 63s with no overload. 3" block. Floating traction bar. Comp style shackle. Tuned Fox 2.0s. Heavy Sterling 10.25, 40s. Springs have some arch at ride, about 4", so about flat at bump. Considering going to a lift spring and no/minimal blocks.

I see Deavers are now over $1000. I understand more leaves, but WHY is more arch 'better'?

I completely forgot I made this thread :homer:

The Bronco is still waiting on critical parts that I ordered last year :shaking:

As you noticed, I'm more excited about the buggy build right now so that is what I have been working on lately. I am hoping to get it to a roller state, then switch back over to the race Bronco. I also got side tracked doing a bunch of sheet metal work and swapping drivetrains around on my '75 Bronco that is taking up my lift bay at the moment.

I don't remember what information I posted about the leaf springs in my Bronco thread, but I'll post up the details here too when I have some time to get some pictures and look up the specs I ended up with. I ended up ordering some custom Alcan springs since there weren't any off-the shelf springs I wanted to go with, and they were great to work with. I never could get ahold of the guys at Deaver, so screw them. National was horrible to try to deal with and gave me a 26 month lead time when I talked to them :shaking: I forgot to try Atlas, so no idea how they would have been.

I can't say how good they actually are since they are still sitting on my garage floor, but they look nice.
 
How about a recommendation for antiwrap bar? I saw something further up the thread about a single link overtop of the diff, which is an intriguing thought. Same theory as the two parallel single lower links, but without more shit to get hung up on. Anyone try this out?
 
How about a recommendation for antiwrap bar? I saw something further up the thread about a single link overtop of the diff, which is an intriguing thought. Same theory as the two parallel single lower links, but without more shit to get hung up on. Anyone try this out?
I did this on my 77 bronco and it worked really well. Rod end on diff end and poly bushing on chassis end. In theory this will bind but worked well in street/trail/rocks/sand. This is 20 years ago, learned a few things since then. 400hp 347 stroker, 4.56 gears turning 37s.
full.jpg


and those 11 leaf pack springs were a HUGE improvement over the worn out stock leafs + blocks
 
think of it as preload.

you want the spring to want to return to its natural state, this helps with packing. flat springs just want to stay flat, so when you get into the chop and other things they dont want to get back to the ride height state.
Thanks this is what I was looking for.

Can I barrow some money for new set of decent springs?
:smokin:
 
Turns out I posted pretty much all the info in my thread, so I'll just cross post it here:

The leaf packs from Alcan are 58" with a centered pin. They are basically 5" longer front and rear than a stock Bronco pack and arched for 4" of lift (obviously this depends on how I set up my perches). They are also 2.5" wide compared to 2.25" for factory Bronco packs, and are an 8 leaf design with a half leaf on top to help control axle wrap. They have Alcan's "orbit eyes" at the back which should help the bushings and springs themselves live longer while providing more articulation.
IMG_5969.jpg

These springs are built for 900Lbs. capacity each based on the weight estimates I gave Alcan. Alcan sold me on their 6" "custom" shackles, but I am unimpressed with what they sent considering what they charged me. I was expecting something nicer than bent 1/4" plate for $200. I'll probably modify them and tie them together.

The other springs I was considering as a COTS option were the Deaver G50 Ranger Race packs, but with the 31" behind the center pin, I would have had to keep the rear axle in the stock position, or stick the low-hanging shackle mounts out past the end of the frame. Wayne Todd, "68ford" over on Classic Broncos, runs them in his bad ass Bronco with great success paired with 3.0" 16"(?) bypasses. You can see how far back his shackles ended up with the rear axle within 1" or so of the stock location:

Screen Shot 2022-07-29 at 4.38.30 PM.png

Screen Shot 2022-07-29 at 4.38.54 PM.png


016-early-bronco-feature.jpg?fit=around%7C770:481.jpg
 
Any updates? How’d the Alcan’s with Orbit eyes hold up?

Great so far just sitting in the shop :homer:

Alcan sold me on them because they claimed springs with the Orbit Eyes had way better bushing life in racing applications which is something I was worried about. Obviously the trade off is that you lose some of the natural sway bar effect of the leaves.

Someday when dinosaurs once again roam the earth, we'll find out when (if) he finishes the build :flipoff2:

That cuts me deep man :flipoff2:

Maybe I can be the new Sceep :laughing:

Had no idea the orbit eye deal was still an option. Interested in feed back also.

What did they run?

I am not sure how much the orbit eye option itself runs, but the 100% custom packs were ~$1,200 with the orbit eyes from Alcan. National Spring gave me a similar estimate but without the Orbit Eyes obviously, so I don't think they are a huge expense if you are already going down the rabbit hole of custom springs anyway.
 
Great so far just sitting in the shop :homer:

Alcan sold me on them because they claimed springs with the Orbit Eyes had way better bushing life in racing applications which is something I was worried about. Obviously the trade off is that you lose some of the natural sway bar effect of the leaves.



That cuts me deep man :flipoff2:

Maybe I can be the new Sceep :laughing:



I am not sure how much the orbit eye option itself runs, but the 100% custom packs were ~$1,200 with the orbit eyes from Alcan. National Spring gave me a similar estimate but without the Orbit Eyes obviously, so I don't think they are a huge expense if you are already going down the rabbit hole of custom springs anyway.

$1200 with the $200 flat plate shackles? :flipoff2:

I think a pair of all pro leafs for a Toyota was like $650 about 8 years ago. Probably at least $800 now, so $1200 for something totally custom isn't bad imo.
 
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