This is good stuff!
Leaf spring tech:
Contrary to popular belief there are right and wrong ways to setup and run leaf springs. A large benefit to links is that people who have found this forum actually take the time and pay attention to how they are setting them up because they think they have to, and they should. The same could and should also be said for leaf springs. Yes, they are old and antiquated technology, but for a weekend warrior trail rig (not hill shooter, big rock hammers-type rigs, or 450+ hp rigs) that see a fair amount of street, carrying varying loads; leaf springs are a VERY viable option. They can be setup to carry loads, go fast or anything in between. Here's the culmination of what I have learned about leaf springs over the last 13 years that I have been wheeling and building my own rigs (there's been several). Many will skip it because links rule, but for those running leafs that have issues with ride, etc. please read and then take another look at your rig and break out the tape measure. I'm not looking to change anyone's mind, just provide solutions for those that have decided to run leaves and want to get the most out of them.
Spring Selection: This is the most critical component of your leaf sprung setup. Your spring selection will determine the amount of potential travel, axle location, f/r pin offset, spring rate, and anti-wrap factors. I have tried several junkyard packs, off the shelf aftermarket packs, hybrid packs and custom packs. There is no substitute for a custom pack. Yes, you will pay for it, but the benefits will much more closely mirror the setup and tuning of a linked suspension where you pick your spring weight based on your actual weigh, locate your axle where you want it, and choose your link lengths. A custom pack will fit your rig and you can notice a difference.
1. Spring length: Spring length is a large factor in determining wheel travel. Same as links, a longer leaf will allow more usable travel; travel before the path of travel causes funny things with pinion angle. Primarily, the end of the leaf attached to the frame mount is what determines this. This end is usually the longer end of the spring. The short end of the spring can affect approach/ departure angles and plays a minimal role in overall travel. A super short spring end can cause some funny wrap characteristics.
2. Spring rate: Just as you would take the time to weigh, calculate or reference your vehicle weight before ordering coilover springs; the same should be done for leafs. For a run of the mill, common trail rig there are good options from vendors that will match popular spring lengths and rates. All Pro, Marlin and TG all offer springs with enable identical lengths and spring rates that work well for pickups and 4runners. The same can be said with rubicon express leafs for jeep models. If you've gone out of your way to shed weight, add weight or desire something different a custom spring should seriously be considered. Deaver and Alcan both build custom springs for those interested.
3. Spring arch: Aside from providing lift, leaf spring arch also affects rebound (similar to pre-load on a coilover) and up travel. The more free arch a spring has, the faster your rebound will be and there will be more potential for up travel. When considering rebound, a great analogy is that of a pinball machine. The more you compress the spring on the plunger, the harder and faster it will hit the pinball. Free arch is the natural state of a leaf spring. in this state the spring has zero potential energy. The more the spring is compressed, the more energy the spring will carry and exert when unloaded, propelling the axle down and away from the vehicle. This is beneficial in go fast scenarios. Most leaf springs and springs with free arch do not like being bent too much beyond flat (negative arch). For most, your up travel will be limited at the point that your spring goes 1-2" negative. The more arch available at ride height, the more potential up travel your suspension will have. Clearance issues will still exist with steering components etc, just as they do with a linked suspension, when trying to maximize up travel with a minimal ride height.
4. Wrap factors: manufacturers use different techniques to combat axle wrap, which is the primary draw back for a leaf spring used under extreme circumstances. Mil-wrap, double mil-wrap and special anti-wrap leaves are all popular means of limiting axle wrap. Mil-wraps also have an added benefit of being easier to trail fix after a main leaf failure. A nice progressive pack (many leaves, with each successive leaf being slightly longer/ shorter) also helps as there is a steady progression in which the leaves support each other as they are loaded.
Setup: Now that you've selected the right spring for your vehicle it's time to set them up under the rig. Improper setup can ruin the ride or function of even the best custom spring. Everything I outlined above, will come to play once it is time to setup your suspension.
1. Axle position: Just as you should when doing a link suspension, build at full bump. To do this with leaves, go ahead and disassemble the pack down to just the main leaf. Position your axle where you want it to rest at full bump.
2. Fixed hanger location: With your axle located at bump, the location of your fixed hanger will be equal to the distance from you center pin to the center of the spring eye ALONG THE ARCH OF THE SPRING. Front or rear axle, forward or rear shackle, it's all the same.
3. Shackle orientation: In the case of a front axle, there are some further considerations as to which end of the spring you want to fix. The most popular method is to fix the front end of the spring. Popular thought is that this allows the axle to move backwards when it encounters bumps, yielding a better ride. For offroad applications this presents a few problems; under droop the axle will move away from transfer case. This requires a long-travel driveline. Slip lengths of 12"+ are not uncommon for the front axle of a leaf sprung rig. Long slip drivelines can be expensive, sloppy, and heavy. Another problem occurs when climbing. Under power, the axle will drive itself out from under the vehicle, unloading the suspension. This is counter-productive to the task of trying to climb as the axle will not pull any weight until the suspension limit has been reached. This can also require even longer drivelines to keep up with increased slip requirements while the axle is under power. A third problem occurs under compression situations. Under compression the axle moves rearward and towards the vehicle/ body. This can make building a low-slung rig even more challenging as it is possible for a tire to recede several inches towards and into the body during compression. Depending on your desired tire size, it may not be practical to move the axle far enough forward before you run out of frame to attach your spring hanger to. Earlier I spoke of popular thought concerning rear shackles on a front axle. I disagree with the blanket statement that a rear shackle rides better than a forward shackle. While wheel recession should not be discounted, a forward shackle suspension pivots from a rearward fixed location; just as nearly all front link suspensions do. These have been proven to be plenty fast, when setup properly. Forward shackle suspensions do not require a long slip driveline because the axle is pivoting from a fixed end near the transfer case (same as a link suspension). During climbing, the front axle will constantly be pulling forward, on the fixed end of the spring. It is also easier to build a low slung vehicle with a forward shackle because under compression, the axle will move away from the body. Yet another consideration in this particular debate deals with geometry. I once stumbled upon a reference that suggested that the shackled spring eye, should be located higher than the fixed eye, relative to the ground. I have not been able to track it down the last f year, but consider OEM applications. Nearly all are setup this way, on both front and rear suspensions (with the exception of Toyota mini truck front axles). It is much more easy and practical to achieve this geometry with a forward shackle setup on a front suspension.
4. Shackle length: all too often shackles are looked at as a means of providing or reducing lift. Even in this thread, the OP mentioned "I'll just run shorter shackles to lower it." A shackle is designed to allow the spring to move freely from it's free arch state to it's flat length state. With this in mind, it should make sense that the shackle length should be equal to this amount of travel. To figure this out, measure the flat length of your springs from eye to eye (along the arch) then measure the straight line distance between your spring eyes, with the springs at free arch. Subtract the free arch number from the flat length number and that will tell you how long of a shackle the springs need to allow the spring to move freely. Too short of a shackle will bind the spring prematurely and "short stroke" it (not allow full travel). Too long of a shackle will try to stretch the spring and will prematurely wear the bushings.
5. Leaf sliders: lately I've been building and trying to build with leaf sliders. The concept seems simple enough and they allow the spring to work independently of a shackle. This provides a nice and consistent spring rate. With a shackle, your spring is moving through yet another arch as it compresses and extends. As your shackle angle changes during this process, so does the amount of leverage that the shackle applies to the spring. This change affects your ultimate spring rate. A leaf slider does not do this as the spring simply moves forward and backwards as it compresses and extends. Sliders also do away with the inherent "lift" of non-tension shackles, common on Toyota mini trucks. I won't get into tension shackles because honestly, I've never had them.
6. Shackle location (flop the angle): You now know how long of a shackle you need, now where to put it? I'll once again refer to popular belief, in which there is an ideal shackle angle. This is a fallacy because the shackle angle at ride will vary based on the amount of free arch that a spring has and the amount of weight that the spring is supporting. There simply is no magic angle and simply trying to follow this idea could leave you with a poor ride or a shackle that inverts. Instead I want to once again refer to the mechanics of what your leaf spring and shackle are doing. The ultimate goal of this combination is to allow the spring to move freely from it's free arch state to it's flat length state. To properly locate the shackle end, we will now focus on the flat length of the spring. I use a simple formula to determine where to place my shackle hanger. I've posted this before several times in various threads. Take the flat length of your spring (eye to eye), subtract your shackle length (eye to eye) and then add 1/2." Why a 1/2?" Well, 1/2" accounts for bushing deflection under load. It has yet to provide me with any problems and if you are decent with maintenance, you should discover a blown-out bushing before it is truly problematic. The value from the equation above represents the distance from your fixed spring hanger that your shackle hanger should be. This combination will allow your spring to move freely as it cycles.
7. Bump stops and limit straps are for springs.... Not shocks: Say what? Popular belief once again is to limit your suspension travel to preent damaging your shocks. All too often people will buy too long of a shock because they are cool and some of those people even setup bump stops and limit straps to protect their shocks. What about the leaf spring? As I said earlier, leaf springs do not like to go too far past flat, nor do they like to be extended too far past their free state. When stretched, the leaves begin to fan out and pack deformation begins. Over compressing a spring will bend it, usually near the eye, where the progressive support ends. I set my bump stops to stop up travel at 2" past flat, I do the opposite for limit straps and set them 2-3" past unloaded (with axle weight) this allows for some downward articulation. A good, cheap bump stop can be found at the pnp in the rear of '94-99 s10 blazers and jimmy's. They are a timbren style stop the will fully compress and have a convenient single mounting hole/ bolt.
8. Shocks: Just as many do with a link suspension, I recommend buying a quality rebuildable and tunable shock of your choice to maximize the performance of your suspension. I do advise buying a shock that is slightly longer than your suspension travel so that you can mount them to have 1" extra travel in each direction, from the limits of your suspension.
I hope for those that suffered through the long read that they found something useful.
