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Leaf spring mount distances and shackle lengths...

RSWORDS

RSWORDS

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Im.pretty sure it was @Wilsonthat had the formula where you took arc length, flat length, and did theath for shackle length and mounting distance.

Damn if I can find it though. I see the "hard core leaf spring" thread but don't see the equation
 
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 (fawk 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. T

ake 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.

Wilson
 
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.
 
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.
 
Setting up axle location with the spring at full bump will render the axle forward of the wheel well at ride height. Been there and it sucks redrilling the axle perch to get back that inch or so that was lost. As far as front setups go. If you fix the rear, then the front shackle should be higher off the ground than the rear mount. That way it helps eliminate the axle moving forward under bump. When you hit an obstacle and the wheel moves forward, it makes the hit that much harder, upsetting the entire truck. Also, inverting the shackle and/or bending the leaf pack is a lot more commons. Fixing the front of the pack allows the suspension to act like a trailing arm suspension. Which has been proven to be the best design for ride quality. When it drops out the wheel base increases for more stability. And when you break over, the axle can actually walk ahead of its normal location, helping pull the truck over. That same dynamic can have a lifting affect where it would be a lowering affect with a fixed rear. But ive never noticed it to be a problem. Lastly, the fixed point is where the axle pulls or pushes the chassis over an obstacle. The sooner that points gets over or past the obstacle, the better. As for shackle angle, more isnt better. You need just enough to prevent inversion. I might find myself going to a shorter leaf up front just to stand the shackle up more. To prevent the lifting/ unloading characteristic. It will also limit travel though. Anyways, that's my long winded take on things. Lets hear other debate. I'm sure I haven't thought of everything.
 
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Provience said:
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.
Click to expand...
Exactly what I was looking for. That equation works every time
 
Recognize that said 'formula' establishes a minimum only. You may or may not have the freedom to move the shackle attachment on the frame. Depending on the setup, you can usually overshoot to satisfy other constraints. A couple examples:

- on flat (stock type) front spring you can lengthen the (rear) shackle for lift and improve the caster. No real downside, providing ujoints don't bind.

- on a stiffer curved spring, angulate the shackle (and lengthen as needed) for improved ride.
 
Thanks for posted this thread, I was going to set my shackle angle stupid shallow so that I had a lot of droop without the chance of inverting the shackle. Now I have a reference to work off of, so thanks RSWORDS & Wilson

I am after ride quality with some RE1430 springs. Currently not installed but "the formula" should get me close!
 
We just had another thread about shackle angle recently, I posted in that...

The "formula" may work, but it may also fail miserably. Leaf springs are a huge "it depends" situation because there are so many factors that can vary truck-to-truck.

Also, that formula would result in shackles that approach horizontal at ride height the flatter the springs are at ride height. The formula only provides a bare minimum mounting distance to avoid shackle inversion at full compression.
 
Found the other thread...

irate4x4.com

Shackle length v angle

Does a shorter shackle length cause a noticeable difference in angle over long lift shackles? I can add more details for my story but the short version is I have currently have long shackles with a shitty angle and looking at options
irate4x4.com irate4x4.com
 
Bumping this to the top for insight!

Potato pics but what you are looking at is the following: 47” spring arch minus 4” shackle length… plus 0.50” for bushing deflection.

Pics are 100% unloaded with zero weight sucking the spring down… the shackle hanger is in front of the main eye… so if I tack this in place my shackle is going to be inverted.

I measured my springs for the sixth time
Arch length is 47ish and eye to eye straight is 42” so my shackle is actually 1” short according to the formula

Thoughts Wilson and others? Unloaded should the shackle be able to invert or no?
 

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Sometimes a brand new pair of Springs will mess with you making it seem like you need to lay your shackle back then next thing you know you'll get your build finished and all the weight on it and the shackles way too flat, a longer shackle would help you I believe.

I'd suggest tearing down to 1 or 2 leafs and cycling.

I also like to incorporate shackle stops into my hangers. Usually just past vertical so it does inhibit spring movement.



Side note:

What the current consensus on sliders? Seem like everyone was all about him around 5 or 8 years ago but I haven't seen them pop up much and have heard a few people who weren't happy with them.

Edit: I've also heard some talk about tension shackles allowing more travel since you can basically run the shackle damn near 180* it's not exactly easy to package on a lot of rigs, but curious what people think. I know Snowracer has been running that setup for a bit.
 
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YotaAtieToo said:
Sometimes a brand new pair of Springs will mess with you making it seem like you need to lay your shackle back then next thing you know you'll get your build finished and all the weight on it and the shackles way too flat, a longer shackle would help you I believe.

I'd suggest tearing down to 1 or 2 leafs and cycling.

I also like to incorporate shackle stops into my hangers. Usually just past vertical so it does inhibit spring movement.



Side note:

What the current consensus on sliders? Seem like everyone was all about him around 5 or 8 years ago but I haven't seen them pop up much and have heard a few people who weren't happy with them.
Click to expand...
Originally I wanted to try and keep the M38 low so I opted for the shorter shackles as I wasn’t planning on bolting them together to allow a little more side to side deflection without the shackle getting too sloppy in the 5-6” range.

I think the best course of action is to tack it in place as per the formula and adjust from there… it definitely looks trippy as it is… but no engine or 8274 hanging off the front either. I really wanted to cut the frame horns and weld the bumpers on but I guess that needs to wait
 
[memphis] said:
Originally I wanted to try and keep the M38 low so I opted for the shorter shackles as I wasn’t planning on bolting them together to allow a little more side to side deflection without the shackle getting too sloppy in the 5-6” range.

I think the best course of action is to tack it in place as per the formula and adjust from there… it definitely looks trippy as it is… but no engine or 8274 hanging off the front either. I really wanted to cut the frame horns and weld the bumpers on but I guess that needs to wait
Click to expand...

Any reason you can't go through the frame?
 
YotaAtieToo said:
Any reason you can't go through the frame?
Click to expand...
Potential steering box location unless I can use a JK steering box.

I have a lot of options for boxes, YJ (like J10), Toyota outside frame mount rear swing and JK inside mount forward swing
 
[memphis] said:
Potential steering box location unless I can use a JK steering box.

I have a lot of options for boxes, YJ (like J10), Toyota outside frame mount rear swing and JK inside mount forward swing
Click to expand...

Having ran yj's and an ifs Toyota box, there's no way your box will be that far forward.
 
YotaAtieToo said:
Edit: I've also heard some talk about tension shackles allowing more travel since you can basically run the shackle damn near 180* it's not exactly easy to package on a lot of rigs, but curious what people think. I know Snowracer has been running that setup for a bit.
Click to expand...
tension shackles will stiffen up the suspension, in my experience. That might be a good thing with stock YJs or other flat springs.
 
for tension shackles to be effective the spring needs to have a decent amount of free arc.
 
Treefrog said:
Does it seem that it gets stiffer the more the tire goes up and the more horizontal the shackle gets?
Click to expand...
Honestly I do not recall that. I remember from years ago, when converting rear truck shackles from tension to compression, the whole rear spring/suspension seemed to soften up, and axle wrap seemed to get worse too. The shackle length, springs, and pivot location stayed the same, only the shackle direction was changed. I didnt pay much attention to the suspension travel before the change, but suspect the articulation/travel amount didnt change dramatically between the 2.
 
Recently put new leaf springs on and "spring arc length - shackle" was off by few inches. I made provisions for four mounting positions to bolt to.

Lesson learned is that torqueing the u-bolts clamps the spring pack and changes shackle angle vs a free spring.
 
rattle_snake said:
Recently put new leaf springs on and "spring arc length - shackle" was off by few inches. I made provisions for four mounting positions to bolt to.

Lesson learned is that torqueing the u-bolts clamps the spring pack and changes shackle angle vs a free spring.
Click to expand...
So was the shackle hanger positioned too far forward in its free state? Making the shackle too vertical?
 
The loose pack drooped out more and allowed shackle to come to rest on the hanger, horizontal, forward (aka 9 o'clock)
Once torqued, full droop shackle angle is about 10 o'clock, ride height is vertical. Haven't checked bump.
 
rattle_snake pictures would be helpful, so thanks for not posting any...:flipoff2:

So I fucked that shackle formula up, I measured eye to eye, did the math and here is what It looked like with a Chevy 63 and a 6" shackle just bolted up.
IMG_20230121_145926613.jpg
 
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Slander said:
rattle_snake pictures would be helpful, so thanks for not posting any...:flipoff2:

So I fucked that shackle formula up, I measured eye to eye, did the math and here is what It looked like with a Chevy 63 and a 6" shackle just bolted up.
IMG_20230121_145926613.jpg
Click to expand...
This is best for low rider!
 
Provience said:
4: Shackle length: 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.
Click to expand...
So; according to your description, I accidently installed the correct length shackle?
1674753092471.jpeg
 
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