All about shackles
I hope you packed a lunch, this could take a while.
It would seam that there is alot more interest lately in lift shackles than in the past. I'm not sure why, but in the last week alone there has been 10 new threads on the subject, as well as just shackles in general.
Well, I am by no means an expert in the subject of shackles, however I have done my homework. I've made several hundred sets of shackles in the past and have helped dozens of people via PM and email (both from this board and elsewhere) with their installation and issues that come up. Sometimes I feel like tech support. :laugh:
I have installed shackles ranging from 1/2" drop (yup, 3" bolt to bolt) to 2" of lift (OMFG!!) on my rig and on others for testing purposes, road use, offroad use, and just all around general "hey, wonder what would happen if.." use.
During all this time I've had to do quite a bit of research, question asking, problem solving, etc. So I decided to start this thread listing all sorts of useful information that can be found by people when they search. I'll update it as new information comes available and I ask that anyone else out there that sees something I omit to please speak up and add it to this thread.
There will be some cut-n-paste from varying sources, and I wish I could give credit where it is due but I am not the type of person to save links I find, rather I just take that information and concatenate it into a big ol' text file that I keep in my home directory (similar to "My Documents" for all you Windows folks).
So with all due respect to those who have made this information available previously, here goes:
What do we need shackles for in the first place?
Simple, to allow for length changes of a leaf spring. A leaf spring suspension is a pretty simple thing, leafs position the axle under the vehicle, and supports the weight of the vehicle. As a leaf spring flexes up or down, its length from eye to eye changes. Since one end is mounted solidly, and cant move, all the length change happens at one end, which has a shackle between the spring and frame to allow for movement.
What are the pros/cons of different shackle lengths?
In relation to stock length, there are a bunch of things affected when you change shackle lengths.
A longer shackle will move one end of the leaf spring further away from the frame, doing several things.
How do longer/shorter shackles affect wheel travel?
Bear with me here, this digs a little deeper into how leaf spring suspensions work. To start with, a shackles length can dictate overall travel, both droop and compression. Let's start with the leaf spring. Stock jeep leaf springs sit pretty flat with the load of the jeep on em, not so with lift springs since they have a larger arch in order to provide that lift. Since lift springs are designed to bolt in with no changes to the mounts, the eye to eye dimension of the spring is the same as stock, but with the additional arch, the main leaf of the spring pack is actually quite a bit longer. So, in order for a lift spring to compress all the way to being flat, the eye to eye dimension is going to be greater than the stock spring. If the shackle is not long enough to allow this to happen, the spring will bind before it gets flat, if force is applied after this bind point, the spring pack will flex into a W shape, fatiguing the springs and shortening their lifespan.
How a shackle affects droop travel is a bit easier to picture. When a spring droops, it will do so until its eye to eye dimension is limited, it hits this limit when the shackle is in line with the arch of the main leaf of the spring. A longer shackle will allow for more droop travel since when it reaches the max droop angle, the shackle end of the spring will be further away from the frame then it was with the stock length shackle.
Now we get to figure out just how long a shackle needs to be to work properly with our suspension setup.
Its best to start this while actually installing a lift, or whatever other work you may do that involves taking apart your suspension. Get a length of string, any ole string will do, its just going to be our measuring stick for this operation. Tie it to the fixed spring mounting bolt, good and tight so it wont come off. Now, lay the string along the main leaf of the spring so it follows the arch. Mark the string where the shackle bolt would pass through the spring eye. You now have the total length of the main leaf. Pull the string tight, and rotate your shackle forward and see if it reaches the mark you made for spring length at a 45-50 degree angle. If it doesn't, then measure from the mark on the string to the shackle mount, and this is how long you need the shackle to be for your suspension. Be aware of the other things a longer shackle will do to your suspension, and be able to account for them when you make the change.
What the heck is shackle inversion, and why is it a bad thing?
Shackle inversion usually happens on the front of jeep YJ's and CJ's when the suspension is drooping to its maximum point. As we discussed earlier, this is when the shackle is in line with the arch of the main leaf of the spring pack. While at this point, if something hits the shackle while moving forward, its possible, and probable, that the shackle will fold backwards instead of returning to its normal position when weight is put back on the wheel. The shackle folding back against the frame, shortens the eye to eye length of the spring, possibly bending it. Shackle inversion is usually pretty simple to remedy, a lever of some kind is used to pry the shackle away from the frame and past the point of max droop, and then the spring will do its job and spring back to where it should be. Be careful tho, as the spring attempts to spring back, it has some stored energy that will be released pretty quick like, possibly taking your lever and throwing it into the woods. Shackle inversion can be avoided by installing stops on the frame to limit the shackles travel, or designing a stop into the shackle itself. Some folks use boomerang shackles in the front with the short leg at the frame end so that the center brace acts as a stop, but its not what boomerang shackles were designed for, we'll get to that in a minute.
Why do some shackles have braces welded in while others don't?
Bracing between the two sides of a shackle can help or hurt, depending on what your goals are. To explain we'll have to go back to how a leaf spring works a bit more. As the axle attached to the springs articulates (one side in compression, the other side in droop), the spring still has to do its two jobs, locating the axle, and supporting the weight of the vehicle. As the axle twists, the springs must change length, as well as twist with the axle. That's the reason for rubber or polyurethane bushings in the spring eyes, they allow the spring to twist in relation to the bolts holding it in place. While this twisting is taking place, the sides of the shackle will also move a bit in relation to the spring, one side being slightly ahead of the other as its pushed by the bushing. Adding a brace (or a bolt with sleeve) between the two sides of the shackle will stop the shackle from twisting forcing the bushing to do more work, and transferring some of the twisting force to the shackle mounting point on the frame. Remember I said a shackle brace can help or hurt depending on your goals? If your goal is road handling like a sports car (don't know why you would want this from a jeep, but whatever), then the brace is a good thing as it will help to firm up the suspension as the body rolls around corners. If your looking for the last bit of available wheel travel, then the solid braced shackle can hurt a bit. When is a braced shackle really needed? When the shackle length increases over about one inch over stock. As the sides of the shackle get longer, they will flex between the bolts as force is applied to them, adding a brace will reduce this flex, which can be a huge negative with long shackles, as they induce a vague feeling to the handling and allow the springs side to side movement to increase.
Now on to shackle shapes, and how they affect things.
Up until a few years ago, shackles were simple, strait pieces of metal, then came the tow shackle, and the boomerang shackle. The tow shackle is pretty simple, still 2 pieces of metal, but provisions have been made to allow the hookup of a tow bar for flat towing. Sometimes they are run backwards so that the tow bar attachment point is towards the axle of the vehicle, and with the pin installed will act as a shackle stop to reduce the chance of shackle inversion. The boomerang shackle was origionally designed for the rear of YJ's. In the rear of YJ's with lift springs, as the suspension compresses, the longer length of the main leaf and the added travel the shackle has to account for it would cause the shackle to contact the rear cross member limiting travel. Back in the day, before boomerang shackles, we'd just notch the crossmember where the shackle hit and things would be good. The boomerang shackle was just a bit more BLING way of getting around the problem. Boomerang shackles are also used by some in a front application with the short leg towards the frame to counter shackle inversion. Some mistakenly think that the different shape of the boomerang shackle will alter the angle of the shackle or how it travels through its range of movement. This is not true, the shackles angle is measured in a strait line between its mounting points, it can be a boomerang, zig zag, strait, or round, the shape does not change the angle of the shackle. On an unrelated note, this is why bent drag links and trac bars don't change bump steer, the mounting points dictate the angle, not the shape of the bar.
More to come....
The angle of the shackle can stiffen or soften a spring's normal rate. You can determine the effective angle of a shackle by drawing a line through the middle of both spring eyes and a line through the shackle pivots. Then measure the angle formed by the two lines. You can increase the effective rate of a leaf spring by decreasing the shackle angle. An increase in shackle angle will produce a decrease in the effective leaf spring rate of a leaf spring.
A good starting point for shackle angle is 90 degrees. In this position the shackle has no effect on spring rate. Keep in mind that the shackle angle changes (and consequently the spring's effective rate changes) whenever the suspension moves. Also, the shackle's angle will change whenever you change the chassis' ride height, the arch of the leaf, the load on the leaf, or the length of the shackle. Since the shackle direction changes when the leaf is deflected past a flat condition, you should avoid deflecting the right rear leaf to an extremely negative arch condition. This could cause a very large shackle angle at high loads and consequently a very soft spring rate. Excessive body roll and poor handling could result. You can correct this problem by decreasing the shackle angle, increasing the arch, of the spring by increasing the rate of the right rear leaf spring.
Shackle length is another factor affecting the rate of a leaf spring. A short shackle will change its angle (and the effective rate of the leaf spring) quicker than a long shackle upon deflection of the leaf. There is a second shackle effect on the stiffness of the rear suspension that counteracts and sometimes exceeds the shackle?s effect on spring rate. This second effect occurs whenever the shackle swings in its arc and moves the rear spring eye vertically.
The vertical movement of the rear spring eye causes a jacking effect. If the shackle movement forces the rear spring eye downward, the leaf will deflect and exert an upward force on the chassis that will add stiffness to the rear suspension. Conversely, the shackle will reduce suspension stiffness if t causes the rear spring eye to move upward during suspension travel.
The stiffening effect occurs during suspension deflection whenever the rear spring eye is ahead of the upper shackle pivot and the shackle is moving rearward. In this position, however, the shackle also produces a softening effect by reducing the effective rate of the leaf spring (due to the large shackle angle). The overall effect to the stiffness of the rear suspension is determined by the greater of the two shackle effects. Under opposite conditions, you can expect a reversal to the above effects. If the rear spring eye is located behind the shackle pivot the shackle effect will tend to reduce suspension stiffness whenever the shackle moves rearward. However, the small shackle angle will tend to stiffen the spring's rate. The overall effect to the suspension's stiffness is determined by the more dominant of the two shackle effects. Keep in mind that the movement of the rear spring eye (from its static position) is mostly forward under racing conditions.
If a leaf goes into negative arch the travel direction of the shackle changes and the shackle effects change. Handling is not consistent under these conditions.
The second effect of the shackle can be enhanced by increasing the length of the shackle. Generally, the second shackle effect (jacking)is dominant.
My next post will be on shackle installation - at least the way I do it and the things I have come across.
My little boy is "gone fishing" in my aquarium right now so I have to get after him. :laugh:
great job brandon! this is a great read... though i'm only half-way done with it... i wanted to show my appreciation first... hope the second half doesn't disappoint... surely it won't.
EDIT: apparently there are two second halfs ... the second post is a mirror of itself
Wow, Brandon, this is great! well done!:cheers2:
Added to the FAQ.
I'll fix it right now.
wow well said.
i have a 2" shackle lift on my jeep and it good for the look and the clearance but the one thing i dont like is that anytime i try to climb a hill or a mound of some sort the shackles dig in. :(
but other than that there great.
Installing shackles is probably the easiest suspension work there is to do - assuming you have the right tools.
Below is the procedure I use when installing new shackles. I've done it enough that I can do all 4 corners of the Jeep in less than half an hour, depending upon how much beer is involved.
Graned, you can probably get by using less or more tools than listed here, which will make the job more difficult or easier respectively.
2 sets of jack stands (4 total)
A floor jack
A bottle jack
3/8" or 1/2" ratchet
3/4" socket that fits the ratchet
And do I even need to mention, Blaster's PB? (commonly called PB Blaster)
Sometimes a cutoff tool (such as a wheel or sawzall) is necessary.
Start the day before, or two days before, or depending on how bad your rust issue is, a week before. Spray all the contact points where the nuts meet the bolts. Do this once or twice a day for however long you find it necessary to get bolts unstuck from your Jeep.
When time comes to do the deed, start with the front (it's the easiest) and do one side at a time.
Start by breaking the bolts/nuts free while the Jeep is still on the ground. Use the wrench to hold the nut and use the breaker bar if necessary to break the bolt free. If you have an impact gun this will be much easier.
Jack up the Jeep until the suspension of hanging and the tires are off the ground.
Place jack stands under the frame to support the jeep.
Now place the other set of jack stands under the axles to support them. Some people find it easier for them to just use the floor jack to hold the axles, but I believe is redundancy (safety first).
If you plan on cutting the bolts out because you have new hardware, now would be the time to do so, since there is no compression on the springs.
Now that the bolts are broken free, and the suspension has no compression on it, go ahead and remove the shackle-spring bolt. The is the bolt that connect the spring to the shackle.
Once the shackle-spring bolt has been removed, remove the shackle-frame bolt. This is obviously the bolt that connects the shackle to the frame.
The reason I remove the shackle-spring bolt first is that I have found that if a problem crops up, it is usually with the shackle-frame bolt.
OK, now you should have the shackles off and the bolts removed. In *most* cases the shackle-eye of the spring has curled up towards the frame, this is more common than it hanging lower (which happens on old stock or sagged springs).
The installation is pretty straight forward. Start by installing the shackle-frame end of the shackle first. But do not torque it down to specs just yet, just get it on there pretty good, a little side-to-side slop will help get the spring into the shackle easier.
As mentioned before, in most cases the spring has curled up towards the frame. This is where the bottle jack comes in to place. You can place it between the spring and the frame itself to force the spring down so that you can line it up with the new shackle. If you do not have a bottle jack you can use the jack under your hoot, or a pry-bar, or have a very heavy friend stand on it. :thumbsup:
If the spring is hanging too low then go get some new springs! :laugh: Or put the bottle jack or floor jack under the eye of the spring to bring it back in place. If you have to do this you'll need to place the jack up on blocks or something. The only two times I came across this I used a bottle jack on a cement block.
Once you get the spring eye lined up with the shackle, insert the bolt and tighten it down.
Now move on to the other front end shackle and repeat the process.
Once both shackles have been replaced lower the jeep off the jack stands, and then tighten the bolts down to the proper torque specs, or whatever torque specs you find necessary. For my shackles I tightened the shackle-spring and shackle-frame bolts to 40 ft-lbs and the center support bolt to 45 ft-lbs. At least that is where they are now. ;)
Next post will be about doing the rear and the fun of getting the shackle-spring bolt out, which I'll post in a little while, have more "daddy things" to do right now.
Brandon, thanks a ton!
Two questions... I have 1 inch+ lift shackles on a 4" procomp lift. There is a brace (bolt w/ sleave) ... you mentioned there may be better travel off road without the brace... can I just take it out and not worry about weakening the suspesion too much to compromise saftey on the road?? Under twisting of going over obstacles, won't this overstress the bolts holding the shackle to the spring and mount?
I am looking for better articulation if I can get it... the procomp springs that hold up this v8 converted YJ are stiff!
Second question is a dumb one... but I'll ask it anyway cause you can't see me blushing... but with the boomerang shackles on the back.. should the pointed part face out the back of the jeep like < or should the point face forward into the jeep like > ???
...Continued from above.
OK, now where was I? Oh yes, on to the rear!
Replacing the rear shackles
Now that you have your front shackles replaces and torqued to specs it's time to move on to the rear. It's pretty much the same dog and pony show, with a twist! And we all love twists don't we?
So... break loose the bolts, get the Jeep frame up on jack stands, allow the suspension to drop, and put jackstands under the axles.
Remove the shackle-spring bolt first (same as with the front), and now the fun begins!
Jeep engineers had to be having a laugh when they designed the shackle-frame bolt to go in the way it does. Because (at first sight) you have to drop the gas tank just to get the bolt out. Just to get one damned bolt out!! Yup, if you try to pull it straight out it comes into contact with the fuel tank before it comes out enough to clear the bushing/sleeve in the frame.
Well, alot of people throughout the years just broke out their favorite cutoff tool and made quick work of that bolt, others actually went through the process of dropping the tank to do it - which can sometimes be a good thing because this allows you to replace the fuel pump, sending unit, sock filter, or anything else you might have been putting off because you didn't feel like dropping the tank. But there is another way!
Yup, that's right, another way - that takes a little time, patience, and... did I mention time? ;)
Here's how to get those top bolts out.
First, take the nut off the bolt!
Now, force the bolt out as far as you can. You'll probably need to use a punch and hammer to push it through because it might be pretty tight. A screwdriver will work in lieu of a punch.
Now that the bolt is pushed through as far as it can go, get some needle-nosed pliers and a small flat head screwdriver and try to get that sleeve out of there. This is the part that takes some time, but after you do the first one, doing the other side of the Jeep is a snap because you already know the tricks needed to do it. I have done this so many times for other people that I made a special tool to do it. It's an oversized threaded rod that I force into the sleeve, then I heat it up and just pull the sucker out. Heating the rob causes it to swell a bit and since I had to force it in there it is tight already. Add that to threading on the rod and it makes for some nice grippers... anyhow.
Where were we? Oh yeah! Now that you have the sleeve out, pup that half of the bushing out. In case you didn't know, the bushing is a 2 piece, now that I've told you that you are probably slapping your forehead right now going, "duh!" Once you get that half of the bushing popped out you are on the home stretch.
You will notice how the bolt has some wiggle room now, a whole lot in fact. If you're lucky you should be able to force the bolt down and out. If you're having too much trouble doing that, try pushing the bushing that is still in there out an inch or two by inserting a screwdriver in the other end of the tube where you just pulled the first half of the bushing out. Once you get a little bit of the remaining bushing out it allows for the bolt to smush the rubber more and gain an even steeper angle to pull it down and out.
If all that fails, just do whatever you feel like doing then. Cut the bolt, torch the bushing into nothingness, beat your neighbor with a steel pipe - whatever makes you feel better so long as you get that bolt out.
You can always drop the gas tank if all that fails. ;)
Well, the rest is pretty much self explanatory. Just put it all together, drop the Jeep, and torque the bolts down to specs.
And there you have it.
Off road I don't think it is as big of a deal due to low speeds. But on road, at higher speeds, there is a good amount of stress on those longer shackles - especially when cornering.
But like I said - no personal experience in that manner.
^See that? That's how your shackles should look. The front and rear are bass-ackwards from each other.
Up front, the longer leg of the shackle connects to the spring and they "point" rearwards (towards the Jeep)
In the back, the shorter leg of the shackle connects to the spring and they "point" forward (towards the Jeep).
Great advice... can I ask a few more questions? The shackles I put on may have more than 1 inch of lift, measuring bolt to bolt in a straight line, the fronts are about 5 7/8" center of bolt to center and the backs are about the same. The front shackles are straight and almost verticle at normal stance with the spring end slightly ahead of the mount end. I didn't really realize when I put them on that they would lift the jeep... and may have lifted it about 1.5 -2 inches. The shocks are more at the top of their range and the rear drive shaft slipped out about 1/4 to 3/8ths more than original....
So, questions... what would be your recommendations for no lift shackles?
Again I have those stiff procomp springs that I wouldn't mind changing out for less stiff but don't know which are best for a sbc v8 converted w/ a auto trans winch on the front etc...
so second question... which leafs would you recommend?
Third question... I have been thinking about a front shackle reversal kit... got any recommendations on that? Again, I really don't want a bunch of lift, and I do have a good welder if some welding is needed.
I just thought if I'm replacing the shackles... I might as well replace the springs and convert the front all at the same time...
Thanks again for your time and help with this!
89 YJ, 4" in procomp lift, 2" body lift, SBC V8, 700R4 trans, Ford 9" rearend, original dana 30 front, 4.11 gears, 33" tires, warn winch, full size spare tire & Jack on after-market carrier, ARB lockers front & rear... LOVE IT!
It is common for a slip yoke drive shaft to poop out more when you lift the vehicle (either via shackles or springs), s don't worry about that.
And if I'm interpreting what you wrote correctly, then your shackles are sitting correctly. A picture would help though.
As for the shocks, you seem to be in need of longer ones. They are more than likely limiting your spring travel.
OME, BDS, and RE make springs for "heavier" Jeeps, and their performance are something to be had.
Oh, and Superlift also has a 3.5" lift kit with "heavy duty" springs.
IMO they are great for a street only Jeep due to the added comfort they give, but not a good investment for offroad performance - $300 can be spent on better things for offroad.
Depending on the tire size you like to run, you might be able to step down a bit on your lift. With a 2" body lift and 33" tires you can put a 2.5" suspension lift on there and have no rubbing issues. But the springs better be the heavy duty ones due to all the added weight.
But all things depend on how much money you have to throw at it.
Ideally, if I had your rig I'd be running a 4.5" RE heavy duty lift kit with a 1" body lift and 33s... but that's me.
Oh... and you're welcome. ;)
I replaced my shackles this morning. Here are some pics from the removal and replacement. The sissor jack wedged in between the leaf springs and the frame is the trick and makes this job easy. I use the sissor jack to pry the leaf spring until the tension on the bolt holding it is gone. Then just pull the bolt out.
Brandon, thanks again for the great shackles and quick turn around! You da man.
<a href="http://s417.photobucket.com/albums/pp255/carl6405/?action=view¤t=DSC_0003.jpg" target="_blank"><img src="http://i417.photobucket.com/albums/pp255/carl6405/DSC_0003.jpg" border="0" alt="shackle replacement"></a>
<a href="http://s417.photobucket.com/albums/pp255/carl6405/?action=view¤t=DSC_0002.jpg" target="_blank"><img src="http://i417.photobucket.com/albums/pp255/carl6405/DSC_0002.jpg" border="0" alt="shackle replacement"></a>
<a href="http://s417.photobucket.com/albums/pp255/carl6405/?action=view¤t=DSC_0005.jpg" target="_blank"><img src="http://i417.photobucket.com/albums/pp255/carl6405/DSC_0005.jpg" border="0" alt="shackle replacement"></a>
And it looks MUCH better with the smaller shackles on there man.
You're welcome! :thumbsup:
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