Shackle vs. spring lift? - Pirate4x4.Com : 4x4 and Off-Road Forum
 
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Old 02-05-2010, 11:42 AM   #1 (permalink)
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Shackle vs. spring lift?

First post here on pirate. After having been lurking for a couple of years...

I have a '98 Cherokee that currently has 2" of lift via 2" lift coils in the front, and a full length add-a-leaf in the rear. ( I think it's rancho... I bought it with it on it 5 years ago...)

I have 33x12.50x15 BFG AT's on it with a LOT of trimming done to the fenders. (cut too much in the back... stupid pinch weld... I'll weld it back eventually)

I have settled on wanting between 4-5" of lift, and the rest will be trimming and bump-stopping.

After DAYS of searching, I have decided that 2" pucks in the front are just as good for crawling as 4" lift coils, as I'm not going to be jumping the heep anytime soon and the amount of up-travel and the spring rate are just fine at the moment. Granted, I'll have to find a way to keep them from falling out if I flex far enough to unseat my springs, but I'm pretty sure I can find a way to solve that problem. The lower control arms that are on my jeep at the moment are just over 16". This should be fine for a 4" lift as the length of arm recommended for 4" lift is 16 3/8" according to http://www.lunghd.com/Tech_Articles/..._Arm_Chart.htm I'm not too concerned about the roughness of ride that I'll get from 3/8" of difference... Eventually I'll do a long arm to provide more articulation but that takes $$$ and I really don't have much (school is expensive).

My real dilemma is what to do in the rear. I have a set of 2" lift shackles nearly made, but I came across a set of 4" lift springs on craigslist the other day, and that started me thinking...

It seems to me that using lift springs really only adds to the stiffness of the ride, and basically functions like a lift block except with more lateral support to limit axle wrap, and decreasing the torque applied to the main spring by decreasing the length of the lever at the axle end. To the best of my knowledge the cause of axle wrap is the torque applied by the twisting of the axle under load. when you use a lift block you increase the length of the lever which increases the amount of torque applied to the spring. This is the major disadvantage to just putting a 4" chunk of metal under the springs and using larger u-bolts. The other disadvantage to using leftover metal from your last project for a lift is that it doesn't actually give you any more usable suspension. As near as I can tell all that it does is move the chassis of your vehicle higher over the axle. This can give more clearance for bigger tires by allowing the tire to pivot more before entering the wheel-well, allowing your tires to actually go into the wheel-well before hitting the outer body panel or fender flare. However, this doesn't provide any more articulation of the suspension. You don't get any more up or down travel out of your suspension, you just stop spashig body panels and cuting those expensive tires. In essence it's a body lift.

Using lift springs alleviates the axle wrap problem by adding more leafs to the pack, each with a decreasing length. This causes only slightly more torque to be applied to the mainspring than stock and therefore spring-wrap is less likely. Other than that, from what I can tell it's really about the same as using a lift block. You are just moving the vehicle higher over the axles and not providing any more articulation. The Up-travel will be limited by the spring rate (which is usually increased in lift spring packs and/or by using an add-a-leaf), as well as the length of your shackle and it's relative starting angle/position.

Using a shackle lift doesn't increase the torque applied to the main leaf. And if your are using a longer shackle you are increasing the amount that the leaf spring can "change length." This allows your axle to have more up or down travel (depending on the starting angle) but not both. It seems to me that using a lift shackle is the only way to actually increase the amount of travel in your rear axle. The other lifts are all just gimmicks to get us to spend more money.

There are limits though. With axle drop comes problems with pinion angle and binding at various other places, along with the problems associated with the slip yoke at the transfer-case. Using a shackle based lift will also cause more torsional stress to be applied to your springs (twisting) and may wear them out faster.

Ok, so that was an incredibly long explanation of what I think I know in order to just ask this question:

To add 2" more lift to my jeep that is actually usable the shackle lift is the right way to go right? Or did I over-look something with the lift spring pack?

Are there other factors to consider?

I know that I'll have to shim my axle with 3.5-4 degree shims so that the pinion angle is correct.

At 4" of total lift according to the guys at Teraflex I will be at the MAXIMUM before I HAVE to do a SYE, and my shocks should still work. I should be able to get by for awhile.

Is there anything I missed? I know I could just put the shackles on and call it good, but all of the little things add up, and when you are already eating Ramen, and it's your daily driver, you want to be sure.

Any help would be appreciated...
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Old 02-05-2010, 03:29 PM   #2 (permalink)
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Unless they're being used to fix a high shackle angle, I vote a big NO on the shackle lift. If your shackle angle is good now, your lift shackles are more likely to hinder your flex, not improve it.
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Old 02-05-2010, 04:22 PM   #3 (permalink)
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Lift Shackles =

They bring about more problems then they solve.
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Old 02-05-2010, 06:42 PM   #4 (permalink)
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Quote:
Originally Posted by The Black Sheep View Post
Lift Shackles =

They bring about more problems then they solve.
Agreed. However, boomerang shackles set up with correct angle and proper springs is quite impressive.
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Old 02-05-2010, 07:43 PM   #5 (permalink)
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Agreed. However, boomerang shackles set up with correct angle and proper springs is quite impressive.
I will concede that that can work well in the rear. NEVER in the front though.
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Old 02-06-2010, 02:53 PM   #6 (permalink)
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Lift Shackles =

They bring about more problems then they solve.
Such as???
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Old 02-06-2010, 05:18 PM   #7 (permalink)
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boomerang shackles

Why shouldn't Boomerang shackles be used in the front?
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Old 02-06-2010, 07:42 PM   #8 (permalink)
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Why shouldn't Boomerang shackles be used in the front?
Nothing is wrong with boomerangs in the front. Most boomerangs at most add less then 1/2" of lift or no lift at all. Boomerangs=/=Lift Shackles. I like boomerangs personally.

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Originally Posted by Handycapt View Post
Such as???
Steering issues. Lift shackles always point the pinion up, which creates negative caster. Ontop of the that, they allow for more chassis/body shift when steering, which makes steering sluggish and bumpsteer becomes more of a problem, all that ontop of any caster issues. I ran them for a maybe a year while trying to figure out while my junk was driving like shit when I was younger and once I learned a little more and took them off (after I installed TJ flares and didn't need the extra lift) I was amazed at the difference. I will never run them again, nor will I recommend them to anybody. Someguys even take it to extremes with crazy shit like 8" shackles....stupidity.

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Old 02-08-2010, 08:05 PM   #9 (permalink)
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Steering issues. Lift shackles always point the pinion up, which creates negative caster. Ontop of the that, they allow for more chassis/body shift when steering, which makes steering sluggish and bumpsteer becomes more of a problem, all that ontop of any caster issues. I ran them for a maybe a year while trying to figure out while my junk was driving like shit when I was younger and once I learned a little more and took them off (after I installed TJ flares and didn't need the extra lift) I was amazed at the difference. I will never run them again, nor will I recommend them to anybody. Someguys even take it to extremes with crazy shit like 8" shackles....stupidity.
We are talking about putting lift shackles in the REAR of my Cherokee. There can't be any caster issues, because there is no steering pivot in the rear end. There is no steering at all. Actually, any steering issues shouldn't arise at all. I already removed my rear sway-bar, and I didn't notice any steering changes. In theory that allowed far more chassis/body shift to occur than the lift shackles will. In theory at least... Although depending on the shackle angle it can have an effect on the spring rate of the leaves, which I suppose if I get it wrong would allow for more body roll when cornering if I made them softer.

Or am I totally wrong?
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Old 02-09-2010, 04:26 AM   #10 (permalink)
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Originally Posted by Handycapt View Post
We are talking about putting lift shackles in the REAR of my Cherokee. There can't be any caster issues, because there is no steering pivot in the rear end. There is no steering at all. Actually, any steering issues shouldn't arise at all. I already removed my rear sway-bar, and I didn't notice any steering changes. In theory that allowed far more chassis/body shift to occur than the lift shackles will. In theory at least... Although depending on the shackle angle it can have an effect on the spring rate of the leaves, which I suppose if I get it wrong would allow for more body roll when cornering if I made them softer.

Or am I totally wrong?
I won't deny that I ran my rear shackle lift longer then my front. This was to clear my miltary wrap from hitting the frame until I realized that the extra spring wrapped around the shackle side was worthless and doing nothing, as it's the hardmounted spring hanger side that makes a difference.

I noticed the torque steer and ass end wiggle when getting on and off the gas was a little more pronounced in my rig with the rear locker on the road, nothing.

And no, longer shackles will not affect spring rate. Spring rate is entirely to do with spring, the shackle doesn't influence it at all. Now alot of people believe they influence the travel a little, but in all honesty between physics, geometry, and personal experience, lift shackles don't do anything to increase wheel travel. All they do is add 1/2 the lift of the increase in height over stock. So if you are running a shackle thats 2" longer then normal, then you gained about 1" of lift depending on wether or not your axle is in the center point of your leaf springs. Hope this makes sense.

In conclusion, if you want to run them, run them, decide for yourself. I didn't like them, knowing what I know now. Just remember check your pinion angle afterwards, if you are using shims you will probably have to shim down a degree or 2 to get things back to where they are supposed to be.

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