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  #1  
Old 7 Oct 2008
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Do lift shackles cause a stiffer ride?

I should know the answer to this (and thought I did) but there seems to be a few different opinions. I put 4" lift shackles (for about 2" of lift) in my leaf-sprung TCL at the same time as having new mains and add-a-leafs installed. Now she rides like she's on concrete.

I know the new springs would stiffen things up, but what about the shackles--do extended shackles change the spring rate, and would reverting to the stock shackles take out some of the stiffness?
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Old 7 Oct 2008
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The shackles shouldn't make any difference to the ride stiffness, that'll just be down to the add-a-leaf's and new main springs.
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Old 7 Oct 2008
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I agree with Jim,

Now you have the stiffer and additional leaf, there is your concrete.

The longer shackles won't add any harshness to the ride at all.
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Old 7 Oct 2008
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Thanks - time for a seat cushion then!
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Old 7 Oct 2008
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Yup - as longer shackles should allow the spring to flex more, then longer shackles should in theory give a more compliant ride. What about removing some leaves and fitting firestone "ride-rite" airbags. Give you the ability to carry weight and also retain decent ride when not laden up?
G
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Old 7 Oct 2008
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If lift shackles are installed at the front of the front axle of a TLC they decrease the caster angle and make steering a straight course very difficult. This can be corrected by installing steel (NOT aluminum - it rots) caster wedges between the spring and spring bottom plate (the one the U-bolts go into). Make sure the spring through bolt attaches to the wedge. The precise size of the wedge depends on the measured caster change, but it can be calculated using simple geometry.

Charlie
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Old 11 Oct 2008
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4WDTraveller: Extended shackles should not affect ride quality unless they meet the spring at an improper angle. The angle between spring and shackle should be close to 90 degrees, to allow the spring to flex properly in both directions. If, for example, the rear shackles lean in toward the spring, creating a very shallow angle, they could very well contribute to reduced compliance over harsh bumps. In extreme cases this can also cause the shackle to invert and lock against the chassis.

I'm curious as to why you installed add-a-leafs with new springs? I am not a fan of them - I've seen at least a dozen broken examples, albeit usually from leafs that were added to already sagging springs in an attempt to extend their life. The add-a-leaf is under too much stress in such situations. I suppose an add-a-leaf that was engineered along with a new set of springs would be okay, but why not just design the spring pack for the required lift to start?
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Old 11 Oct 2008
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[quote=OJEditor;210513]4WDTraveller: Extended shackles should not affect ride quality unless they meet the spring at an improper angle.

quote]

They will cause a change in caster which definitely affect driveability and handling. In the front.

Charlie
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Old 13 Oct 2008
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Charlie, different question, but yes, you're right of course, at least after a point. I have OME anti-inversion shackles on the front of my FJ40. They are somewhat longer than stock - perhaps an inch? - and I need no shimming or other compensation. The vehicle still drives and handles perfectly. Any longer than that on the front is asking for trouble.
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Old 13 Oct 2008
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Quote:
Originally Posted by OJEditor View Post
Charlie, different question, but yes, you're right of course, at least after a point. I have OME anti-inversion shackles on the front of my FJ40. They are somewhat longer than stock - perhaps an inch? - and I need no shimming or other compensation. The vehicle still drives and handles perfectly. Any longer than that on the front is asking for trouble.
Yes, having the lift shackle in the front of the front spring rotates the axle forwards (lifts pinion bearing upwards). The angle can be calculated as ((extra length of lift shackle)/(total length of leaf spring)) X 57 degrees (times -1 for lift in front).
In other words (remembering the polynomial expansions for trigonometric functions), sin x ~ x for small angles, x being of course stated in radians, not degrees. 1 radian = 360/2 pi ~ 57 deg.

Leaf sprung Landcruisers are set at ~ 1 deg. If you have a 46" spring and 1" extra shackle length, change in caster ~ -1.3 deg, which takes you slightly into negative area. Remember that if the kit advertises "1" lift" it's a 2" longer shackle which will change caster ~-2.6 deg. For that I'd install at least 3 degree caster shims. Steel, not aluminium!!!!
Steering with negative caster can best described as "squirrelly".

Charlie
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Old 13 Oct 2008
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Bloody 'ell, you're clever.
No joke.

I know what "squirrelly" is, but as for the rest of it.......
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Old 13 Oct 2008
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Charlie, that sounds about right from calculation. I'd expect that much change could be noticeable in driving, but on mine at least there's no degradation at all in straight-line stability, nor any increased tramlining.
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Old 15 Oct 2008
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Originally Posted by OJEditor View Post
4WDTraveller: I'm curious as to why you installed add-a-leafs with new springs? I am not a fan of them - I've seen at least a dozen broken examples, albeit usually from leafs that were added to already sagging springs in an attempt to extend their life. The add-a-leaf is under too much stress in such situations. I suppose an add-a-leaf that was engineered along with a new set of springs would be okay, but why not just design the spring pack for the required lift to start?
Short answer: to save a couple bucks. I should have gone with new spring packs; add-a-leafs aren't the answer. Plan now is to pull off the lift shackles and source replacement springs. I'm also downsizing the tires to 31"s from 33"s.

Longer answer:
Getting (re)Sprung for Spring
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