A moderate lift shackle is alright in most instances. But to use a moderate to long shackle regardless when used with a stock worn out sagging leaf is not. And that is what I am pointing to. Most responses on here or other posts are talking about worn out sagging leafs and a lift shackle to lift or compensate. At that point a leaf is already compromised.
The shackle increase in length causes the pinion angle to be increased which is a bad thing.
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.
It rotates the axle down at the shackle side of the spring.
It increases pinion angle
It increases leverage on the shackle mount
It increases droop (down) travel
It decreases approach/departure angle
It adds lift to the suspension in the amount of half the difference between the new shackle and the original shackle.
A shackles length can dictate overall travel, both droop and compression. Stock Xplorer leaf springs sit pretty flat with the load of the Xplorer 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.
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.
This is not meant to be a debate or argument at all. Just my experience with others and my point of view. Most on here are all to fast to say to another asking for help to just slap on a extended shackle, and or go and make yourself one, or go to a local auto store and slap one on. Warrior daes make a beefy shackle, granted. But, that being said, it is not the best solution in my opinion. And that is just it, my opinion through experience with others.