Shackle lift pros and cons
 

tell me your opinion of using lift shackles. known problems etc

I know that when used in the front it can cause pinion angle problems. That's why all the lift kit comes with the front spring hanger, to drop the front of the springs the same length that the shackles lift it in the rear. In the rear of the truck, I think it should be fine. I need to start looking at that myself.

4Crawler - Does a shackle "lift" move the axle forward or backwards at all?

Generally not, since the front end of the spring is attached to the frame and the axle is attached to the center of the spring, that length is not going to change. What might change a bit is if you say had a shorter shackle that was angled backwards to a great angle and a longer shackle was installed, the shackle angle would be a lot less so you'll have less rear-ward movement of the axle under compression.

You can do longer shackles and just buy the pinion angle shims to correct it as well.....