# Shackle Flip Theory

Discussion in 'The Garage' started by ARAMP1, Mar 20, 2006.

1. ### ARAMP1Aviator Extraordinaire

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Okay, I’m a little new to the whole lifting via shackle flip, so I have a few questions.

Say I do the normal (as in there are a lot of people that have done it) 4 inch flip. The rear of the spring is lowered a certain amount (over 4 inches) to give the axle a 4 inch drop. However, along with lowering the axle, it also moves it forward. (see illustration) Is this were a longer spring comes in? Also, what about pinion angle?

2. ### mofugly131 ton bucket of rustPremium Member

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That forward movement is negligible. If you do your drawing to scale, you will see the forward movement is not so noticible. I think longer spring=more flex. You can get shims to put your pinion angle back where it needs to be.

3. ### dhcomp3/4 ton statusPremium Member

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you also have to factor change in shackle angle into the eqn.... which reduces the change in axle position

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I went from a 4" rear spring with a 10 bolt stock location. To a 14 bolt FF with a ORD 2.5" shackle flip/ORD zero rate/4"spring with the axle pushed back an 1.5" back,and it's perfect.

5. ### tRustyK5Big meanieStaff MemberSuper ModeratorGMOTM WinnerAuthor

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Shackle angle has nothing to do with the diff location after a flip. The diff's location is determined solely by the front half of the spring. I found that the diff moves approx 1/2" forward after a shackle flip.

To keep the rear tires more centered after a flip I'd use a zero rate to push the diff back a little.

Rene

6. ### jekbrownI am CK5Premium MemberGMOTM WinnerAuthor

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did something about the front of the spring change with a shackle flip? On mine, the shackle, shackly mount etc changed, but the front hanger is stock and unmodified. The word "solely" has me confused here.

As far as the drawing goes, put the lower shackle at a 45-ish degree angle (or whatever ride height will be on your set up) and the amount of axle movement will prolly be less. There is definitely some, but not as much as in the pic above.

j

7. ### miniwally1/2 ton statusPremium Member

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Jekbrown:
The front of the spring stays "fixed" to the frame and thus the spring pivots around the front spring eye. Since the front of the spring "for the sake of this explanation" cannot change length the front to back movement of the axle is controled by the "arc" that the axle moves in around the front spring eye.

You could make a spring with the same rate and axle pin to front eye distance but with a 100' tail and put a 5' shackle on. The postion of the axle under te body of the truck would not change at all in this situation.

8. ### tRustyK5Big meanieStaff MemberSuper ModeratorGMOTM WinnerAuthor

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Thanks Brandon, more clearly put than what I wrote...

Rene

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