Formula for Optimal Shackle Length? (1 Viewer)

[77TLCFJ40]

i have only seen one formula here on MUD to determine the optimal shackle length:

Shackle length = spring length + 1 inch - distance between spring hangers

Can anyone shed more light on this formula or provide a better one?

I am currently running 4" lift springs SUA with 35" tires and +1.5" shackles. My plan is to maximize lift and ride quality without hurting flex. Maximizing droop is more important to me as up-travel (stuff) will be limited by extended bump stops.

Thanks

 

[sadam_husain]

optimal length all depends on the specific setup of how the springs will best cycle through their articulation and what angle your drive line will be in, to maximise droop you want flatter angle shackles that can unload and open up with down travel. Shackles that are long or too long need a brace welded in them to stop them twisting over sideways with the extra leverage

 

[snaggletto]

Not sure about a formula. Just stuff one side, and compress a spring. See if your shackle is swung out to maximum or not. If it is swung out all the way before the spring can start to flatten out then the shackle is to short. Or rather, maybe you would be better to move the spring hanger. Super long shackles affect pinion angle.

 

[White Stripe]

Shoot for a 45 degree angle on the shackle, tack the mount on, cycle the suspension and see how it does. May need to adjust. I have 5" lift springs, I use a pretty long shackle which allows the spring to really move. It uses a lot of driveshaft slip though, and I had to adjust the pinion.

 

[77TLCFJ40]

I appreciate the feedback, but please focus on the original question. Assume the spring and shackle mounts are fixed and the springs are already mounted. The only variable is shackle length. Thanks

 

[sadam_husain]

Assume the spring and shackle mounts are fixed and the springs are already mounted. The only variable is shackle length. Thanks

you'd need a mathematical formula that includes the angle that your propshafts bind, how much travel your slip joints have, the angle of the transfer pinion flanges to keep the U/J's in the same plane and in phase, your ratio of desired up travel vs down travel and what height your bump stops are set at to calculate how long you want to make your shackles

 

[cuteo100]

a lot of trial and error

 

[65swb45]

I appreciate the feedback, but please focus on the original question. Assume the spring and shackle mounts are fixed and the springs are already mounted. The only variable is shackle length. Thanks

Lash

I think you have gotten good responses here, especially from Sadam and White stripe. Optimizing droop will invariably lead to moving either the shackle or the frame hanger. Once you have lifted the truck, the stock mounting points go from being sacred to being a convenience and a compromise. I have cut and moved hangers on two of my cruisers, and have plans to do so on the others as well.

It's all about the droop. I wrote an article about this called the Angle Of The Dangle. Was going to submit it to TLCA for publication. Then I had a huge falling out with them over the raffle truck and just shelved it. I should dig it out and just host it on my website. One of these days.

 

[jim land]

longer leaf spring ( like 60 serie ) give the same result as moving the hanger , it give even more drop and an almost horisontal shackle