I'm at the stage of putting the springs on my chassis and axels. It's a YJ frame with corp 14, dana 44. I'm using F-150 springs up front and a hybrid ranger main with 3/4 tonne chevy leafs in the rear.
I've welded a legnth of 3x4 tube to the front and back of the chassis. In order to make room for the longer leafs and to gain some wheel base I've attached the front shackle hangers as far foreward on the new bumber as possible and I've used a buggy leaf on the rear as far rearward as possible. I'm getting ready to weld the fixed brackets to the frame in a few days and I want to know how my shackle should rest when there is no load on the Jeep as to know where to weld the fixed mount to the frame.

I know that a fully loaded angle is about 45 degrees. What about just the frame minus the engine/tranny/t-case/tub etc...
I estimate that there is about 1500-1800lbs of gear that will eventuly make its way on to the chassis.

Any suggestions on how to solve my problem here?
Should I go with a 20-25 degree shackle angle and hope that with the extra weight the springs flatten out and increase the shackle angle to 45* ish..... I dunno????
Or should I caculate the angle with the springs at full droop off the chassis?
Thanks...

My shackle angle is 25-30 degrees loaded and it works fine. Shackle angle also has quite a bit to do with shackle length and spring arc- a longer shackle neccessitates less angle and the arch of your spring determines how much forward/rearward movement your shackle will experience as the supension cycles.

I'm using shackles that are 2 inches longer than the stock YJ ones. The springs are basically stock F-150 rear springs.......
It seems that you are supposed to use a longer shackle with the longer springs.......
Ford rears are 56-57" with a 7" offset... They do have a bit of arch ( 2 inches more than the stock YJ springs when put side by side center to center-some of this height is due to the thickenss of the pack also.).....They seem nice and soft but a bit stiffer than the stock springs...

Originally posted by the TJ kid
I'm using shackles that are 2 inches longer than the stock YJ ones. The springs are basically stock F-150 rear springs.......
It seems that you are supposed to use a longer shackle with the longer springs.......
Ford rears are 56-57" with a 7" offset... They do have a bit of arch ( 2 inches more than the stock YJ springs when put side by side center to center-some of this height is due to the thickenss of the pack also.).....They seem nice and soft but a bit stiffer than the stock springs... Yes you should use a longer shackle with a longer spring. Your springs are close to 10" longer than stock YJ, they also have more arch than a stock YJ. The larger arch in conjunction with a longer spring means that you'll have a heck of a lot more length to deal with as the spring flattens- thus you need a longer shackle. I'm not sure eactly how much but I'd guess a little more than 2". Since you're spring is arched and it's travel is not desired in the negative (this is the case with a flat spring) then your shackle will push forward upon compression (vs. rearward with a flat spring). To save yourself some headaches I would set the angle to be around 10-15 degrees unloaded. With load I'm guessing it to come up a bit to like 20-25. This will allow for plenty of movement with your long springs. Should it not be enough and your spring starts to bind or are limited in droop- get a longer shackle. I'm leary of 45 degrees because as the spring compresses the shackle pushes forward, you can theoretically run out of room for your spring to extend if the shackle pushes to enough of an angle and f--k up a spring.

I would tack the mounts in place so the shackles are close to straight up and down, once you get weight on it you can get everything set just right.

Originally posted by bigdude
Since you're spring is arched and it's travel is not desired in the negative (this is the case with a flat spring) then your shackle will push forward upon compression (vs. rearward with a flat spring).

This is true for the front springs with shackles on the front. In the rear the shackles will push rearward on compression. Just making it clear that your explanation is for the front.

Sorry about that and thanks for the clarification:beer:

Thanks guys......I'm gonna take the advice of bigdude and NE-Rocktoy. I'll just tack teh mounts in place to give me a 10-15* un-loaded shackle angle and then move the mounts when the jeep is loaded if need be....
Thanks.........................