leaf spring question

[FINOCJ]

Allright - bit of an odd question that probably can't be perfectly answered given all the variables, but going with approximate gut feeling from those of you with experience in leaf springs on old vehicles (especially CJs or YJs):

How much will the free arch of the spring reduce when under weight of the vehicle as compared to when its just lying on the floor or off the shelf. Obviously the spring stiffness matters the most, but these old jeeps have stiff springs (no flexy softride springs - too narrow and to far inboard for stability). In this case its a pair of superlift (probably pretty stiff) front leafs under an old CJ5 with 6.5" of free arch. Thinking 2-2.5" inches of free arch would be lost when under the weight of the vehicle? more..less?

Also, as the free arch is reduced and the leaf is flattened by the vehicles weight, the straight line eye to eye length (sometimes called the datum line) will increase. Any guess by how much?

My current front leaf springs are too short (or too stiff) as the front shackle sits vertically instead of having a forward angle (in dangers inverting shackle as well as limits droop). Found a pair of supposedly never used superlift 4" lift springs (specifically for early cj) for the front and trying to see if they will work. They are 38" straight line eye to eye just sitting on the floor, which is just less than my distance between spring hangers (38.5"). Under vehicle weight I would like something that flattens to about 4-4.5 inches of arch and lengthens to 40-41" straight line eye to eye.

Sorry I have no info on the true spring length (along the length of the top leaf) but doesn't really change the question even if I did.

thanks all

[CS79bronco]

Can't answer your questions but you might try searching on JP magazine's web site. They and other mags have done stories on springs that might help. Good luck.

[dieseldoc]

well the springs you found should work.
they will stretch the 2.5-3 inch that you are looking for.
the biggest issue I see is you are leaving the front with the forward shackle set up.
this is so not an optimal set up.

on a cj the frame is very narrow and a 2" wide spring. thus why they are so dam stiff.
the yj springs are longer and wider thus the better ride.
as for your ?about the unloaded ach you will lose 40-50% depending on the manufacter.

I used yj spring on my sami I built a custom front bumper with the fixed spring eyes tabs on it, I had to extend thront frame to keep the axle center line right.
to keep it stock position would have needed 2", but as I was after more wheel base I added 7". netting a 4" push forward.
I also used the boomerang shackels I had but modified them from 2" to 2.5". I used a set of very well used 6.5 super lift springs with 3 of the 6 leaves pulled out of the pack. this set up used all but 1/2"up and a 1/2" down of the 14"bilstine 5100 shocks.
flexed very well to say the least. 27" of wheel travel.

look at the spring manufacters specs as you can find the length at free ach and sprung length.

good luck

[FINOCJ]

thanks doc - thinking of pulling one of my current leafs to see how much free arch comes back as well as how much it shortens as a comparison. You think it would be easy to get specs but...good point going straight to spring manufactures (should have thought of that) as I have been going to the retailers for spec info and its never the same.

other points well taken...no concerns with stiff springs given how much highway driving it gets and how narrow and inboard the springs are - stability is good. Some old jeepers like to say the springs may not flex, but at least the open channel frames flex to make up for it (at least until they fatigue and fail/crack).

I actually like the front shackle system - although shackle reversal has its advantages especially off road and with significantly arched springs. But I've also found for highway driving the front shackle is much more stable (tracks straighter with less tendency to 'twitch' right of left when hitting a bump or pot-hole only on one side) which is nice for such a sort wheelbase (only 81" for these early CJ5s) and slightly sketchy steering set-ups (not to mention bump steer). The shackle location has long been a discussion point amongst the jeep crowd - some early military cj5s (m38a1) were factory built with shackle on rear hanger.

Plus you mentioned 2" wide springs...the early ones (pre 76) are only 1.75 inch wide! Gotta love these old jeeps... plus Don't remember when they went wide track but not only are the springs narrower, they are also mounted further inboard in the rear than later CJ/YJs (frame rails step out wider in rear on later CJs and YJs).

cheers

[dieseldoc]

You are very welcome.
pulling a spring is not fun....but might be the only way to get a good idea of what you are getting.
It took me 3 weeks to geet all the messurements and such figured out.
I wish I had some pics of the ting once it was done.

As for the bump steer issue, many manufactures have gone and added a panard bar (trac bar)
To the front ends.
ford did it with the super duties before they want back to the radius arm and coil set up.
may toy and zuk guys add them as the front ends get loose when lifted.
so much changes with different springs.....
I wish dever spring was still here!