Leaf Springs

[thorjeep]

I used my buddies '92 YJ Springs when I did a SOA 18mos ago. They settled to being flat across, now after the Rubicon, they are bowed down.


I would like to NOT get any lift on new springs, and keep the ride soft. I have 35" MTRs on now, and I am happy with them, if I go bigger, I will go wide.

Question is, which would be better, re-curving the current springs, or getting some after-market springs w/o lift? I haven't looked in-depth, though I don't remember ever coming across after-market springs w/o lift. How bout add-a leaf? I know that will strengthen the springs, though won't it stiffen the ride and reduce articulation?

[CJ7Taz]

I knew a guy who’s wife’s cousin’s husband’s uncle …

Actually, I’ve never heard anything good about recurving springs. They have to heat and bend them, they will never be the same and will sag back worse than they were in a year or less. At least, that’s what the guy’s wife’s cousin’s husband’s uncle said.

Have you considered coil over helper springs. I don’t think the coils would hurt the ride as bad as an add-a-leaf.

[thorjeep]

Yeah, that is what I heard about re-curve as well. Have a link about coil over helper springs? Never heard of them.

[Jim_Lou]

About three years ago I dropped the left front in to a deep hole while going much faster than I should have been. The impact drove the axel back so severely that it put a 20 degree bend in the main leaves about 5" forward of the eye. I removed the spring pack and straightened it cold in a hydraulic press, and to this day can see no ill effects.

In light of that experience I'd suggest removing the springs and adding some curve yourself. You have nothing to lose except some time and skin off your knuckles.

[CJ7Taz]

Looks like I should have just called them helper springs. They just clamp on your shocks. I have no personal experience with them so I can’t make any comment about how well they do or don’t work.

If you do a search DO NOT include the words “coil over”, you’ll get a lot of links to full coil over suspensions and parts.

[TiminMb]

Springs are re-arched cold. They are actually a lot more maleable than you would think for spring steel. Once disassembled, a press between two blocks allows slow, repeatable changes to the spring arch. The bad news is that if you bent them once, you will probably do it again unless you do something to limit the stress put on them, such as adding an additional leaf. I knew a guy with a late model dirttrack car that used monoleaf suspension, and re-arching was a weekly event for him. As well, having asked at a local spring shop how they bend the eyes into the main leaf, I am told it is done cold bend. If you heated them, how would you properly re-temper them having once annealed the metal?

[xjy173]

Stock XJ rear leaf springs are "natural" (meaning from the factory) SOA.

IIRC, they are 51. 5 inches +- eye to eye. They might work better than the "natural" YJ SUA ones.

[thorjeep]

Jim,

I assume take the pack apart and have at them with a hydrolic press. Could you expand on the procedure? Thanks.

[TiminMb]

When you bend a spring through the range to which it can return to its original shape, that is elastic deformation. When you exceed that range and it takes on a bend, that is plastic deformation. For a given spring, the only thing you can do to prevent it going into plastic deformation is to limit the range of motion. Whoa you say, I want that massive articulation! Whether you limit it by making it stiffer, so that it moves through a shorter range for the application of a given force, or applying some other external limitation like a bump stop or helper spring, its all about the same thing. A longer leaf spring, on the other hand, can be compressed less and have the same travel at the wheel, as the bend is spread out over a longer spring. What I'm getting at is that you either limit travel, make the springs stiffer (add a leaf, helper spring, coilover, etc) or re-engineer the spring itself, such as a longer leaf spring.

[Jim_Lou]

Since the bend was over a fairly short distance I just put it scross the bed of the press with the kink up, and pressed it down a little past where it should have been when relaxed. Then I let the pressure off and determined about how much farther it had to go. I put it back in the press and took it back to where I had stopped, plus about 2/3 of the additional needed. It took several more repetitions until it was right back where it belonged. And I did it with the pack assembled, but that presented no problem because only two leaves were bent and there were no other leaves in the way at the bend.

To put an arch in the whole spring I'd suggest making a cardboard template of what you want the relaxed spring to look like. Then lay the spring across the bed of the press near the end of the spring and come down on it. It will take some experimentation to get the right amount of bend at that spot. When you figure out how much it takes, move the spring down a couple of inches and bend it that same amount again.

To get good results you'll need a way to get the same deformation in the press time after time. To do that I'd mount a dial indicator under the spring directly beneath the ram. With some experimentation you will be able to determine that pressing the spring to a certain point on the indicator will result in a certain increase in arch. Put chalk marks at regular intervals down the spring and you can make a nice, consistent change. I'd think every two inches should be good enough.

And Tim has an excellent point. If your spring has flattened out because it's being compressed too far, it won't be long until you're right back where you are now. In stock configuration the spring could only compress a couple of inches before running into the bump stop. There would be no need for the designers to make it capable of going any farther. Now that you're SOA in can go four or five inches farther. That may be getting it into plastic deformation. You may need to move the bump stops down some to prevent that.