moving your leaf srping underneath the frame rail!

[Stoney]

Everyone knows you are just as big a web wheeler as Jes, Paul Sinclair and :farmer: boy, so we should all take any advice you dispense with a big grain of salt.

CRASH

LOL!!!!!!!!!!!!!!!!!!

 

[Ed A. Stevens]

This would be the # 1 worst mod you could do to an XJ. There are a few simlpe things that make the XJ work so well in the rocks, the recessed spring hangers rank right at the top of that list.
Paul

I don't know if I would call lowering leaf spring hangers the #1 worst modification of an XJ, but for my current usage I drive my lowrider and slide the frame, rocker rails and rear corners off the rocks, rather than risk a full stop by adding more dropdown snag brackets. I'd have to think it through, for the wheeling I see, before adding to the rock catcher appendages.

I have a hard enough time snagging the little step lip on the bottom of the D44 pumpkin (time to exercise the grinder). The loose rocks in JV add to the challenge by changing the lines on all the obsticles (the guy in front of you will rearrange the trail). This constant change prevents a driver from simply following the established line, because the rocks move as they are driven over, and will catch anything they can snag. 33's are little doughnuts compared to the tires most of the regulars run, and the holes they leave swallow 33's with ease.

One thing I did notice in one of the modified photos was a slide rail angle cut on one of the forward spring brackets pictured. The angle cut would prevent a hard stop in the rocks (forward, but maybe not backwards, although the leaf should help there).

The other issue mentioned is the relative lowering of the roll axis compared to the CG for the rear suspension. Relocating these leaf hanger brackets is as close to a body lift you can achieve with an XJ. The roll axis elevation will not physically change, but the CG is raised (an extra leaf may be needed, or an anti-sway bar, to restore the resulting loss of roll stiffness).

The other result of lowering the front bracket hanger is less anti-squat for the same lift. This is something that could work for, or against, the performance balance of the front and rear working together on hillclimbs.

 

[ashmanjeepxj]

The other result of lowering the front bracket hanger is less anti-squat for the same lift. This is something that could work for, or against, the performance balance of the front and rear working together on hillclimbs.

The rear of the leafs will also lower the same amount as the front is lowered, so there is tille to no angle change on the leafs but since the center of gravity is increase the anti squat like you said will be smaller...


Anti squat= (force vector interseciton height)/ (Center of gravity)

Now caluculating the anti squat of a linked sytem I understand, but on a leaf spring how do you draw up the force vector intersection?

you need two vectors comming off the leafs and should have an intersection somewhere close to the center of gravity...

 

[Cresso]

I was considering moving the leaf springs under the frame for a long time and never once did I consider leaving the front spring mount underneath the frame to be a viable solution. I believe notching the frame, reinforcing the bujeezus out of it and mounting the front of the leaf spring essentially inside the frame rail to be the best method. This will also give you a flatter spring (closer to horizontal mounting position, not leaf arch), assuming you have the rear mount in the stock location. Flatter=more potential for flex.

 

[Ed A. Stevens]

Anti squat= (force vector interseciton height)/ (Center of gravity)

Now caluculating the anti squat of a linked sytem I understand, but on a leaf spring how do you draw up the force vector intersection?

With a leaf system you treat AS% analysis like a radius arm. The axle force vector is a line from the center of the axle (through the leaf pack radius arm clamped on the axle tube), to the pinned end at the chassis (the Instant Center). The intersection of the wheel contact patch IC force vector is also through the pinned leaf end on the chassis, to the front axle centerline, where the force vector intersection height is measured.

With a body lift, or relocation of the both leaf ends on an XJ, the IC height at the pinned end of the leaf arm does not change and neither does the wheel contact patch, so the force vector intersection height does not change. Only the CG height changes.

Use the same analysis model with a longer shackle and you can prove the AS% increases with the longer shackle (a taller front pin location, usually 1/2 the shackle length, and a taller CG).

Analyze what happens when the rear end jacks into full extension, with a highly angled leaf half radius arm, and the AS% goes way up under the dynamic load, sometimes to the point it dumps all the weight back onto the front axle -- and BAM, wheel hop.

 

[Matt]

One thing I did notice in one of the modified photos was a slide rail angle cut on one of the forward spring brackets pictured. The angle cut would prevent a hard stop in the rocks (forward, but maybe not backwards, although the leaf should help there).

The other result of lowering the front bracket hanger is less anti-squat for the same lift. This is something that could work for, or against, the performance balance of the front and rear working together on hillclimbs.

Thank you Ed! As always what I was trying to explain you lay out very simply. The only time I have had "problems" hitting those brackets is on a few of the big downed logs we have around here - and it is a really minor problem usually when one rear tire come up causing the other side to be loaded and decreasing the ground clearence - just back up a little and give it a good blip of the throttle to get some momentum - once the tire gets up to the log you go on up - I have yet to get actually hung up on them in the last 2 years even while running 33's

I lowered the front eye of the spring just a hair as the junkyard CJ lift shackle I used for the back was not quite tall enough and I did not want to get into frenching the frame

For those wondering what type of terrain I run here are two examples: A. plenty of sloppy stuff (log with fill in front) B. also some nice rocks and big hills C. (not shown) all of the above with 24 - 96" of snow on it

It works for me and thats what keeps me happy...

A.

B.

Matt