Front Shackle Question/Theory

[Gambler68]

So I'm out there staring at my front, thinking about lifts and all that jazz...

Running BJs lift shackles in the front (well, I have them anyways)..does the rear *have* to be a fixed point? Could one run the stock shackles at the rear of the front spring? They fit. It would drop the rear of the spring down about 2" if done so..now, of course, instead of your springs moving in an arc, they would *want* to move like a swing, torwards the rear (like having a shackle-rear setup) only more so. Could that be 'fixed' with a simple trackbar setup? According to the handy lil mini-book from Four Wheeler mag I have laying around, extending shackle height on behind the axle shackles leads to more caster. Only problem I can see is that they probally wouldn't last too long, being just stamped steel. But I heard chevy ones are thicker. Just thinking, wondering if it's possible. I'm not going to do this of course

Should I stop thinking? hahahha. don't answer that. Explain why this can't work. If anything, for the exercise in suspension theory.

[adamsclarke]

If I am reading you correctly..what you are talking about is a shackle reversal (not flip) This makes the stationary point at the front of the frame and the shackle in the rear. It's a debate that has been beat to death for many years. Pros...It allows the axle to move in a more natural direction when hitting bumps...moves the axle forward a bit..etc... The cons are....more travel..so you'll need a longer slip on the driveshaft and the axle will tend to want to walk forward when climbing large obstacles...like rocks.

It's smoother on road...but will give you more brake dive.
I am considering this when i do my SAO soon. I probably will not use the factory hanger...but box th eframe and then sleeve the frame for the shackle bushing.

[aerocorey]

I don't think he's talking about a shackle reversal, I think he's talking about running shackles at the front and rear of each spring at the same time to allow the spring fo "float" under the frame. That would scare the he** outta me. I could almost see the springs loading up and being able to unload dangerously at steep angles (anyone running revolver shackles?) with potentially poopie results. I'd also think putting a trac bar in would result in alot of torn up trac bar bushings.

Sounds like a cool idea that I'd never try!

[Gambler68]

I don't think he's talking about a shackle reversal, I think he's talking about running shackles at the front and rear of each spring at the same time to allow the spring fo "float" under the frame. That would scare the he** outta me. I could almost see the springs loading up and being able to unload dangerously at steep angles (anyone running revolver shackles?) with potentially poopie results. I'd also think putting a trac bar in would result in alot of torn up trac bar bushings.

Sounds like a cool idea that I'd never try!

yeah, pretty much might be neat to try on a budget offroad only rig.

[goldhammer]

Hat now sitting on 6 inches of straight hair and off top of head. Unless you figure a way to anchor the spring end of the shackle or one hell of a stout radius arm type deal, I would not even get in it. If one side moves to the rear and the other gets "pulled " to the front, you go straight sideways. Would be h@ell on the front slip yoke as well.

Neat thought but toss it in file 13 for now me thinks.

[Gambler68]

Hat now sitting on 6 inches of straight hair and off top of head. Unless you figure a way to anchor the spring end of the shackle or one hell of a stout radius arm type deal, I would not even get in it. If one side moves to the rear and the other gets "pulled " to the front, you go straight sideways. Would be h@ell on the front slip yoke as well.

Neat thought but toss it in file 13 for now me thinks.

If ya had hair like mine, it'd be 3 feet in the air

Okay, twas a silly thought. I've wondered though, I've never seen a shackle behind the axle on an FSJ, though from looking at Four Wheel Offroad it's been done on other front shackle rigs. why?

[scantar]

So I'm out there staring at my front, thinking about lifts and all that jazz...

Running BJs lift shackles in the front (well, I have them anyways)..does the rear *have* to be a fixed point? Could one run the stock shackles at the rear of the front spring? They fit. It would drop the rear of the spring down about 2" if done so..now, of course, instead of your springs moving in an arc, they would *want* to move like a swing, torwards the rear (like having a shackle-rear setup) only more so. Could that be 'fixed' with a simple trackbar setup? According to the handy lil mini-book from Four Wheeler mag I have laying around, extending shackle height on behind the axle shackles leads to more caster. Only problem I can see is that they probally wouldn't last too long, being just stamped steel. But I heard chevy ones are thicker. Just thinking, wondering if it's possible. I'm not going to do this of course

Should I stop thinking? hahahha. don't answer that. Explain why this can't work. If anything, for the exercise in suspension theory.

All this snow's making me think crazy things too.

Colorado's just not supposed to be like this.

[shimniok]

There has to be a fixed point because the spring not only suspends the vehicle and articulates over / absorbs bumps, but also LOCATES the axle front to rear and side to side.

The front mounted shackle is found on Jeeps all the way back to the original, I believe. I don't know if this was intentional but it wouldn't surprise me --- as your springs compress, with the front shackle the axle (and tire) moves FORWARD, potentially INTO that rock you are trying to climb. That is desirable because the more force applying a tire to a surface, the more grip it can offer. So front shackles should help you climb over rocks and ledges better vs. rear mounted shackles. However, supposedly the ride is better with rear mounted shackles.

Michael

[adamsclarke]

I got ya...so yeah..I have seen it done, but with 2 rear trailing links to keep the axle wrap at a minimum and a panhard for side to sid....but why anyone would go to all that trouble and suspension deisign and use leafs insead of coils/coilovers/ellipticals is beyond me.
I believe the YJ in UA 2004 had it in the rear as well.

[aerocorey]

I've never seen a shackle behind the axle on an FSJ, though from looking at Four Wheel Offroad it's been done on other front shackle rigs. why?

I can't speak for the technical reason why, but for me it's sort of a matter of driveline angle. Maybe I'm being too paranoid about my driveline angle, but moving the shackle to the rear of the spring without installing some sort of a wedge between the axle and spring would pretty efficiently increase your driveline angle with no noteworthy advantage. Not only that, but if you're SUA any wedge you might install to correct your driveline angle will lower your Jeep a bit.

As I said, not technical, just this guy scratching himself looking at a Jeep. I call it a matter of pros and cons. I guess the guys that have done a shackle reversal weighed it and came up with more pros.

[Gambler68]

... However, supposedly the ride is better with rear mounted shackles.

Michael

gotcha, yeah, the rear shackles are better for ride/washboard stuff from what I've read.

[Gambler68]

All this snow's making me think crazy things too.

Colorado's just not supposed to be like this.

no sheet! I'm going stir crazy. If only I had moved faster and gotten my J10 in the half finished garage before all this white crap fell and oddly won't MELT. gah.

[Herk]

Shackle reversals (front to rear) have been around for years. This setup was OEM on 2 1/2 ton military trucks, but most light trucks put the shackle at the front. Yes, the theory is that the axle will move with the bump and not into it with a rear mounted shackle. This is said to give a smoother ride. Also the spring is "in trail" so you should have less wander by putting the articulation at the rear. Another main reason why the CJ and FJ40 guys have done this is because you can gain about 3" of lift and still use the factory spring.

Reality check time! First, using a 4" lift FSJ spring as an example (which will have about 4" of camber, and about a 300# rate, and a total travel of 6" to the bump stop), lets look at what happens when we hit a bump. Start off with a little bump driving off a curb say at 15 mph. The springs compress about 2", and as they conpress they get longer by say 1.5". You axle just went forward 3/4". This kind of a bump will flip a longneck out of the cupholder, so ride quality is pretty much out the window. That 2" of compression took 1200# of force. On the highway, you are generally looking at wheel movements of about 1/2" - 1" so axle movement is insignificant. On the trail on really uneven ground or over rocks, speed is slow enough that it really doesnt matter. And on the street, you lose all of the "anti-dive" built in if you reverse the shackle.

As for the wander, a fresh set of bushings, CORRECT caster, and a low angle on the drag link will do far more.

If you were to put shackles at each end of the spring you would create a paralellogram and the whole mess would just slip forward or aft until the spring eyes hit the frame at one end. At this point the axle would have moved 2or 3 inches and with one eye against the frame you would be back to having one end locked in position and the other free, but now with the free shackle angle all messed up. You would need to use a 4-link to locate the axle fore and aft. Coil spring suspensions must have this kind of location, so look under the front of a TJ, Grand Cherokee, or Dodge truck for inspiriation. Just replace the coil with a double shackled leaf any you would easily have the heaviest most colplex suspension on the trail.

Long story short, there are better ways to spend you time and money.

[fulsizjeep]

Ryan... The SOA on Luna Wag has the shackles on the rear instead of front. It flexes mucho grande. I do not understand the geometry, but you are welcome to look it over next time over the mountain this way.