Shackles

[steph74]

I know it is all over the forums and the internet and most likely this one too..

Well, I would like to open a discussion on shackles and have expert opinion of our members / readers...

What do they do, what is the advantage of Shackle lift if any, Revolver, long, short... anything shackle related will be good to hear.

Including bushings, trick to install, removal, repair etc...

[4.3LXJ]

There are a couple of things. First is that the rear spring on an XJ is designed to have the rear of the spring higher than the front, and so is longer in the back to even out the forces on the whole spring. When adding a shackle, you put more force on the rear of the spring than it was designed for. This will cause a stock rear spring to eventually sag, just like the old muscle cars of the 60s did with extended shackles.

Secondly, for every inch of shackle extension, you change the pinion angle by 1° which can cause a driveline vibration. So lets say you raise the rear 2". That is a 4" extension which will cause a 4° change in pinion angle and require the addition of a shim to correct that.

[steph74]

So what I don;t get is for what purpose the engineers put a shackle in the first place.
Does it provide a better suspension ?

[4.3LXJ]

Steph

Take yourself back to some basic geometry. The springs are arched into a semicircle. If you flatten the spring, it is at its longest between the two bolts that hold it in. As you bend it, that distance shortens until ultimately it would be zero when the ends touch. It never gets that far, so in reality you have a couple of inches of change in distance between the two bolts. The shackle pivots to take up the change in that distance.

[steph74]

Steph

Take yourself back to some basic geometry. The springs are arched into a semicircle. If you flatten the spring, it is at its longest between the two bolts that hold it in. As you bend it, that distance shortens until ultimately it would be zero when the ends touch. It never gets that far, so in reality you have a couple of inches of change in distance between the two bolts. The shackle pivots to take up the change in that distance.

Ah yeah sometimes I really need to stop and think.... but sometimes I think that stupid questions help everybody too ;)

I did have to use a piece of paper to visualize it though ;) makes sense

[Mudderoy]

Ah yeah sometimes I really need to stop and think.... but sometimes I think that stupid questions help everybody too ;)

I did have to use a piece of paper to visualize it though ;) makes sense

I didn't know why.

[jccatt]

So does a shackle relocation kit work different on the angle?

[LizardRunner]

If you want to use extended shackles, you need to do both ends of the spring, that keeps the geometry correct allowing lift and not inducing sag or breaking. The purpose of boomerang rear shackles is to help keep the geomerty closer to correct, But, if you leave the front of the spring in the stock mount, you still have induced a sag situation, just not quite as bad a one as straight shackles. A shackle relocation kit, unless it adresses both mounting points, is still a point of sag/breakage inducement. a better method would be to add leaves or re-arch.

Rubber bushings are softer than any of the different Poly bushings so they give a softer ride feel. Red poly is softer than the Blue, the right place, in my mind, for poly bushings is in the anti-sway bar mounts, shock mounts. Engine, transmission mounts are subject to lots of vibrations, so the rubber bushings would be better for a smoother ride.
Just my 2 cents

[jeepxj95]

great discussion. answerd a few ?'s

[jccatt]

Ok, so how do you extend the front of the spring?

[steph74]

this is why i like this forum ;) you got questions, you get "educated" answers....
isn;t it great to be able to have a discussion without the usual "Revolver Shackle rock because this is what I use and I have always been happy with it"

[Mudderoy]

This is interesting in as much as the Rough Country 4.5" leaf pack and the 6.5" leaf pack are the same. For the 6.5" lift in the rear they add a 2" shackle.

[LizardRunner]

Ok, so how do you extend the front of the spring?

That's where you do some bracket fabrication work. It's much simpler to have the springs re-arched or set up a new main leaf. I'm talking with the guys at our local superior spring shop about the best way to get the rear lifted to match the front springs so you sit level.

[4.3LXJ]

So does a shackle relocation kit work different on the angle?

Yes, the relocation kit does move the top mount of the shackle forward, making an increased angle. It also acts as an extended shackle because the mounting point is moved down also.

But there is a drawback that is never discussed. The change in angle also puts more force on the shackle bushing and it will wear faster.

I can't readily prove it, but the mechanism of the increased angle and different forces on the one end of the main leaf causes the main to actually unflex into more arch on the one end while the rest of the spring functions normally. My opinion is that this is what is responsible for the reported improved ride.

[4.3LXJ]

This is interesting in as much as the Rough Country 4.5" leaf pack and the 6.5" leaf pack are the same. For the 6.5" lift in the rear they add a 2" shackle.

This is done for two reasons. One is production costs. The other is that it is hard to get enough arch in a spring at that height and allow it to flex that much without destroying the temper of the spring, especially since the more modern production methods have come into play. So to compensate for that, they just give you an extended shackle and probably an extended bump stop for that height.

[jccatt]

So I am better off adding a leaf than an extended shackle.

[4.3LXJ]

So I am better off adding a leaf than an extended shackle.

That is correct. Preferably a full length leaf.