How do lowering shackles work?

[siggyfreud]

Might be a dumb question, but how do lowering shackles work? It's been awhile since I had my leafs together it's hard to envision how they operate. Do they just let one side of the leaf swing up higher? When ordering them, so I just need one pair, or a pair for the front and back?

When I took my rear apart everything was so rusted together I plasma'd a lot of the shackles and parts to get it apart, and now I'm trying to figure out what I need to get it all back together.

[Captainfab]

You only need one pair since there are only shackles at the rear of the springs. The longer shackles when mounted in tension will lower the body of the truck by aprox 1/2 of the increased length of the shackle. IE: a 2" longer shackle will lower the rear aprox 1".

[markeb01]

Typically leaf springs are mounted on a solid pivot on one end, the other end has a shackle mount. The purpose of the shackle is to allow the spring to grow or shrink in length when encountering bumps or holes in the road surface. If both ends were mounted solid, a leaf spring could not move up and down.

Lowering or raising shackles use the same principle, depending on whether the eye of the spring is mounted above or below the other end of the shackle. If the spring eye is below the bracket (like early Camaros, etc) installing long shackles will jack the rear end way up in the air. This was very popular back in the 70's to fit tires on the rear that were too big for the car.

If the spring eye is above the bracket, adding long shackles will drop the rear end of the vehicle (by raising the end of the spring up closer to the chassis). The problem with long lowering or raising shackles (in addition to clearance issues), is they often adversely affect handling because the rear end is allowed to sway back and forth on the shackle plates, effectively steering the vehicle undesirably.

[siggyfreud]

Great info, thanks guys!

So Mark, based on what you said would it be advisable to do drop leafs as opposed to longer shackles in regards to keeping the handling solid? Leafs are about 6-7x the price as shackles, but if it's the right way to do it then . . .

[markeb01]

Depending on how you use the truck, you might get the same result by just removing a couple of leaves. I did that on my 46 Ford front spring to arrive at the ride height I wanted.

And you don't necessarily need to get new springs either. Older spring shops can re-arch (or flatten) your existing springs for a lot less than the cost of new ones. It's been many years since I needed those services, but it was easy and cheap compared to new springs.

Personally I'm not a fan of long shackles for the reasons noted earlier.

[Captainfab]

Keep in mind that removing leafs to lower the ride height will result in a softer spring that will be more susceptible to spring wrap.

[fleetsidelarry]

siggy, have you thought about blocks, i.e. lowering blocks? a 2" block will give you a 2" drop. you can even use a combination of blocks and longer shackles. and an anti-sway bar will help with handling

[siggyfreud]

Thought about it, but I've also read it can lead to bad wrap/hop. It sounds like the best way is going to be lowering springs. I'll probably load it up with the old springs, see how I like the overall height, and then adjust accordingly.

[SCOTI]

Originally Posted by fleetsidelarry

siggy, have you thought about blocks, i.e. lowering blocks? a 2" block will give you a 2" drop. you can even use a combination of blocks and longer shackles. and an anti-sway bar will help with handling

Blocks only work if the rear end is flipped vs OE truck position (housing under the leafs). How much drop is desired here?

[fleetsidelarry]

I was thinking the housing was above the spring on these older trucks.