HD front shackle

[Mastiff]

Can you explain what happens to the extra half inch of lengh on the shackle? Does the front end sit slightly higher, or does the shackle tilt back a little more than stock? A combination of the two? I'm just asking because I can't really picture the physics of it to predict how it works. /forums/images/graemlins/tongue.gif

The web page mentions that it affect caster angle and may influence the amount of highway wander. It tilts the pinion down then? Funny thing is, I have a shim in there to tilt it up. But I do wander some on the highway.

 

[heavy4x4]

Now this is an exaggeration, but for the sake of explaining, think about putting a shackle 1 foot longer than stock back there. What would happen would be that the rearmost part of the spring would be pushed downward, the pinion would be pointed downward more (caster increasing), and you would gain roughly 6" of lift. This six inches is the result of only moving one half of the front spring down 12 inches. *Disclaimer; do NOT put a shackle more than about 1-2" longer than stock in!*

Anyway, that's basically the physics of it. With only 1/2" difference, it's not going to change caster too much and the shackle will still be relatively straight up and down. The reason for the little bit of extra length is to keep the spring eye from hitting the frame when the leaf spring flattens while stuffing a tire.

 

[Mastiff]

Thanks, that makes sense. /forums/images/graemlins/thinking.gif

 

[Z3PR]

But do you gain 1/2 a inch of lift ??? I was under the impression you do.

 

[84k5]

You only gain half of the increase in shackle length. So in this case you get 1/4" of lift.

 

[bigjbear]

If it's 1/2" longer you gain 1/4" of lift. You are only moving the mount point of one end of the spring.