I thought I would post a picture and information to help people gauge the proper length of shackles to use to obtain the desired lift for the rear of their S10 Blazer. Please note I have taken into account the change in weight distribution from the front of the vehicle to the rear as you lift the front or rear of the truck.

The image below shows you that you do NOT obtain the same about of lift as the length of shackle you install.

The front pivot point of the rear leaf spring remains stationary. Because the position of the rear axle is closer to the pivot point than the shackle, this cause less lift than the specific size of shackle can produce.

See lables A1, A2 and B1,B2 in the image below. Notice the distance between points B1 and B2 are greater than the distance between points A1 and A2.

So, here is a chart I created to help you get the intended lift with the proper shackle.

Shackle Size Actual Lift Obtained
1 1/2" 5/8"
2" 7/8"
2 1/2" 1"
3" 1 1/4"




I hope this helps you choose the proper shackle set for your truck. Please feel free to post helpful information.

 

In your chart...are you suggesting someone actually use a 3' shackle? Or do you mean 3' longer than stock...

One thing though: The stock shackle angle is pretty close to 90*....and when you install the lift shackle, it gets installed at a lower angle which accounts for the axle dropping farther away from the body. This is why on S-series trucks, you get half the height in lift of the amount longer the new shackle is over stock...so a 3' longer shackle nets you 1.5' of lift...the pic chops an extra 1/4' off to account for what would be pivot....the shackle absorbs the shortened leaf, which leaves the axle in pretty much the same place. And...I'm pretty sure on blazers the axle sits in the center of the leaf...not 22' from the hanger.

 

I took actual measurements of my rear leaf and the axle position. The spring is 52" and the axle center is mounted at 22".

I then laid out a straight edge on my work bench, measured out 52" and marked off 22". I lifted the 52" point at each of my pretend shackle heights and measured the height of the 22" point to get my final actual lift height.

My picture should be fairly close and accurate without actually placing all those shackle heights on my truck.

And no, I`m not suggesting any particular height of shackle.

EDIT: Please don`t let the inaccuracy of my drawn lines and angles throw you off. I`m no draftsman, but my theory should be very close and my measurements accurate.

 

Correct me if im wrong, but arnt the shackles bigger than the accual size they say they are? Like for example a 2inch shackle is bigger than 2 inches. I thought thats for the extra needed lendth to fully lift it the 2inches.