Rear leaf spring shackle question? Please help!

[GMC"ER]

Ok here is my question and I know it is a kinda stupid one at that. I just bought a set of 2" drop shackles for my rear leaf spring 69 GMC. It has two settings on top and one set of holes for mounting the leaf into on bottom. My question is which set of holes on the top is for the lowest stance setting top or bottom set of holes? I have tried both with not a lot of difference? I would think it would be the top most set of holes for the lowest ride right? Thanks for a confused 69 owner, Robert

[Mike C]

The top set of holes gives the lowest stance. But because of how shackles work, if the top hole is 1" away from the bottom hole, it only adds 1/2" of drop. (And conversely on a compression shackle like a Camaro or a Jeep, a 1/2" of lift). So therer isn't a whole lot of difference between the two holes.

[GCncsuHD]

^Exactly what he said. For each inch in difference of "effective" length of the shackle, you will get 1/2 that amount in lift/lower. So for the 2" drop, the shackle is 4" longer than the stock shackle. Use the top set of holes for the most drop, usually the different holes are used to correct a little lean from side to side.

Also make sure you are only tightening the bolts on the shackles after you have the trucks weight on the ground (or jack the axle up to mimic the trucks weight on the ground if you need to leave it on jackstands to get under it). Too many times have I seen/heard people complain they didn't get the full amount of drop or a rough ride after they tightened the shackles down with the suspension drooped, which effectively preloads the suspension at that height.

[Bryan H]

I had to notch my bed crossmember to get tthe shackles to work in the top holes because the leaf springs hit the crossmember. My is a fleetside so keep that in mind when you are putting them on. I also replaced the springs with a 4" dropped leaf spring.

[GMC"ER]

Thanks guys! A lot of good information, Robert