This not exactly correct...
Installing an AAL correctly will lift the vehicle.
One it increases the spring rate meaning the entire pack will compress less with the same amount of weight (sort of what you said in an earlier post, but the end result is some lift). If your spring are old/weak, then yes your just getting the orig height back, but it is still lifting. If you have good springs already it will lift it by using the increased spring rate.
Also.. the AAL is NOT installed at the bottom of the pack. If you do that the AAL will by trying to lift/change the spring rate of just the overload spring which normally isn't affecting the main left until the main leaf comes down to meet the overload. It goes right above the overload spring which is the bottom of the pack.
If your SOA it changes quite a bit.. the AAL increases height by increasing the height of the entire spring pack AND it also increases the height for the same reasons it increases the height in a SUA.
If you like your ride, keep the current springs and use shackles to lift the back end a little.
As for the orig question/issue.. to get 4" you won't get that with AAL without turning your rear suspension into a brick.. Even with adding shackles..
Get new springs.. There are people that have tried to get a SOA down to 4" of lift by using shorter shackles and stock springs and they still ended up with 5" or so lift..
~Mark
mark i do not know what vehicles you have been working on but if you install anything between the spring and axle in a SUA setup whether it be block or add a leaf you will be lowering the vehicle and even putting the add a leaf between the overload and the main spring pack will only remove the spring sag and not all leaf sprung vehicles have the overload spring
i have lowered countless numbers of nissan pickups using this method, nearly all nissan 2 wheel drive pickups have a SUA setup, and all of their 4 wheel drive pickups are SOA configuration
also all of ford full size 4x4 trucks are SOA and a good majority of Fords mid size vehicles are SUA as well as SOA including the explorer and the 2wd bronco2 and some 2wd rangers i have a 2wd ranger that has a Factory SOA setup and my f250 4x4 has a Factory SOA setup so i know the difference
If you are using an add a leaf to correct spring sag YOU ARE NOT LIFTING THE VEHICLE YOU ARE RESTORING RIDE HEIGHT, and yes in order to acheive this the add a leaf must be placed at the bottom of the spring pack(just above the overload if equipped) so that it uses the curvature of the add a leaf to correct the sagging spring
if you place it on top of the spring pack all you will get is a spring pack that is a little taller at the center with the ends of the add a leaf hanging in the breeze serving no function whatsoever
this is an example of a spring over axle configuration
yes it is a jeep but a good representation of what i am talking about, if you add blocks or add a leafs to this vehicle or any other with this configuration it will get lift no matter what
here is a spring under axle configuration this one is the front suspension of a suzuki samurai with no blocks as you can se in the photo if you add blocks or an add a leaf between the axle and spring you will actually lower the ride height of this vehicle and any other vehicle with this configuration the only way to get lift using this setup is to use taller shackles or place the add a leaf under the spring pack opposite the axle, or use taller springs
by the way in case any of you are wondering i used to work very closely with a 4x4 mod shop in Mohave Valley,AZ