"I have the ACOS in the front and rear myself. I just recently got the rear but I have had the fronts on since April of '07. I decided to get the fronts after I installed the front bumper and lost about .5" of height. Having heard about the height losses that several other people have experienced after they have added bumpers, winches and the sort, I figured they would be better than a fixed spacer since my build was going in stages.
Throughout the time that i have had the front ACOS, I have adjusted the spacer portion 4 times. These adjustments varied from recovering lost height from the bumper and again after the winch, to adding additional height/clearance to alleviate rubbing or just plain adding height. Having had this kind of flexibility with the front I had to get a set for the rear. Especially considering that during my build process I have accumulated a set of .5", 1", and 2.5" TeraFlex spacers for the rear. Speaking of which, anyone interested in any of those spacers?
The installation of the fronts are pretty involved. Here is a link to the write-up I did back when I installed them: Front Bumper & ACOS Pros Installed. You must cut off the factory bumpstop and weld these in. It is noted in the instructions that the installation of the front ACOS is irreversable. The rears aren't so bad. Remove the spacer/factory isolator from the top of your spring, mark and drill some holes and then install.
I do have to say that I did splurge when I got the fronts and got them with the gas charged bumpshock and I am very happy with them. The rears I am currently only using them as an adjustable spacer but plan to add the gas charged bumpshock at a later date.
I would consider these to be one of best and most utilized mods that I have done to date. And, knowing that I still have 2" of height that I can add at will is a good feeling. The only thing that would make these cooler would be if they were motorized and remotely adjustable from inside the cab. Long story short, I am very happy with them and would recommend them to anyone in a similar situation."
Tom Carlsen, Customer
JK Owners forum