I haven't posted in years, but I just did this upgrade myself. I've used the Eibach springs with the KYB shocks. A little background, I have a 2007 V6 and have always hated the suspension as being too soft. I prefer a suspension that was much firmer for driving the mountain roads around here (anyone heard of the Dragon?) so my whole interest was improving steering, braking, and getting rid of that floating feeling I find with the stock Sonata suspension. I could care less about looks and the drop look.
Doing the rear, the hardest part was getting the old shocks off, specifically the lower shock bushing. I ended up using a Dremmel to cut the shocks and expose the bushings. After getting all the rubber off the bushings I used a torch to heat the remaining steel sleeve and free it up. It took about an hour work per bushing but I finally got them off with much brute force and ignorance. I did also use the Dremmel to make a couple of relief cuts in that final sleeve which I believed helped. There was some rust powder under the bushing once they finally came off, but nothing bad. I did a lit sanding of the stud and put some penetrating oil on it, the new shocks slipped right on like a dream. No spring compressors needed for the back springs.
On the front, the bugger was getting the old strut tower out. A few years ago I considered doing this project and was told to compress the springs before removing, well I couldn't find a way to make that work, but if you take your time and use a floor jack, then getting them out without the spring compressor is totally easy. Once you get the struts out use spring compressors and an impact wrench for best results. To get the old springs off takes a lot of compressing, and that was the worst part of the fronts (getting those compressors on and off). Once you get the top off the struts (compress a lot before trying to take it off!), putting the hardware onto the new strut and spring system is easy. You will have to use the spring compressors a little to get the hardware to bolt on, but not anywhere nearly as much as you did to get the old ones off. It all bolted right back in easy as pie.
I'll add that while I had it apart I went ahead and put Weaver gold ceramic brake pads on all four wheels.
Now I didn't do before and after measurements to check the drop because I really don't care, but it is lower for sure. I had to readjust mirrors on the first drive to compensate. I immediately noticed the change in handling. The Sonata tracks just where I point it, I don't have to compensate for the body roll anymore. I also don't notice the annoying roll when making hard turns like I use to. Braking is much better and smoother, some of that may be due to the Weaver ceramic gold pads, but I also notice the car sits a lot flatter during hard breaking instead of pitching up like it used to. So far I am happy (I just finished this yesterday), but I do notice I need an alignment now. I called my shop and he told me lowered Sonatas will not get a proper alignment. Apparently there is no camber adjustment on a Sonata only toe alignment. So that can be done, but not camber. Now I'm looking into replacing the ball joints with something that can be adjusted. Looks like the consensus is the Eibach approved solution does not actually fit the Sonata (WTF?) and there is a good chance that this one will work for an Eibach spring upgrade, but probably not an HR which is a lower drop: MEVOTECH Part # MK7452 RockAuto Parts Catalog
I can probably change these out myself before taking it over to the alignment shop. Saves on the cost if I do labor myself and it also gives me a better knowledge of how all this stuff works together.
Anyhow, I thought I would share that, and if anyone has any advice, comments, feedback etc. it would be greatly appreciated.