Spring Installation guide for Subaru WRX STi:
1.) Remove the rear seat.
Tools: 12mm socket. Socket extension helps.
There are two brackets at the front of the rear seat. Remove the bolts holding them in and pull out the lower seat cushion. There are three brackets holding the seat back in. Once the bolts are out you can lift the cushion off. There are brackets at the top that support the seat; make sure those clip in properly when you put it back in. Also pay attention to how the cushion fits through the seat belt.
2.) It is easiest to bust loose the 17mm strut top nuts while the car is on the ground. So that’s what we are doing here…
Once the seat is out you can get to the rear strut dust covers. You’ll want a couple of tools to get to these nuts since the access is pretty tight. A 12mm open gear wrench (pictured) is nice. Also, standard 12mm sockets in various depths will be helpful. Unless you have air tools that can fit on these, there is a lot of wrenching involved since you can only get a few degrees per turn on some of them. Strut cover removed. Note the “out” inscription, and make sure it faces “out” when you put it back on. Top of the strut showing the nut that needs to be loosened. You should be able to get on there with a 17mm deep socket and loosen it a few turns. Just bust it loose, do not remove it at this point!
This next part isn’t critical now, but you will need the info later.
In order to make sure the strut isn’t spinning in the shaft, you need to insert a 6mm hex/allen wrench
into the strut top, and hold that still while you turn the 17mm nut. This is the contraption I use.
Now to the front.
Remove the little rubber dust covers in the center of the top mounts. Again, bust the top nut loose. On the front passenger side there may be a bracket that holds an alarm chirper. It doesn’t really matter if you take the 12mm nuts off now or later, I am just including it at this point in the process. If you do loosen them now, again, make sure to keep them on at least a little bit so the struts don’t fall off later.