I finished this tutorial at about 3am local time and no one is awake to proof-read it. If you find errors, please PM them to me.
Also, I posted this hear to keep it with its companion tutorial on the trailing link swap. If a mod feels they're better placed in the DIY forum, please move them.
I'm writing this tutorial for kind of a strange reason: The install is very, very easy. Frankly, if you can rotate your tires, you can swap your rear of lateral link bushings. The problem is that no one seems to know it. The trailing link and its bushings are an often overlooked part of the suspension. This is especially criminal when you consider how amazingly easy it is to swap both the bushings and the links in comparison to how much the swap helps address one of the biggest problems with daily driving an Impreza (driveline bounce, especially a problem for the DBW cars). This tutorial covers just swapping the rear of trailing link bushings using the Big Sky Bushing Tool (talk to BigSkyWRX to get the tool) as though it were the only thing being done. There's also a companion tutorial to this one describing how to swap the trailing links themselves. If you're doing one, you probably want to combine both installs into one meta-install because they share many of the same steps. When reading these instructions, keep in mind that these steps will only teach you how to swap the bushings using the Big Sky Bushing Tool.
By the way, clicking on any of the images will get you a larger, more detailed, image.
Start the install by jacking up the car and removing the rear wheels. The front wheels can stay on. They can stay on the ground, for that matter. Once you have the wheels off, crawl under the car from the back and look towards where the wheels normally are. You should see something that looks like this:
The lump hanging off the bottom of the knuckle is the rear of trailing link bushing. The trailing link extends from that bushing on the rear forwards to where it bolts to the chassis. We'll be removing the rear bolt to swap the bushings.
OK, now that you know what you're working with, get out from under the car and look into the wheel well just in front of the brake rotor. You'll see two lines bolted to the trailing link. They'll look like this:
We need to detach both of these lines from the trailing link before removing the link. While it's not strictly necessary to do this, you'll have a REALLY bad day if you manage to cut the ABS sensor line during this process. There are two parts to the bracket. If you look at the previous picture, there's a hoop that sticks up on top of the link and a bolt farther up the link. Use a 12mm socket to remove the bolt on top of the link and then crawl back under the car to remove the bolt holding the hoop. Do this on both sides of the car. Since you can't see the second bolt from beside the car, here's a view from underneath, showing the bolt (note that your bracket might look slightly different depending on model year):
Next up is detaching the rear end of the railing link itself. Strangely, the nut is on the outside of the trailing link between the knuckle and the brake rotor. This makes it slightly tricky to find and to loosen. This picture is taken from the rear, showing you the bolt you'll be working on and how it hides behind the rotor:
The best way to remove the nut from this bolt is to use a pair of 6-point combination or box wrenches (NOTE: DO NOT TRY TO USE 12 POINT WRENCHES. If the nut is corroded in place, 12 point wrenches will very likely round off the nut) and a heavy (2.5lbs or greater) plastic dead-blow hammer. A socket and a breaker bar could be used on the head side, but would not fit on the nut side. Place one wrench on the head (inside of the bolt to prevent it from spinning. Place the other wrench on the nut (outside) in a position that allows it to be easily struck with the hammer. Strike the end of the wrench VERY HARD with the dead-blow hammer. This is not a time to be gentle and worry about breaking something. You need to be in full-on "Lothar SMASH!"-mode here. Keep beating on the wrench until you can spin the wrench by hand. After that, use a ratcheting wrench on the head side while holding the nut still to remove the nut. Now remove the bolt from the link. CAUTION: Depending on manufacturing tolerances, this bolt may be under considerable strain. It is possible that the link will spring away from the knuckle and/or that the knuckle will spring away from the link (taking the lateral links and strut with it) when you remove this bolt. Don't have you head in the way!
At this point, you get to experience the wonder that is the Big Sky Bushing Tool. This specially designed tool is a miracle of cleverness. The first thing we need to do with the tool is get it ready to use. Hopefully, the person using the tool before you would have been kind and cleaned it before returning it. However, some people suck. Make sure the tool is clean inside and out and that there's no grit or metal shavings in the threads of the rod. After cleaning the tool, lightly lube the threaded rod with silicone grease.
To get the existing bushings out of the knuckle, the tool must be configured into Removal Mode. I'm going to give both a verbal description of how to do it, and provide 3 pictures of it (an overview and 2 close-ups). You may want to print out the full-sized version of at least the Overview of both Removal and Installation so you can look at them while you're under the car.
Overview of Removal Mode:
First, spin one nut about 3" down the shorter piece of threaded rod. Now slide a ratcheting pass-through wrench (such as a Gear Wrench Vortex wrenches) down over the rod and onto the nut you just spun down the rod. Spin another nut about 1/2" down the rod, effectively trapping the wrench on the rod. Slip a washer down the rod to sit on the nut you just added. Add a 3rd nut to the end of the rod, sandwiching the washer between 2 nuts. TIGHTEN THE HECK OUT OF THE TWO NUTS SANDWICHING THE WASHER. Basically, you're trying to lock the two nuts against each other with the washer in the middle so neither nut can spin.
Now flip the rod over so you can add things to the other end. Place the Bearing Spacer on the rod and let it slide all the way down to the nut and wrench. Place the End Cap Bearing washer onto the rod with the smaller flat side facing the Bearing Spacer. Slide the Bearing Washer down onto the Bearing Spacer. Place the End Cap onto the rod with the flat side facing the Bearing Washer and slide it down. Finally, place the large Tapered Tube with the smaller end facing the End Cap onto the rod. The assembled Tool should look like Detail 1 at this point. You're ready to go to the car!
Crawl under the car and locate the hole through the center of the existing bushing. Slide the end of the threaded rod through the bushing so that the large, open end of the Tapered Tube comes to rest against the knuckle. Place the Plunger onto the end of the threaded rod where it comes out the other side of the bushing making sure that the indented side of the Plunger faces the bushing. Thread a nut onto the rod on the other side of the Plunger and twist it down until the rod just pokes out of the nut. The Tool should now look like Detail 3.
On the inboard side of the tool, spin the nut that's inside the ratcheting wrench down until it's finger tight against the Bearing Spacer. Place a combination or box wrench onto the very inboard-most nut so it sets up against the washer. At this point, the tool should start to stand out from the knuckle on it's own and look like this:
Get all of the parts of the Tool lined up so they stack into a nice cylinder and tighten the ratcheting wrench just enough so that the Tool doesn't try to sag out of shape. If you try to keep tightening past this point, the threaded rod will just start spinning along with the ratcheting wrench. To prevent this, hold the wrench on the end to prevent the rod from spinning. By pulling the wrench towards the knuckle very slightly you will cause it to cam against the washer, allowing you to prevent it from falling off the nut without having to pay any attention to it.
Now tighten the ratcheting wrench.
A whole lot.
Long past the point where the small muscles in your shoulders are begging for mercy.
Tighten it until the tool falls off the knuckle.
Congratulations, you've just removed the bushing. Now hurry up and go do it on the other side.