Along with my new front brakes I was much in need of rear shocks. With 102k on the clock they were pretty bad, not much rebound at all.
I did the fronts about 25k ago so finally the rears. To do this procedure you'll need the following from my experience:

-floor jack
-jack stands
-19mm wrenches and/or sockets
-13mm socket with extension
-17mm deep socket
-vise grips
-spring compressors (I HIGHLY recommend these!)

After jacking up the car remove the rear wheel and secure with a stand. You'll need the jack later on so it needs to be free.

With a 13mm socket loosen the 3 mounting nuts in the wheelwell up top:
<img src="http://i234.photobucket.com/albums/ee127/islingtonboy/shocks1.jpg">

Next loosen the bottom long bolt with 2 19mm wrenches. I recommend placing your floorjack under the bottom of the shock with a slight bit of tension and then pounding out the long bolt after you've removed the nut by using a drift.
Once the bolt is out, lower the jack and the whole shock unit will drop down and can be removed:
<img src="http://i234.photobucket.com/albums/ee127/islingtonboy/shocks2.jpg">

We marked the whole unit with red paint dots as reference to how it is oriented. You don't need this many dots but definitely one dot per part so you can visually make sure they're all in place when it goes back together.

Now with the unit free of the car I recommend putting on spring compressors to keep the top cap from flying off when the nut comes off. There's not a whole bunch of tension but enough to give you a surprise! After they're in place, use a 17mm deep socket and vise-grips on the shaft between the springs to keep the old shaft from turning while you loosen the nut:

<img src="http://i234.photobucket.com/albums/ee127/islingtonboy/shocks3.jpg">

Now with the nut off you can disassemble everything. Keep track of the order and orientation of all parts. Along with my new Boge Turbo Gas shocks I also had a new bump stops/dust covers for the shafts, my old ones were cracked:

<img src="http://i234.photobucket.com/albums/ee127/islingtonboy/shocks4.jpg">

Before reassembling you need to remove the spring perch from the old shock. MAKE SURE (!!)you have this oriented correctly or you'll have a hell of a time getting it back together. We actually put the first one back together and back in the car before realizing our mistake, cost us several hours of frustration! This is the correct way:

<img src="http://i234.photobucket.com/albums/ee127/islingtonboy/shocks5.jpg">

This spacer is important, don't forget it!:

<img src="http://i234.photobucket.com/albums/ee127/islingtonboy/shocks6.jpg">


<img src="http://i234.photobucket.com/albums/ee127/islingtonboy/shocks7.jpg">

Now the top cap goes on, make sure the recess in the bottom of the rubber cap matches the end of the spring coil, it must seat in there so be careful and take your time:

<img src="http://i234.photobucket.com/albums/ee127/islingtonboy/shocks8.jpg">

With the everything together you should be able to get the new top nut on and threaded. You'll probably have to CAREFULLY use vise-grips on the shaft up high to grab it while you tighten. Don't mark up the shaft or you could damage the shock internals. It's very tough to tighten the top nut without holding the shaft however:

<img src="http://i234.photobucket.com/albums/ee127/islingtonboy/shocks9.jpg">

Now reinstall the whole unit. Using your floor jack again, first situate the top of the unit so you can at least grab one nut on its threads. Once you've tagged one, pump up the jack to bring the two other holes up and install the other 2 nuts. Tighten everything down and then the tough part....
You'll have to use your floor jack to lift up on the bottom of the shock to line up the shock mounting hole to the suspension mounting points.
It's probably a good inch or two you need to raise the new shock. The floor jack is indispensible for this and you'll need to manuever the shock assembly to get everything to align. An extra person or two is really useful for this. Once its aligned, drive the old bolt through, tighten her down and think of all the money you just saved!!

 

Nice writeup! Add to FAQ!

 

Nice pics, great write-up.

 

Instead of using a socket wrench on the top nut, I recommend using a 1/2" drive air impact gun...if you've got air and air tools.

Then you just blast that nut right off and back on.

I don't think I used my spring compressors on these. I think I was able to just stand over the assembly and push down on it while getting that top nut started.

 

@islingtonaudi,

I was Replacing my stock springs on my C4 Wagon with some H&R super sport springs i followed these exact steps to remove the strut then I just compressed the spring off instead of changing my shocks. Got em in perfect, Thanks alot for the perfect walkthrough! really appreciate it!