Shocking! Part I...

What a wonderfully utilitarian little car, this Z3 Coupe - look how nicely a full set of shocks and springs fits into the back!

Replacing the shocks had been on my list for a while - in fact, it was on the original "punch list" that Jack Miller and I drew up in the first weeks of owning the car.  Jack had told me that, since the shocks on the car were not leaking, he would pass them for state inspection as long as I promised to replace them.  The time has come to do just that.

I did a lot of research, and decided to install Koni shocks.  That was not the choice I first expected, since the conventional wisdom is that Bilstein shocks are the way to go on BMWs.  But these new high-tech FSD shocks from Koni really caught my attention, and I decided to give them a try.  I ordered a set, and waited, and waited, and waited...

While impatiently waiting, I also started second-guessing my decision.  I had decided to stay with the stock springs, but then I saw Matt Sware's Z3 M Coupe, and it reminded me just how much better these cars look a little closer to the ground.  I finally called Bavarian Autosport and asked about my Koni's, and was told, "We're waiting for them to be manufactured.  Not much call for shocks for Z3s, so we have to wait until Koni gets around to making them."

I also noted that, for almost exactly the same price as the Koni's, BavAuto had a set of Bilsteins paired with their own branded springs.  They were in stock, so I switched.  Here they are, with a bunch of shock mounts and bumper pads I ordered to go with:

On an ordinary car, all the hard work is at the front.  Changing rear shocks is just a matter of a few nuts and bolts.  But, this was another place where the BMW Department of Ridiculously Complicated Engineering sprang into action, and you have to remove a significant part of the interior trim at the rear to just to uncover those two nuts on each side that hold the shock mount in.  Fortunately, I found a marvelous, step-by-step procedure for that process, at this link:  http://www.ex-parrot.com/pdw/mcoupe/rsm.html

I won't duplicate his work here, but I will include my version of a shot he took - just look at all the stuff I had to remove from the interior just to get started!

Once all that was out of the way, here's what I could see through the rear decklid:

See the little round black dome under the side window?  Either side of that, there's a nut, and that's what holds the shock in.  I started on the driver's side, and dropped the shock out.  It was really dead - I could easily compress it with one hand.

To replace the spring, I followed the procedure in the big Bentley manual, which has you detach the half-shaft from the differential to allow the trailing arm to drop low enough to change the spring.  It worked great on the driver's side - here it is with the new shock and spring in place:

Now, what's a project without the opportunity to buy a new tool?  It turns out I really needed one for the shock installation.  The shock's shaft has a hex-head hole in the end.  You insert an Allen wrench in that to keep the shaft from turning while you're tightening the nut.  A regular socket wouldn't allow that to happen, so I happily went to Harbor Freight and bought this fancy set of sockets and matching ratchet that allows the shaft to pass through:

You tighten the nut after the shock and mount are in the car - here's what the tools looked like in action (except that I removed my hands to take the picture):

Yes, I know I could have done this with a box-end wrench too - but I kinda wanted that cool socket set!

So, great - now to do the passenger side.  And there... another case of Somebody Has Been Here Before.  The half-shaft is held in place by six bolts with very special heads, a splined style called External Torx.  Somebody had hammered one of them with an air wrench (all of them actually), and when I tried to loosen it, the head rounded off.  I could NOT get it loose.

So finally, I tried the other method I had read on the Internet, to remove the nut on the anti-sway bar link, and push the trailing arm down and pry the spring out.  It worked!  So the new spring and shock are in, and I've ordered new bolts for that trailing arm.  I'll replace the five that came out, and leave the rounded one until next time I'm at Jack's shop - I'm sure he has better tools for dealing with getting it out.  But I will do that, because someday that half-shaft will need to come out, and I'd rather deal with the bad bolt now.

I'll probably wait to reinstall the interior trim until I've done the front end as well, and drive it to make sure all is well.  I'd rather not have to take it all back apart if it turns out I did something wrong!