Warning: If you are not competent or do not feel comfortable doing any of these modifications or procedures, then please do not do so. I will not be held responsible for any damages caused by a result of your actions. Now on to the fun stuff!

Since I already have a procedure for changing rear shock mounts (RSMs) I will just give some impressions and talk about the design differences between these and the factory mounts.

Differences [Factory vs. Ground Control]:
The Ground Control (GC) shock mounts utilizes polyurethane bushings to dampen vibrations instead of rubber like the factory RSM uses. One advantage here is that urethane is a much stiffer the rubber so it can handle the abuse of a stiff damper. These units utilize what GC calls a horseshoe reinforcer plate with studs. Basically, it is a set of bolts welded to a reinforcing plate. This has one big advantage over the factory setup. It allows removal of the shock and RSM through the wheel well. Instead of having to tear apart the trunk to gain access to the RSM bolts and to loosen the center shock bolt, you can remove it all from underneath the car.

Instruction Notes:
Installation was an absolute snap. They install just like the regular mounts, except that the horseshoe plate drops through the body and then through the RSM. Then use the included washers and nylock nuts to secure the RSM to the body. There has been a bit of discussion about whether or not to use the Z3 reinforcers with the GC units as the already have the horseshe plate. I personally did not install them with the Z3 plates. Then once the shock goes through the RSM, be sure to use the large washer included between the shock and bushing. GC's included instructions state that for Street use, the bushing should be installed with the step facing towards the shock. For race applications, the bushing should be installed with the step facing the RSM. Once in place, drop the other bushing on top with the step facing upwards (away from the RSM). Be sure to reinstall with the factory washer on top. You may want to replace the shock nut as it is a nylock and designed as a one time use fastner. GC recommends a torque of 10 ft lbs, but states this is difficult to measure. So give it about an extra full turn to two turns (for really aggressive applications ie. racing) after you can no longer wiggle the washer with your fingers any more.

If you need any more specifics, check out my page on the full RSM installation.

Impressions:
After about 1,500 miles on the new mounts, I really like them. There is little to no increase in noise, vibrations, or harshness (NVH) of the ride. The units are incredibly solid feeling and look to be very well designed. I don't think that I'll ever have to replace them again. If I do, GC pays for it with their lifetime warranty. Before there was very noticeable visual deflection of the e46 M3 mounts over even small bumps. Larger bumps resulted in very large deflections of the rubber mount. Now with the GC RSMs there is hardly any noticeable deflections. I think I might have seen it wiggle a little over an expansion joint.

Pictures:
A few things of note here are the horseshoe reinforcement place with studs and the stepped uerathane bushing.

Update [03.05.03]: Here is a picture of the mount from the wheel well.

Update [03.22.03]: Here are some pictures of the mounts installed as designed.

You'll need something like this to get the mounts off the Bilstein shocks.

Now for the new stuff. Occasionally, when going over sharp drop offs I'll run out of droop travel. I flipped the shock mounts, so the hump now points down.

Update [04.01.03]: I installed the summer wheels/tires today and I can say that the GC RSMs do make a bit more noise now. I'm sure the stiffer sidewall of the RE950's has a lot to do with it. The noise is like a deep thud when going over sharper bumps. Not that big a deal and I'm sure after a few days of driving I won't even notice it any more.

Update [04.23.04]: After installing the subframe reinforcements the ride height was raisied. So I lowered it back down. Now I have enough droop travel and was able to flip the RSMs back to the way they should be.

Update [05.14.04]: Ride height is back up to 11 3/4" in the rear and I'm running out of droop again. So, I flipped the RSM's again. The Z3 plate and GC halfmoon plates are out of the Rogue Engineering plates are in.