Ground Control: Rear Installation

This procedure is meant to be a reference on the removal and replacement of the rear shocks, springs and shock mounts. If you read past this paragraph and you decide to apply anything that is contained within this reference you are assuming total responsibility and liability for your actions including but not limited to damage to your or someone else's vehicle or person.

It's important that you know your mechanic abilities. If you feel that this is over your head, don't do it -- get a professional to do it.

Prep work:
Record the ride height at all four wheels. Measure from the center of the wheel vertically to the top of the fender arch. On my 2000 Z3 2.8, each corner was at 14.5"

Make sure you have the needed tools at hand:

  • Trim removal tool
  • 3/8" drive metric socket set with various extensions
  • 1/2" drive metric socket set with various extensions
  • Torque wrench (10-80 ft/lbs will work)
  • Metric open-end wrenches
  • Pry bar (12"-24" long should do)
  • Hydraulic floorjack
  • Jackstands (2)
  • Gloves are nice to have
Interior work, upper shock mount access:
Raise the convertible top

Using interior trim removal tool (see photo), carefully remove the four trim buttons in the top well just below the rear window. These secure the carpet that covers the upper shock mounts. Using the proper tool will allow you to reuse the fasteners. You can also use a flat-bladed screwdriver to do this, but most likely you will damage the fasteners and have to replace them.

The top edge of the carpet is held in place in a downward-aiming 'C' channel. Starting at the front edge (near the door jamb), pull the carpet downward and away from the channel working around until you get to the opposite side.

Fold the carpet away from the rear "corners" to expose the upper shock mount bolts. The carpet will seem stiff, but folding it against its original shape didn't seem to cause any harm or creases.

Using a 14mm socket, loosen but do not remove the two (per side) flange nuts.

There is a soft rubber cap over the end of the shock; gently work that off the top of the shock and over the top washer.

Sorry about the poor picture, but you should be able to make out the two shock mount nuts/bolts (one partially out-of-frame), and the rubber cap over the end of the shock.

Lifting the car:
Chock the front wheels.

Using a floorjack on the cross-member just ahead of the differential, carefully lift the car until you can place jackstands under both rear jack points (just ahead of the rear wheels)

Lower the car gently onto the jackstands

Disassembly (per side):
According to some accounts, removal of the rear coils can be done without disconnecting the CV joint from the differential. The Bentley service manual explicitly warns that doing so may damage the CV joint. Everyone I've talked to since has said we wasted our time... no need to worry about this. Regardless, I've included the instructions below. Instructions specific to this will be highlighted with this color.
Remove wheel (17mm) -- Note the approximate height of the hub center off the ground.

Use the floorjack to support the rear trailing-arm

Remove (2) top shock bolts (14mm)

Remove lower shock bolt (17mm). Have someone hold the shock body to prevent it from dropping when the bolt is removed.

Using a 13mm wrench, remove the bolt securing the anti-roll bar to the trailing-arm. This makes subsequent steps a bit easier.

Support the inboard end of the drive axle using a piece of heavy wire or strong bungee cord

Using an E12 socket, remove the six bolts securing the upper CV joint to the differential. It will help greatly to have someone set and release the hand-brake during this operation.

In the photo, you can see the half-shaft unbolted and supported by a black bungee cord.

Note that the photo was taken after installing the Ground Control coils.

Gently lower the floorjack supporting the trailing-arm end.

The coil will still be under a small amount of compression, but it can be removed using a pry bar to lift and push the lower end off its mount.

Remove the lower spring pad (rubber); leave the upper bump-stop in place.

Re-assembly: pretty much done in reverse order
Again, instructions specific the half-shaft reinstallation will be highlighted with this color.
Parts familiarization: (left-to-right)

  • Height adjustment sleeve with the lower coil seat in place
  • Eibach coil
  • Upper coil seat
Place the height-adjustment sleeve (reddish color) over the lower coil centering post. Spin the coil seat onto the sleeve and tighten the locking bolt. I set mine so there was about 3/8" of sleeve above the collar, and this yielded a 1/2" drop in ride height. The amount of drop you experience will vary according to the spring-rate of the coils in your package.

Slide provided rubber seat around the upper bump stop (friction should hold it in place), and fit the coil around the bump stop. Align the lower end of the coil with the seat/adjustment collar.

Using the floorjack, raise the trailing-arm making sure the coil and seats stay aligned. Raise the arm back to the position noted earlier.
Bolt and torque the inboard end of the half-shaft to the differential hub and remove the cord/wire used to support it.
Re-attach the anti-roll bar... you can use the floorjack to help align the bracket to the arm.
Place the Ground Control upper-shock mount bracket in the top well with the bolts extending downward through the body.

In the photo, this is the 'C'-shaped piece with the two allen bolt heads. The allen bolts are pressed in place and will not spin. You will NOT need to use an allen wrench when securing the shock mount.

Note in this picture that the shock has been installed.

Thinking back, it might've been a good idea to use a small dab of silicone adhesive to hold the bracket in place.

The rear shocks mounts will already be assembled to the Koni shocks. Ground Control also pre-set the rebound adjustments for me.
Transfer the gasket from the original upper shock mount to the new Ground Control shock mount.

Position the upper end of the shock/mount up into the fender well so the bolts from the top-mount bracket extend through the shock mount. If you are careful, you can do this without having anyone hold the upper bracket in place.

Thread on the supplied lock-nuts and torque appropriately.

Extend the shock so the lower mount hole aligns with the mount on the trailing-arm.

Bolt the lower end the shock to the arm using the original bolt placing a washer between the bolt head and the shock.

NOTE 1: You may need to supply your own washers (12mm or 1/2" will do). Apparently, some cars have them, some don't. Mine didn't.

NOTE 2: There is some question as to whether the washers are required or not. I've talked with a number of people who feel they are not at all necessary in this application.

Torquing this bolt should be done with the suspension under load. This can either be done when the car is back on the ground, or you can use the floorjack to lift the trailing-arm until the jackstand is almost free. The driver-side is not too difficult to get to, but the passenger-side is partially obstructed by the spare-tire carrier.

The lower end of the shock is not in position in the lower photo. I just wanted to provide a wider view.

You can now gently lower the floorjack supporting the trailing-arm. I replaced the rear wheels when both sides were complete in case I needed to check measurements or make adjustments.

Fit the rubber caps over the top end of the shocks in the convertible top well.

Fold the carpet back into place making sure the top edge gets fitted into the 'C' channel.

Re-insert the four (4) trim fasteners by just pressing them into the holes until tight.

Double check that no tools have been left inside the top well.

Wrapping up:
Once both sides are complete, double check that all bolts have been properly torqued, and that the ride-height adjustment collars are in approximately the same settings. Mine were about 3/8" from the top and this yielded a 1/2" drop in ride height.

Replace the wheels are torque the lug bolts.

Using the floorjack, lift the car off the jackstands and pull them clear. Gently lower the car to the ground.

Take the car for a short test drive to settle the suspension in place.

Take note of the new ride-height and make adjustments as needed. This can be done as follows:

  • Jack up the side of the car to unload the suspension.
  • Loosen the adjustment-collar locking bolt.
  • Spin the collar to either raise or lower the coil seat.
  • Retighten the locking bolt and lower the car back to the ground.

Questions or Comments
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