• lug wrench
• 2+ ton floor jack
• 2+ ton jackstands
• various 1"x4", 2"x4" and 4"x4" wood scraps
• ball joint puller
• rags
• pointy nose pliers
• metric socket set
• weatherstrip cement
• utility knife or Dremel (for removing spring pivots)
• tape
• "Lowrider" by War
• hacksaw
• spring mount upgrade (for 84-87 Corvettes)

Front:
3 to 4 hours

Rear:
30 minutes

The car must be lifted in stages to reach this height.  If your jack isn't low profile enough, try driving your Corvette's front tires onto some 2x6s first.  The Z51 spring is stiffer and therefore less curved than the base spring.  Base model vettes must be jacked higher than shown in the photo.  Before you do anything, place the car in reverse gear or park, set the parking brake, and you might as well block the rear tires for extra safety.  First, break the front lug nuts loose.  Open the hood too; it'll be more difficult when the car is jacked up sky high.  Next, place a 1x4 piece of wood on your floor jack (to protect the spring channel), and center the jack with the frame, not the engine & crank pulley, which are offset to the side.  When you've nearly reached the jack's maximum lift, carefully set the jackstands in place.  I prefer to locate them inboard of the factory jacking points, where the folded metal frame curves inward away from the rocker panel.  Avoid kinking the nearby brake lines, parking brake cable, and fuel lines.  Lower the car onto the jackstands, then add a 4x4 or extra 2x4s onto the floorjack, raise it up higher, raise the jackstands, and set the car back down on them .  You may need to set the jackstands on wood also if you don't have the taller 3-ton jack stands.  Notice I placed the front tires under the car for added safety.
 

Disconnect the sway bar from both sides and rotate it out of the way.  If you have ABS, you should unbolt the sensor at this point.

Place the floor jack under the lower control arm, parallel to the spring, NOT perpendicular as shown in the photo.  Beware of the Zerk (grease) fitting on the lower ball joint. Use wood to protect the soft aluminum control arm.   Raise the jack until the shock begins to move.  Now the shock can be unbolted.  Remove the cotter pin and metric castle nut from the lower ball joint.  Use the ball joint puller to remove the the steering tie rod and lower ball joint.  Swing the knuckle assembly out of the way and support it. 
 

Next, lower the floor jack slowly.  The spring still holds a massive amount of stored energy.  If the jack isn't placed parallel to the spring, it will side load the jack as it lowers, potentially damaging the jack, and toppling it over or spitting it out at you.  I did it the wrong way on this side and got lucky.  When the jack is all the way down, the spring is unloaded.  You may need a prying tool to pop the spring end out of the control arm.

Now, repeat all this on the other side.

Next, remove the metric spring retainer nuts.  There are 2 on each side.  The bolt may spin, and it's virtually impossible to get to it.  This is where impact tools would come in handy, or small hands.  Set the retainers aside, as they may need to be modified.  This is discussed later in the procedure.  Earlier Corvettes have 1/4" thick aluminum spacer plates that will come out with it.  These should be discarded for the maximum lowering effect.

Before attempting to slide the spring out, cover the ball joints with some old socks.  You'll have to really wrestle it out of there.  Try working it back and forth, and twisting it around the ball joints.  If all else fails, you can remove one of the lower control arms.

Pop the stock spring pivots out, and cut down the rubber to the surface of the spring.  A Dremel tool with a drum sander may speed up the process.  Be careful not to gouge the spring, as it is composite, and any damage will weaken it and expose the fibers to water and debris.

I glued the new spring wedges using the recommended 3M weatherstrip cement.
 

----------- UPDATE  -----------

The 3M adhesive failed after 2 years.  This resulted in the wedges coming loose and damage to the spring.  I reglued them with a 2-part marine epoxy this time. 

Tape the wedges to the spring to ensure proper adhesion.  This is the longest part of the installation, waiting for the glue to dry.  But, while you're waiting...

why not clean up all those pretty aluminum suspension pieces?  It would be a good time to paint your rotor caps and calipers too, which I didn't do until at a later date.  Also, take this opportunity to lube your control arm and sway bar bushings.

Since the aftermarket wedges are lower profile than the factory pivots, the spring will be located closer to the top of the spring channel, which is the load carrying surface.  This photo shows the difference in height, approximately 1/2 inch (including the aluminum spacer plate.)

Mid America's installation instructions recommend that owners with stamped steel spring retainers purchase the late-model aluminum styles ones.  The Mid America part number is 602714, and they retail for $29.99 as of this writing.  I chose not to purchase these for my '85, instead putting rubber spacers into the spring retainer bracket itself, so that when tightened down, it still held the spring in firmly.  To this date, I have not experienced problems with this method.

I then crammed the spring back into the channel with the wedges still taped up, to prevent them from coming dislodged.  Once in place, I could push the spring out slightly to either side enough to remove the tape. 

This image shows one of the new spring wedges as the retainers are being tightened into place.  There are depressions in the load bearing surface of the frame where the wedges seat against.  You may be thinking, "wouldn't it be lower if there were no wedges at all?" but it is essential that wedges at least 1/4" tall are used.  Otherwise, the spring will contact the metal frame, causing damage to the spring, messing up the spring rate, and altering the spring's designed purpose.  The pivot points are essential in establishing the spring rate, and their location determines the spring's anti-sway ability.  The Corvette is not a true IFS (independent front suspension) car, and the spring is designed in unison with the sway bar to provide turning stability.

Read this article for a more detailed discussion of the front spring design.

The remaining assembly is simply the reverse of disassembly.
 

The rear is quit simple to lower.  It doesn't even necessitate removing the rear tires or lifting the car. 

I placed the jack just inboard of the rear tire, and unloaded the spring from the bolt and nut.  Notice that the rear spring has a metal sleeve on the end, which is colored pink in this photo for visual purposes.   The floor jack is supporting the spring by this metal sleeve, and not actually coming into contact with the composite spring.  Placing wood on the jack and lifting the spring directly should work also. 

Next, remove the cotter pin.  The castle nut should come off easily, perhaps by hand.  The bolt and the bushings can then be removed.  Pay careful attention to the placement of the bushings when sliding in the new lowering bolt.  The difference in length of the new bolt and nut assembly determines approximately how much the rear will drop.

A 6" extension on my 1/2" ratchet was enough to allow access to turn the ratchet in the fenderwell above the tire.  This can all done with the spring still unloaded.  After locating the bushings, and centering them in the spring hole, lower the floor jack and continue on the other side.

If the rear sits uneven, adjust the nuts independently to even it out.  It is common on some Corvettes for the lowering nuts to be 1/4" or even 1/2" different from one another.