After almost a year of driving my Elise with a bad steering rack, I finally bit the bullet and replaced it this weekend with the help of JWA. I would like to add a couple of comments to the very useful instructions from post #35 by dbisbee in this thread.
Releasing the tie rod ends from the steering arms was not just a matter of tapping them with a hammer to get them to pop. Both of mine required the use of a tie rod end press type separator to get them to release. Don't use a regular "pickle fork" type remover unless you want to replace the tie rod end boots as these forks will destroy the boots.
To make sure you can get the new rack centered with the steering wheel, I recommend the following method. Before removing the old rack, turn the steering wheel all the way to the right (passenger's side) lock. Place a piece of masking tape over the gap between the steering wheel hub and the steering column cover on the right side and slice the tape where the gap is. This will leave one half of the tape on the cowl and the other half on the hub which will allow you to align the steering wheel to the rack at full right lock by simply lining up the two pieces of tape. Do the same with another piece of tape with the steering wheel at the full left (driver's side) lock. It also isn't a bad idea to place a third piece of tape at the top of the cowl and hub with the steering wheel and rack centered. Once you have placed the pieces of tape and cut them, do not disturb them for any reason until you are done installing the new rack. You will use these pieces of tape to make sure you have the steering wheel properly centered to the new rack.
Removal of the old rack was quite straightforward as per these instructions and we did not need to remove any of the rivnuts to accomplish this.
We had no trouble separating the rack pinion splines from the lower steering shaft U-joint, but we sure had a difficult time assembling the U-joint back onto the pinion splines of the new rack. We tried every position of the rack to the U-joint we could think of yet the U-joint would not slide on. Finally, in an effort to get some extra clearance at the lower U-joint, we removed the bolt from the upper column U-joint in hope that the lower steering shaft would slide further into the upper U-joint. It turns out that it will not slide any further, however the lower steering shaft slid out of the upper U-joint by accident and ended up on the floor of the car. This allowed us to to try fitting the now loose lower U-joint onto the new rack pinion and we found it would not slide on no matter how we positioned it. We became so frustrated at this point that we removed the new rack from the car and took it over the the work bench to try fitting on the lower U-joint. It turns out there was a burr on either the lower U-joint or the pinion splines on the new rack and after a lot penetrating oil and pushing we were finally able to slide the U-joint onto the splines. Repeatedly sliding the U-joint on and off of the splines finally allowed it to slide on freely. Now we reinstalled the new rack back into the car, reinstalled the lower steering shaft into the upper U-joint, and now the lower U-joint simply slid onto the new rack pinion splines with no effort at all. The moral of all of this is: When installing a new rack, remove the lower steering shaft from the car and test fit the lower U-joint onto the new rack before attempting to fit the rack into the car. This will save you hours of frustration.
My last tip is to install the new steering rack with the rack pinion turned all the way to the right (passenger's side) lock. When you go to install the lower U-joint onto the rack pinion splines, just position the steering wheel so the tape pieces you applied earlier with the steering wheel at full right lock are aligned. Slide the U-joint onto the rack pinion splines as far as you can, and before bolting in the rack or the lower U-joint, turn the steering wheel to the full left (driver's side) lock and check to see if those pieces of tape are aligned. If they are aligned, now you can bolt the rack into place and bolt on the lower U-joint. If the tape pieces do not align, you will need to remove the lower U-joint and index it as needed to slide it back onto the pinion splines with the rack at full lock and the corresponding tape pieces aligned. This is a much easier way to be sure you have the rack centered to the steering wheel than trying to measure tie rod lengths from the old rack to the new rack.
Hopefully these tidbits of information will save the next guy trying to install a new rack from the hours of frustration we endured. I also intend to disassemble my old worn rack to try to find what exactly wore out after only 4000 miles. If only my car had still been under warranty when my rack went bad.....