I successfully installed a 2000 M-Coupe` rear sway bar on my 1998 318ti this past weekend. Below are the details of the swap.
1) Remove the spare tire. It's in the way. The exhaust does not need to be moved (if it's stock. I don't know about other brands)
2) Raise, and safely support the car.
3) Unclip the parking brake cables from the end-links of the sway bar (by hand).
4) Using a 13mm shallow socket and "wobble" extension or (Uggh) universal, remove the clamps and sway bar bushings from the car body. The clamps are "hooked-in" on the rearward side of the clamps, and there is only one nut to remove per side.
5) Using the same socket and/or open end wrench, remove the end links from the control arms. (there may be a clip in the way)
6) Man-handle the bar from the car. It EASILY snakes around the axles and exhaust with a bit of care.
7) Once out of the car, spray the end-link bushings with Silicone spray on both sides, where they attach to the sway bar. Bend the end links to get it worked under as good as possible. After it sits for a bit, the end-links should twist right off with no tools.
Spray the ends of the "new" sway bar with silicone, and slide them on the end-links exactly as they came off. (It helps to place them sie-by-side on the ground, and make sure to do one side at a time to prevent mix-ups)
9) Snake it back under the car as it was.
10) Spray the new bar bushings with silicone (unless you are re-using the old ones, but you wouldn't do that would you???) and place them in the aproximate final location. Place the new brackets over them and hook the rear side into the body.
11) Getting the nut on the stud is a bit tricky. I used large channel-locks to compress slightly the bracket and get it on the stud. Once it's cought, use the channel-locks to slide it on enough to catch the nut (dont cross thread it!!)
12) before you crank the bracket down, line up and bolt in the end-links. It may take a bit of twisting to line them up.
13) tighten the body bracket nuts fully, re-install the spare (after checking proper inflation, mine was low), lower the car and enjoy it!
Total work time: 45 minutes. If your car is a rusty mess underneath, I would invest in all new hardware, and expect to waste more time under there.
I ordered the bushings and brackets from the dealer for $28.00 or so.
Have fun!
PS the ti sport has a 13mm rear sway bar. The M Coupe` is 19mm.