Lowering Springs & Rear Deck Removal/Installation
Basic, unedited instructions.
First, start by removing the rear seat. Press the two black release tabs mounted to the floor on the underside of the seat cushion. Pull up on the front edge of the cushion to release and remove. This will expose three (3) 12mm bolts along the bottom of the seat back. Remove the bolts and pull straight up on the seatback to release the two hooks at the back. You should be at this point by now:
The red circles are the quick-release clips holding the rear deck on. Pop the middle of each one into the "up" position with a small screwdriver and pull up on the raised middle section to remove them.
Next, the brake light will need to be removed. Use a large flathead screwdriver with 2-3 layers of masking tape at the tip (to prevent gouging the rear deck) to pry the back end of the brake lamp up. Get your fingers underneath it and pull up firmly while pulling it toward the front of the car to release it. It should pop right out. If it hasn't been removed before, it might be a bit stuck. There's not much slack on the harness connector, so don't pull it too far.
Disconnect the electrical harness underneath and remove the brake light.
Next, remove the rear deck cover by firmly pulling upward at the middle towards the rear glass. Once it's up high enough to clear the plastic retaining pins (circled in green and blue), it can then be pulled out. I didn't pull up high enough before yanking my rear deck cover out and, as seen below, I broke one of the retaining pins off (circled in green).
Once the rear deck cover is out, you'll be presented with a hole on each side of the rear deck speakers with a removable cover over it.
And inside the hole...
You shouldn't need a swivel adapter, but for some reason, I remember doing this same job on my '95 model and needing one because the access holes were smaller or not shaped the same way. They are 14mm nuts. Don't remove them just yet. That comes later.
Once the rear axle is elevated and the wheels removed, remove the large bolt and nut at the base of the strut and also the small bolt that holds the ABS sensor wire to the side of the strut casing. Both are pictured below. The large bolt may not want to come out easily once the nut is removed. Try using a screwdriver and hammer to tap it out. Putting weight on the axle so it droops lower also will aid in removing the bolt.
Here's where it can get tricky. After removing the bolt, the axle will now have to come down low enough so that you can get the fork to clear the lower end-link. You want the forked end of the strut to wind up behind the rear axle, not in front of it. Having two people makes it easy. One stands on the end of the axle while the other pulls the strut base towards the rear of the car. Alternatively, a pry bar or wood plank can be wedged between the strut and front link while standing on the axle to get it to clear. Once you have the fork clear of the lower link, position a floor jack underneath it as pictured below so that it isn't hanging.
Next, remove the 14mm bolts exposed earlier when the rear deck cover was removed. While ensuring that the ABS wire doesn't get snared, slowly lower the floor jack and remove the strut. Now, you're at this point:
Here is another problem you'll run into. Here, I'm using an impact wrench to remove the 17mm nut from the top of the strut assembly. A traditional ratchet should work as well, but the shaft will spin as you turn the nut. Preventing the shaft from spinning is difficult without a large bench vice and using something like vice grips with radiator hose on each end to prevent shaft damage. With the impact wrench and air compressor, it's no sweat.
The top mount and shaft are keyed so that it only goes in one way. This means the nut can be broken loose while on the car then it can be removed once the assembly is off the car. However, this only works on the front because the nut can be exposed in the engine bay by removing its plastic cap. The 17mm nuts on the rear struts are covered by a metal plate when mounted, so that's not an option.
Before you go removing that top nut on any strut assembly, you must use a spring compressor tool similar to the one shown below. The factory spring must be compressed enough so that the pressure on the top mount is relieved before removing the nut. If the spring isn't compressed first, the assembly will come apart explosively causing possible injury. While the stock springs are under a fair amount of tension when mounted in an assembled strut, lowering springs such as the Eibach ProKit are physically shorter when unloaded so I didn't need to use the compressor on them before disassembly so the spring compressor tools in the photo below are purely for illustrative purposes.
Before compressing the spring, make note of the orientation of the top mount. It might be keyed, but the shaft will spin easily so it will go back together in any position you please, but it will only go back on the car one way. Marking the strut and the mount with a wax pen before disassembly might be a good idea. When the reassembled strut is ready for reinstallation, it's quite a disappointment to get the strut back on the car and realizing that the fork at the bottom is turned the wrong way requiring removal and disassembly of the strut to correct the orientation.
Once the top mount is off, the bump stop / dust boot will need to be removed before the spring can be removed. The stop will come right off the shaft and past the retaining ring if you pull hard enough. A little oil or liquid soap can help ease them past. If the boots/stops are damaged or deteriorated in any way, I highly recommend replacing them with new ones from Mazda at $12 each when swapping springs. Also, the installation instructions for the ProKit are written for the Millenia S in mind and advise to cut a third of the bump stops away before reassembly. I would advise against this. Instead, I would recommend the use of 5/8th inch coil spring spacers on the front axle along with intact bump stops for the ultimate in performance and comfort. Millenia L owners don't need to use coil spring spacers on the front. The ride height on the front axle is already a half inch higher when the ProKit is installed on L models due to the lower weight of the 2.5L engine/gearbox, so intact bump stops will work fine with that application without coil spacers.
There is no need to cut the stops on the rear axle of either model. However, the rear axle could stand to be more level. Once you get those Eibachs on, you might notice that the right rear corner is nearly a half inch lower than the left rear corner. That's because the factory rear springs have unequal spring rates to compensate for the right-rear being a little heavier. The Eibach ProKit uses the same spring rate on both sides on the Millenia, so the ride height will differ between the left and right. Adding a 3/8th inch spacer on the low side will equalize the static ride height in the rear.
Installation is reverse of removal. To get the bump stops back on after putting the spring in place, use the largest deep socket you can find and use it and a hammer to get the bump stop past the retaining ring on the strut shaft.
I don't have any pics of how it's done on the front axle yet, but it's very similar to the rear. The front struts have the same three 14mm bolts at the top and connects to the lower link just as the rear does There's also an ABS wire bolt just like the rear as well as two 10mm bolts that connect brake line to the strut shaft. Once those are off, it's the same. Support the bottom with the floor jack, remove the three top bolts and lower it down and remove it from the car clearing the ABS sensor wire and brake line. The fronts are easier to get off than the rears but harder to get out. You'll know what I mean when you cross that road.
[Mazda Millenia Lowering Spring Installation Guide - unrevised]