We finally installed the M Performance Suspension kit on our 2nd attempt.
Our 1st attempted ended in a failure because we applied the M10 (steel bolt) torque spec to the top hat to strut tower M8 (aluminum) bolts about 2 weeks ago. It sheared the M8 aluminum bolts inside the top hat which we were able to extract after disassembling the spring strut assembly due to the taper direction.
Here are some pictures and comments in *rough* (not exact) order... This is not meant to be comprehensive. It is meant to supplement the official procedures found in either ISTAD and/or Bentley Service Manual. I have posted the ISTAD PDFs earlier in this thread.
Front Suspension
Do not re-use any bolts/nuts that the manual (PDF or Bentley Service Manual) states to replace.
Make sure when you position your car on a lift, you account for the fact that your car may sit lower once you replace the suspension.
Unclip your ride height sensor.
Remove the brake hose clips.
Remove all the lines/cables/wires.
Remove the nut securing the tie rod links to strut. I used a 3/8 electric impact to remove, but I used go-thru sockets and an alley key for the re-install.
Remove bolt securing steering knuckle to strut. You'll need a 16mm and 18mm socket.
This will allow you to remove that bracket which previously secured a lot of your wires.
Support the weight of the front hub assembly using a jack.
Remove the top hat to strut tower bolts along with the strut brace to top hat/strut tower Torx bolt. The Torx bolt removal can be done with a standard hex socket but we ended buying inverted Torx sockets just to be safe. I believe it was either an E18 or E20 socket (more likely E20 socket) that worked.
Using the knuckle spreader tool so that the knuckle isn't clamping to the bottom of the strut.
Make sure you have protected the paint around the edges of the front quarter panel.
Push the entire hub assembly as far downwards as possible. This will probably require 2 people: 1 to push the hub assembly down and 1 to guide the spring strut assembly out of the hub/knuckle.
Remove the spring strut assembly out. You may need to rotate either the top hat or the assembly to avoid scratching the paint.
Re-install in reverse order. Follow the torque specifications in the PDFs I have posted earlier.
The install should look somewhat like this:
Rear Suspension
The install of the rear suspension is much easier.
Remove your rear control arm covers.
Unclip all your wires/hoses to allow for move vertical movement of the control arm.
Place a jack underneath the rear control arm and apply slight force upwards on the control arm. This will help you remove the strut to control arm bolt. Remember to counter hold the other side of this bolt during removal.
Remove the strut by using inverted Torx sockets on the three Torx bolts connecting the top hat to the strut tower.
Now it's time to remove the spring. Take your jack and apply significant pressure on the bottom of the control arm. Make sure you're not placing the pad directly underneath the rear hub because that will not allow the control arm to clear the rear hub. Position your jack pad the way I have done two pictures above.
Now remove the bolt connecting the rear control arm to rear hub. If I remember correctly, you needed a 20mm or 22mm socket for this. Remember to counter hold the other side of the bolt/nut while you do this.
This part was challenging. Everytime we were in the process of removing this bolt, it would clear one side of the control arm and then the bolt would be forced at a weird angle that prevented a clean removal. You'll have to play with the jack to get the alignment right. An impact wrench will definitely make this part a lot easier.
Once you remove the bolt, allow the control arm to drop. You may have to pull it down a bit and then you'll be able to remove the original springs.
Re-install is in reverse order. As you jack up the control arm back into position with the new spring seated properly, you may need to either push or pull the control arm forward/backwards to get the hole lined up for the control arm to rear hub bolt. A bolt alignment tool may help you do this quicker.
Don't torque these bolts to spec yet. We'll do this once we have the shock installed and used the jack to apply enough force that the spring is compressed to what it might look like once the car is back on the ground.
Install the strut by hand compressing it so you can insert it back into position. Seat the top hats and secure those Torx bolts into the strut tower. Align the bottom of the strut to the holes in the control arm. This will probably require you to rotate the strut a bit. Now use the jack to position the control arm in such a way that the strut to control arm bolt will slide right through. Torque the Torx bolts at the top hat.
Compress the control arm a bit more with the jack and now torque down all your bolts.
It should look like this:
Review of BMW M Performance Suspension Kit (vs. original 704 passive Sport Suspension with 77,000 miles)
It's a huge improvement!
Body roll is significantly reduced. The floaty feeling of the original Sport suspension is gone. There's significantly more cornering grip and much better control through successive corners like S-corners.
Traction is also increased. There's almost no DSC intervention when exiting out of corners hard. Having the M Performance Limited Slip Differential is a contributing factor as well.
Braking is slightly improved. When you apply the brakes, the front end dips less which means that weight transfer is being applied more efficiently.
The noise and vibration has increased but it's not significant. The bright side is that the engineers at BMW have determined the optimal point where handling is significantly improved but noise/vibration/harshness is only slightly increased as far as a spring/strut combination. You'll be hard pressed to find a better spring/strut combo. High end coilovers such as Ohlins Road and Track and AST 5200 will still be better.
I'm headed out to a HPDE at Summit Point in a few weeks and will report back.
Here's a video after the install for your viewing pleasure: