As I prepared to do this DIY, I could not find a thread on the M3 forums about doing this. I did find one on the E90 forums but there were some interesting things I came across that I'd like to share.
First off, here is what was required to do the job.
SS brake lines - I installed the exact fit lines from ECS Tuning
This kit included all 6 lines. For the most part all SS lines are pretty much the same but what I liked about these is that the connector on the hard line side is keyed similar to the OEM lines. This keeps the line from spinning while you tighten the hard line coupling. I've heard that the Stoptech and the Goodrich lines do not have this feature so you'd need to hold the line with another wrench which is somewhat difficult in tight spaces.
You also need:
1L of brake fluid - I just used BMW OEM DOT4 fluid (2 bottles) since I'm not tracking the car
11mm flare wrench
11mm open end wrench
9mm flare wrench
Rubber caps for the hard lines (the ECS lines do not come with this).
14mm flare wrench
13mm open end wrench (for the front OEM line on the caliper side)
14mm open end wrench (for the rear OEM line connection at the caliper)
A pressure bleeder or someone to help you bleed the system after you're done.
17mm socket to remove the wheels
Jack and jack stands or a lift
Jack the car up on all 4 corners or put the car on a lift. Remove all 4 wheels with the 17mm socket. Don't forget to break the lug bolts loose before you get the car off the ground.
Use your 8mm socket to remove the 3 screws holding the plastic cover for over the brake fluid reservoir in place. It is on the drivers side of the engine bay near the windshield. You will see 1 screw on each side of the cover just under the windshield wiper and the third is near the rubber gasket over the firewall. After you remove this cover you will see that there is an electrical connection on the cover. Don't bother to remove it. There is enough slack on the cable that will allow you to just move the cover out of the way. Removing this cover will only expose the cap on the brake fluid reservoir.
Once the cover is removed, you'll see another plastic trim covering the rest of the reservoir. This cover can just be removed by hand. Removing it is not absolutely necessary but if you want to see what the fluid level is you'll need to remove it.
Now we're ready to start removing the lines. I started with the front. Before removing any of the lines, take note of how the original lines are routed around suspension components. You'll want to route your new lines the same way to ensure that the lines don't get kinked when the suspension moves. When removing the lines, remove the side connected to the hard line first. Use your 11mm flare wrench to loosen the coupling on the top side of the connection. The use of the flare wrench is important with the fasteners associated with the brake system as they tend to be soft and strip easily. Once broken loose, you should be able to back the coupling out by hand. When the coupling is completely loose from the brake hose connector, pull the connector away from the hard line and cover the hard line with the rubber cap to keep brake fluid from dripping out. After the OEM brake hose is disconnected from the hard line, remove the rubber bushing from the bracket just behind the caliper. Then you can use your 13mm open end wrench to remove the brake hose on the caliper side (I think it was 13mm but double check as I'm writing this a few hours after I finished the job). I used an open end wrench in this case because the rubber boot on the OEM line is too big for the flare wrench to slide over. You will need to spin the entire hose as you loosen the caliper side connection so stretch the hose such that it's vertical to give your self room to spin it without flinging brake fluid into your eyes.
Installing your new front SS lines should be done in reverse of removal. Connect the caliper side first, slide the rubber bushing into the bracket, then connect the hard line side. With the new lines, I was able to use a 14mm flare wrench to tighten the caliper side. Do not fully tighten the caliper side until the coupling on the hard line side is tight. This will allow for adjustments if necessary. When trying to reconnect the hardline side, you will notice a metal bracket around the hard line connection which has a star like pattern in it. On the ECS Tuning lines, there are protrusions on the connector which line up with this pattern. This keeps the line from spinning while you tighten the hard line coupling. If you don't have this, you will need to hold the connector on the new line in place with an open end wrench.
Remove the rear outside lines in a similar fashion as you did the fronts. Use the 11mm flare wrench to remove the coupling on the hard line side then plug the line with the rubber cap. Then use a 14mm open end wrench to disconnect the caliper side (again, verify size since I'm writing this well after I finished). For the rear, I found it easier to stretch the line towards the center of the car to loosen the connection at the caliper.
Install new rear outside lines in reverse of the removal. Nothing special here. I used a 14mm flare wrench to tighten the new lines on the caliper side.
Step 8 (optional):
If your kit came with the rear mid lines, I will let you know right now that it is a major PITA to put on and some say it has little effect on the final outcome. But if you're up to the task, this is how I did it. I removed the upper connection first using an 11mm flare wrench. Space it really tight in there so I couldn't turn the coupling more than a 1/4 turn at a time and thus lost quite a bit of fluid while it was dripping onto my garage floor. Keep an eye on the fluid level at the reservoir as you don't want it to drop below min. Refill the fluid if required. Once the upper connection is out, cap the line and remove the lower connection with the 11mm flare wrench. You shouldn't have to plug this line with a rubber cap since you already took out the outer lines and there should be almost no fluid in that section.
Step 9 (optional):
Install the rear mid lines. I found it easier to start with the upper connection first. It is also easier to start with the passenger's side line as it is further towards the center of the car than the driver's side and you will need all the room you can get. Again, since there is little to no room to maneuver your 11mm flare wrench in there, I could only turn it very little at a time. I also needed to flip my wrench over constantly to try and get the proper angle to allow me more room to turn the wrench. I even had to use an 11mm open end wrench intermittently when I couldn't get the proper angle with the flare wrench. Be careful when tightening with the open end because it's easy to strip the coupling with the open end. After the upper connections are tight, connect the lower connections with the 11mm flare wrench.
Double check all your connection points to make sure they are all tight. Don't try to over tighten since these connections are very easy to strip.
Now you're ready to bleed the system. The bleeder valves on the front calipers are 11mm and the rears are 9mm. Use your flare wrenches again to loosen the valves. I have a Motive pressure bleeder which works well but my brother was helping me and he had a pneumatic bleeder system which I liked better than the Motive bleeder. It was very similar to this
You connect the bleeder to an air compressor and connect the hose on the bleeder to the bleeder valve at the caliper (order should be passenger rear, driver rear, passenger front, then driver front). Loosen the valve and then pull the trigger on the bleeder. The bleeder will suck fluid from the reservoir and out the bleeder valve. The bleeder kit comes with a bottle you connect to the reservoir. The bottle is filled with new fluid to ensure that the appropriate level of fluid in maintained while you are bleeding. I went through all 4 sides twice to ensure all the air bubbles were out.
After I bled the system, I started the car and pressed on the brakes just to be sure pressure was being maintained in the lines. If your pedal falls to the floor or feels spongy, you could have air in the lines. Bleed again.
Reinstall the covers over the brake fluid reservoir.
Reinstall the wheels and tighten the lug nuts to hand tight. As you drop the car down, get it to the point right when the tire touches the ground but do not drop it all the way down. At this point, tighten the lugs to 89 ft-lbs. Once that is done, you can drop the car all the way to the ground.
This is also optional but a good bit of information. My brake fluid service indicator was on prior to starting the job so I needed to reset it. The brake fluid service indicator is not something that can be reset via iDrive. I used the method described in this video and it worked flawlessly.
I hope this helps others that are interested in this DIY. Total work time was about 3 hours with 1 hours being spent just on those rear mid lines. Some will argue that replacing the OEM rubber hoses with SS lines makes no difference on the street. I agree with that for the most part. During normal driving, there is no difference except at threshold braking. With the OEM rubber lines, if you stomped on it hard, you'd feel the pedal bounce back just a little which I assumed was due to the expansion of the rubber lines. With the SS lines, you don't feel that. The other plus with the SS lines is you don't have to worry about the lines bursting due to wear like you do with the rubber lines. I've heard of rubber lines bursting due to fatigue and you can imagine how dangerous that situation would be. For a $100, I thought it was worth the money. You should still check your SS lines for abrasions in the outer coating. If you see any cuts or exposure of the steel braid, you should replace the lines.
Sorry no pics because my hands were covered in brake fluid and I didn't want to touch my camera with that all over my hands.