I followed Mr.5's DIY to replace the mid brake lines (here:http://www.e90post.com/forums/showpo...1&postcount=17
One of the more challenging mods I've worked on to date. My hands paid the price because there isn't much room to work with.
I went with Stoptech Stainless lines. Great quality but I wish the lines had the "star design" at the hose connects that the OEM lines have to prevent rotation as you tighten down the lines. ECS lines have this with their "exact fit" lines. It wasn't a huge issue, but given the challenge in swapping the mid lines, every bit helps. The install for the lines to the calipers are a breeze.
Tip #1: depress the brake pedal about 2 inches using something to wedge between the seat and the pedal to prevent significant fluid loss while you are wrenching away. The fluid loss was minimal during the nearly three hour install (second time around will go quicker).
Tip #2: You need a quality Flare Nut Wrench 11m to loosen and tighten the hard lines. The metal is soft and will round off very easily. I bought 6 identical wrenches from pep boys, out of the six only one had the tolerance I was comfortable with. Also, I hit the bolts with Liquid Wrench (any penetrating oil should work) the day before to ease breaking the nut free. I loosened it to the point I could use my fingers to remove the line.
Did a full flush with Castrol SRF brake fluid using a Motive pressure bleeder. I always pull the old fluid from the reservoir with a measuring syringe as there is no reason to push old fluid through the system (don't pull too much and add air). I then top off the fluid reservoir with fresh fluid and attach the pressure bleeder (I don't add fluid to the pressure bleeder). Start with RR, RL, FR, FL (Facing the rear of the car).
I bled the rear lines first. Starting with the RR line until nearly half the reservoir was depleted, released the pressure AT THE BLEEDER TOP, then refilled the reservoir and bled the RL line. Refilled the reservoir again and bled the FR and FL (Refill was necessary due to the length of the lines).
The Feel: I was skeptical at first, but the feel is great, tremendous actually. Much more brake-by-wire feel. The OEM lines are very good, but the difference in pedal feel is significant. The true test will be at the track, I expect consistent firm pedal feel for longer than can be achieved with stock lines.
Running Stoptech ST-60s with Pagids RS29s on the front and Stock Calipers and RS-7 Pagids on the rears.