[e90pilot]

A while ago, I installed 135i brakes on my 325i. I had a really big issue with air in the system. I replace the all the rubber brake lines with steel braided lines. I was told by that's it's really easy to get air into the DSC motor and it's really hard to get it out. I bled the brakes several times and bubbles came out every time. I went on a dirt road and activated ABS several times for a several seconds at a time. Finally on the fifth bleed attempt, no more bubbles come out of the bleed nozzles anymore but the pedal feel isn't really was I was expecting. I went to a dealership and test drove a used 135i and it was better pedal feel than mine. Mine still feels a little soft. I checked realoem.com and the 135i has the same reservoir, master cylinder, and brake booster as mine. Is there something I missed? I'm using factory pads and Stoptech Power Slot rotors.

[Express]

what is your method of bleeding?

[e90pilot]

I first used the good old pump the pedal while someone opens the valve. The last attempt was with a pressure bleeders.

[Express]

i use a mityvac vacuum bleeder and my brake pedal is rock hard. you shouldn't have a soft pedal with the pressure method...

what machine did you use?

[e90pilot]

I've also heard that vacuum bleeders are better too. I forgot the exact brand but it's just a standard pressure bleeder; a plastic bottle with a hand pump and a reservoir cap. No more air is coming out of the nozzles. I'm wondering if it's stuck somewhere. I also tapped the caliper with a rubber mallet. It's not super soft, just not as solid as I thought it would be with a solid caliper, steel lines, and Motul RBF 600.

[Express]

use reg. dot 3/4 i cant remember what it takes.

try the vac method. amazon sells the pumps for 36 bucks, or, ill mail you mine and just mail it back when you are done. that way you get each caliper separately.

[Tzu]

Dot 4.

[e90pilot]

BMWs usually take dot4. I use the motul on the track. The stock fluid fades pretty fast. Just 3 laps a Laguna Seca which is really hard on brakes will turn the pedal to goo. The Motul holds out pretty well until the pads overheat which I discovered is about 3 laps after that.

[rigdowntex]

If you did get some air into the DSC valving you may just have to take it to BMW and have a complete flush of the system, don't know how or what they use but I had too after a caliper and steel lines done at a competent speed shop here. My cruse control worked intermittently after install and codes pointed to DSC malfunction, the BMW mechanic said it was air in the DSC and was right, my pedal feel was always OK even with the malfunction, keep bleeding or <choke> take it to the stealer, 200 bucks just so ya know.....

[e90pilot]

I know they dealership runs a test on the DSC that runs the motor. They also use a vacuum bleeder. You can do it with a GT1 tool. Don't know anyone with one though. I might just take it to some place. I still have one unopened bottle of fluid. I'm not paying to $200 though. There are plenty of shops around here that should know how to do it properly.

Or maybe I'm just being too picky. What if that's just the way it is? I just don't like how brake pedal sinks below the throttle with moderate braking. It makes rev-matching difficult.

[Express]

do you want my vac bleeder?

[fdriller9]

If air enters the DSC hydraulic unit, bubbles can adhere to the walls/internal valves. You'll need a BMW scan tool to bleed the system. It will create small pulsations/vibrations to loosen and flush out the air bubbles.

[e90pilot]

Sure, but it might be a while before I have time to work on it again. Does your brake pedal go below the throttle?

[The HACK]

"Fixed" calipers are notorious for allowing air to be trapped. I remember installing a set of StopTechs on a friend's car and the calipers had to be taken off and bled upside down a couple of times for all the air to be removed from the system.

If "symptom" persist, it wouldn't hurt to try it. Just make sure you put a used rotor between the pads so the piston does not unseat themselves.