Symtoms are soft brake pedal one pump and it is up to what it should be,installed are new TSW rotors Porterfield pads and s/s brake lines,bled the brakes with a dot 5 and pedal feel the same,we've now replaced the master cylinder and bled again and still have the same pedal feel,what next do i do.Mecanic says the lines dont have air they have been bled twice. 2003 cooper

 

How much fluid bled out when you replaced the lines? Did you partially depress the brake pedal while changing lines to prevent fluid from flowing from the reservoir? Did the reservoir run dry?

Sounds like you may have air in the ABS module? Once it's in there, it can be a bugger to get out. I have AutoEnginuity which has an ABS air bleed mode. The Dealer scan tool and some specialty BMW tools can do this also. Generic scan tools can not. Some folks have success by driving on dirt or gravel and locking up the ABS a few times (which moves the bubbles around) - then doing another bleed.

 

The brake pedal was not depressed to change the lines but little fluid leaked out of the lines it was done indiviusally,the system was completely bled as we flushed out the dot 4 for a dot 5 fluid and i was the one keeping the reservior topped up as the bleeding process was done my mechanic is stumped.Just got back from another guy who deals in BMW and he put on his code reader and reset the braking system no joy he's saying that the system has air and needs to be reverse bled.Never heard of that

 

Pretty short hard line between the right front caliper and the ABS. Not hard for me to believe that a bubble could slip up that to the ABS during a brake line swap there - ask me how I know... I lived with a soft pedal for a LONG time after my first line swap, until I finally did a full ABS power bleed with Autoenginuity - that fixed it.

 

DOT 4 is spec....
sometimes DOT 5 is incompatible with 4.....some 5's are silicone based...and require a brake overhaul to work correctly.Check the container.
If it is indeed compatible with DOT 4....then bleed away!!

 

do the dirt road bit . i had same issue and found a dirt parking lot and did like 10 stop and gos . if nothing else it'll get people really freaked out .

 

Ok,i've got the bottle here in front of me and it's Delphi Lockheed dot 5.1 and says it's a non silicone based brake fluid which exceeds F.M.V.S.S No116 DOT5.1,specification S.A.E. J1703 and can be mixed with all brake fluids metting the above spec.So this fluid should be fine.

 

I'll get to it this weekend and if solved i'll fill you guys in with what worked,in the meantime thank you for the feedback.Cheers Peter