andrewm 236 Report post Posted May 3, 2015 (edited) My 540i has always had spongy brakes, I bled it when I bought it but no dice. I assumed it had crap pads but one day my right front hose blew out and I wonder if it was just expanding this hose as it was weak (damaged), I replaced all with stainless lines and bled, better but still crap. I just put hawk hps pads in and bled 1L of BNT RBF600? (higher temp stuff) fluid through and its no better. However curiously on less warm mornings (less than 10C) I have perfect brakes, and this doesnt seem to change as I use the brakes which leads me to believe it is an issue with something not directly affected by brake temperature but by air temp. Current theories of mine, bad wheel bearing, bad master cylinder, air in DSC/ABS, and issue with right front caliper Current symptoms are spongy brake pedal like air in lines when air temp above 10C, squeak from right front caliper when braking and cornering tightly, same right front caliper has slight play as if guide pins were loose but they are definately not, same caliper outside pad is not making full contact with rotor (20mm rust ring on outside of rotor, have bedded properly and run these pads for 1500km) I have ordered guide pins, guide pin bushes and piston seal and dustboot for right front caliper and piston seal and dust boots for the other 3 calipers, I have also ordered a new master cylinder. Will update when I resolve this issue but in the interests of all the threads that helped me I thought I would start this one and resolve it, and actually reply with the solution. EDIT: have checked for leaks and no none are present, after two weeks level had not moved in brake master cylinder reservoir. EDIT 2: rebuilt the caliper that had play with new seal, new dustboot, new guide pins and new guide pin bushes. Piston was in near perfect nick, just some tiny rust colour staining that rubbed off and it looked brand new. Bled that caliper and brakes are not any better. Edited May 11, 2015 by andrewm Quote Share this post Link to post Share on other sites
M5V8 337 Report post Posted May 3, 2015 from reading I'd say you are on the right track. I'd pick either a old line or a master cylinder issue. Everything else is steel lines. Quote Share this post Link to post Share on other sites
