On my 2002 M5 with the engine running, I can push hard on the brake pedal and it will sink almost to the floor. While driving I have to plan a head allowing extra distance for stopping. This is not 'the feel' that I had in the past.
I have searched and read many posts on this site and several other BMW sites along with general Google searches.
This is what I have done so far with out any success. I did a brake pad replacement along with a brake fluid flush. I have owned this car since new and the ABS/DSC system had not been flushed with new fluid. I procured both ISTA+ and INPA software to activate the ABS/DSC system. I was unable to fine a full, step by step procedure for dummies. Lacking such info, I poked around, activated various pumps and valves, pushed more brake fluid through the calipers (rr, lr, rf, lf). With the engine off, the brake pedal was good and hard. I start the engine and I could (with hard foot pressure) press the brake pedal almost to the floor. When I separated the brake boost vacuum hose, I could hear a good amount of air moving.
I bought a new master cylinder, did a bench bleed, and another master cylinder bleed once it was reinstalled into the car. Then more pressure bleeding and still the brakes feel lacking in bite. I took the car to a local foreign car shop that used Rheingold software to work the pump and bleed the system. There was no change in the pedal feel.
I even went so far to try a 'fix' that I read on a M3 board where you set the brake pedal to 80% depressed for twenty four hours to 'decompress' any air that might be captured in the fluid. This did not make any change.
I took the car out on the road and activated the DSC several times while making left, right turns and straight line stopping. I was able to lock up the brakes and it felt better somewhat. I did a final bleed but the again, with the engine on, the pedal still goes down a lot to the floor.
At this point I am at a total loss as to what to do next. I thought I addressed all of the possible causes, but there must be something else going on.
I am hoping someone on the site can shed some insight as to a fix for this problem.
A Huge Thanks In Advance. This is a great site!!!!!!
A couple of things come to mind.
First are the brake lines. They are rubber and as they age, they degrade. That allows them to flex. So before you get fluid to the calipers, the fluid first pushes the brake lines out before the fluid gets pushed where you want it to go. So get some steel braided lines. They have kits for our cars.
The other thing to check are the pads. Different pads can have different feel. What pads are you using? People here may have experience good or bad with the pads you are using.
Finally an old track trick. When you come in after a session, the brakes are obviously very hot. We would pull the wheels and just crack the bleeder for a split second. It seemed to help keep air out of the lines. I will let the engineers on here explain why!
One other thought. When you get ready to brake, give the pedal a quick medium tap, then immediately hit it normally. If the pedal firms up, you have air somewhere in the system and unlikely the ABS since that is closed off unless activated.
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Last edited by gsfent; 29th November 2018 at 02:15 AM.