[TohaFzv]

Hello everyone

I have a 2017 540xi (m sport brakes) and the car was recently due for a brake fluid flush. I went to my local bmw dealer to get it done and after picking up the car I noticed my brake pedal felt absolutely horrible.

Brakes used to be one of my favorite parts of this car. Now, the first 10-20% of the brake pedal travel pretty much does nothing and beyond that the brakes feel 30-50% less effective and softer than before. I can't judge the maximum performance of the brakes since I've never really pushed the pedal to the floor prior to getting the brake fluid changed.

I took the car back to the dealer next morning, they bled the brakes one more time and said that no air had come out. Several people at the dealership test drove the car and claim the brakes perform as they should.
Next I went to a reputable Indy bmw shop. They changed the brake fluid and bled the brakes twice. No improvement. They also tried to manually bleed the system by having a person press on the brakes, no air will come out and 0 improvement in brake pedal feel. The entire brake system has been inspected, no fluid leaks detected.

The tires, rotors and pads won't fix the issue. The tires are brand new Michelin's that were mounted a couple months ago and the brake rotors/pads have been checked and are in great shape. Furthermore, those aren't the variables that were changed since they are in the same condition as they were prior to brake fluid change.

I'm really not sure where to go from here, my next option is to have the master brake cylinder bench bled, however the shop owner who said that it's a 600$ job and in his opinion it's unlikely it'll fix the issue. The dealership simply offered me to trade the car in for a new one...

I will appreciate any suggestion, knowledge and experience you guys can share. I will also keep this thread updated so then hopefully once I fix the issue it'll be great source for everyone with similar issue.

[admranger]

Activate traction control and abs a couple times (find some loose dirt in a parking lot). Sometimes that will free up any air in the system. Re-bleed with a pressure bleeder.

[aerof16]

A bench bleed of the MC would be required if somehow BMW let the reservoir run dry while trying to bleed the brakes.

I don’t know what the problem is but I’d recommend you keep working with the BMW dealer you took it to originally. If they won’t fix it then get in contact with BMW USA or whoever.

If you tell them you had an Indy shop look at it, then the dealer is off the hook.

There is air in the system if the pedal is soft, just gotta figure it out.

I bled my brakes on my 2017 540i in my garage with a pressure bleeder and it’s as easy as it gets. M-sport brakes on my car too. They can put a pressure bleeder on the car (which is probably how they bleed the brakes at the dealer) and pressurize, then let it sit for a while and see if the pressure drops. If so, you’ve got a leak somewhere. If air or fluid can escape, then air can and will get in and your pedal will be soft. Won’t find the leak if you don’t pressurize the system though.

[G30 B58]

Originally Posted by aerof16

There is air in the system if the pedal is soft, just gotta figure it out.

[Chasta]

I assume air got into the ABS system. If so, a simple bleeding of each caliper will not be sufficient. Please update us when and if a solution is found.

[430Scud]

Originally Posted by admranger

Activate traction control and abs a couple times (find some loose dirt in a parking lot). Sometimes that will free up any air in the system. Re-bleed with a pressure bleeder.

Definitely worth a try. The factory method is to open up the ABS system valves using an appropriate scan tool during the bleeding process. If you don't you are leaving old fluid stuck in the system.

At a tech session at the local Ferrari dealer they showed bottles of brake fluid removed from cars. One had been serviced the previous 10 or 12 years at an independent shop that did not have the proper scan tool. When they performed a brake bleed, all the fluid that was trapped behind the ABS was contaminated with water and discolored. The rest was pretty clean and only a year or two old. They said one way to do it if you don't have the tool (wastes a lot of brake fluid) is to bleed the brakes. Go for a drive and activate the ABS several times, then go back and bleed again.

[430Scud]

Its also possible seals or something failed it the master cylinder/booster. I recall many years ago I was having a major service performed on an older Honda Accord at the dealer (timing belt, valve adjustment, all fluids and filters changed) and the master cylinder failed during the bleeding process and they had to replace it. Don't know if it was random failure or something they did, but it was a Honda, so not an expensive part or labor.

[TohaFzv]

Thanks for all your replies and suggestions. Updated as of right now:

- The dealership said they won't take any responsibility since the car has now been to Indy shops. Problem is that I tried working with them but they pretty much kicked me out of the dealership because they kept claiming the brakes work as they should while I kept saying they performed differently right before I dropped the car off for the fluid change. So in the end they said there's nothing else they can/are willing to do and I had no other choice other than going to an Indy shop

- I brought up my theory that there might be air in the abs system to the Indy shop but they said that though it could be the case for older bmw models such as e90 chassis, the way the brake system works on the g30 there's no way for air to be trapped in the abs system (would love to hear if someone can either approve or disprove this).

- To my thought that there might've been air trapped in the master cylinder, the shop said it's highly unluckily mainly because if there was air there would be inadequate pressure in the brake system and the sensors would've picked it up and thrown a code. Can anyone comment on this? Should there be any sensors right before or after the master brake cylinder?

- One of the shops I went to suggested that the brake pads can be glazed causing bad initial brake bite. I'm yet to try and change brake pads because I don't want to change any variables to try and isolate this bad pedal feel issue first. The brake pads aren't super worn out, they're within spec. And nothing changed since I dropped the car off about the brakes system other than the fluid flush. Though the shop suggested that the dealership could've somehow glazed the pads while test driving the car after the fluid flush.
To this pad glazing theory, I also feel like the pedal doesn't feel right even when the car is stationary. When I get in the car and put my foot on the brake to start it, the pedal hasn't been feeling right after the dealership flushed the fluid. Both before and after I start the engine.

Finally, I would like to ask you guys to share how your brake pedal feels:
1) When the car is stationary, Is the pedal very light? I'm able to press my down with very very light resistance and it's even resistance all the way down
2) While driving, first 10-15% of pedal travel, how much do the brakes bite? On my car (after the fluid flush) it feels like first 10-15% of brake travel give you 1-2% of brake engagement. I can hardly even tell if there's any brake engagement at all other than the brake lights coming on in the rear.
3) While stopping at the light or stop sign are the brakes so soft that the car is easy to stop without a "jerk" in the end? Before the brake fluid change I felt like the brakes were so grabby you had to try hard to stop smoothly. Now my g30 feels like a Lexus or an s-class brakes wise, it's now hard to make it jerk while stopping. It stops super smoothly, which doesn't feel right at all for a performance oriented car with optional sport brake system. This point kind of supports the theory of glazed brake pads but again the brake pad variable didn't change since this issue occurred unless they magically got glazed on a test drive.

I'm also curious if there are any g30 owners (ideally with m sport brakes) in the south eastern Wisconsin/north eastern Illinois that would be willing to meet and test drive my car? I'd be very curious to see if someone who's familiar with this car can confirm what I feel.

Thanks again for everyone taking their time to make suggestion. Truly appreciate it.

[Ninslothus]

Hey, I don't know if you've solved your problem by now but here is my take.
I had that issue on a couple VW Golf 6 I've been working on.
Solution was bleeding the breaks via the ABS module using ISTA/3rd party software, it will get the air within the ABS module out.
Also on some really hard cases taking off the calipers, blocking the brake piston and bleeding the brakes with the bleed valve on the topmost position while slightly moving the caliper (for some reason the bleed valve was lower than the pocket inside the caliper on this car)

Good luck!