My 2018 R56S 6-speed auto has developed an issue that has become more and more prevalent over the last 3 months or so. When it happens, the brake pedal is hard to push far enough to let the starter toggle actuate the starter. Normal travel feels like about 1 to 1.5 inches. When this happens, it may move 1/4-1/2 inch, and has to be pushed pretty hard to start the car. It did not have this issue for the first 6 months I owned it. The brake pedal is very stiff after sitting overnight, sometimes after the 10 hours I am at work. When this issue started, it would take 2 or 3 days to manifest itself. The brake booster seems to be losing vacuum when it sits with engine off. I do not hear any vacuum leaks (like the "whooshing" sound I have heard while pressing the brake pedal when a vacuum booster fails), and it seems to operate fine while driving, with full power assist and no odd noises or anything. It is now at the dealer (MINI of Escondido) and they say they are unable to duplicate the problem, all feels fine to them. I have been a professional automotive mechanic/technician for over 30 years now, so I am familiar with brake booster bleed-down issues. Anyone have a similar problem? Anyone know if there is a vacuum check valve, and if so, it's location? I have a feeling I might be diagnosing and fixing this problem myself, despite the CPO warranty remaining in effect til April 2023. Thanks in advance for any shared experience/help/advice you can give.

Chris

 

Sounds like you have air in the ABS pump.

https://www.minif56.com/threads/f56-...g-issue.88264/

Have you flushed the brake fluid in your 4 year old car? You should do that at least once every 2 years.

 

I have not yet flushed the brake fluid, although I plan to once I get this situation sorted. As far as I know, there has been no brake work done, definitely none done since I bought the car almost a year and 10k miles ago. The brakes work perfectly once the car starts, it's just hard to press the brake pedal far enough to allow the engine to start after it sits for a few hours. I can replicate the same exact pedal feel by pumping the brake pedal 3 or 4 times once I shut the engine off, which expends the vacuum in the brake booster. This is why I think the brake booster is bleeding down through the vacuum check valve, which BMW calls a "non-return valve". The part is available, so if the dealership continues to insist that they cannot find the problem, or it's "normal", I will just buy it and replace it myself.

 

Hi Chris,
Did you manage to find a solution to your problem? My wife's 2015 manual Mini Cooper is having the exactly same issue. It seems to happen when the car is hot - not necessarily from driving but when it's sat out in the sun.
Any advice would be greatly appreciated! Our local garage thinks the clutch might need replacing, but it's only done 37000 miles so I've got my doubts about that.
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