weird braking issue

bleunetizen · 05-24-2018, 03:55 AM

Hi guys, just wondering if someone had a similar issue.

I sent my car in to have my front seat belts replaced because they became bit stiff to pull out.

On my way home after I got the car back, I noticed that my car was slowly creeping forward at a traffic light with my foot resting on the brake pedal, so I pressed it harder and the pedal sunk in further then it stopped the car from rolling.

It feels like as if there is some air trapped in the system, not sure why this happens after having the seat belts replaced - probably unrelated and just a coincidence.

The initial bite is fine when the car comes to a stop. But if I put even pressure on the pedal and keep it there for a second or two, the bite goes away and the car starts creeping forward/backward, then I press the brake harder and the pedal sinks like an inch or so without any resistance, then the brakes bite.

I can repeat this over and over, the initial stopping is always fine but the pressure goes away after a little while.

I am suspecting either some air got trapped in the brake lines somehow or my master cylinder is playing up a little.

I rang the service center and they had a quick look, and they are saying the car is 'within BMW's specification' so they cannot do too much about it unless they can prove something is actually wrong according to their books.

They told me to drive it for a day or two and see if it still feels weird, whats weird is how this started to happen after I got my seat belts replaced lol

Anyone?

M6 in Bama · 05-24-2018, 02:16 PM

Almost sounds like a vacuum leak, like the check valve between your booster and engine leaking a little.

bleunetizen · 05-29-2018, 07:07 AM

Haha this is going stupid now!

They had the car overnight to carry out some tests and are still saying that they cannot find what is causing the problem because all test procedures didn't show any problems, pretty much saying that I should just live with it.

They are saying that they will need to be able to prove the problem before they can claim it through the warranty process, which I can understand.

I asked if it is normal to have the pedal to sink when apply brakes then, and they are saying "I know what you are feeling and our techs felt it too but cannot find the fault".

Then I asked "it never did it before, it happened recently" and they go "errr but we could not find any fault".

They are saying that they can understand my problem but they cannot fix without replacing the entire brake system. Hell then they should just replace the entire system if they are recognizing the problem lol

Maybe I should take it to a different bmw dealer workshop?

bleunetizen · 05-29-2018, 09:14 PM

Looks like someone who is more technically inclined has tested the car out at last - and they finally admitted that the master cylinder is playing up. Instead of asking me to live with it, now they are suggesting that I should leave the car with them as it is unsafe to drive, until the new master cylinder arrives from Germany.

Looks like I will be missing my M6 for 3 or 4 weeks, time to clean up my garage I suppose lol

05-24-2018, 03:55 AM	#1
bleunetizen Private 12 Rep 60 Posts Drives: F13 M6 Join Date: Feb 2017 Location: New Zealand iTrader: (0)	weird braking issue Hi guys, just wondering if someone had a similar issue. I sent my car in to have my front seat belts replaced because they became bit stiff to pull out. On my way home after I got the car back, I noticed that my car was slowly creeping forward at a traffic light with my foot resting on the brake pedal, so I pressed it harder and the pedal sunk in further then it stopped the car from rolling. It feels like as if there is some air trapped in the system, not sure why this happens after having the seat belts replaced - probably unrelated and just a coincidence. The initial bite is fine when the car comes to a stop. But if I put even pressure on the pedal and keep it there for a second or two, the bite goes away and the car starts creeping forward/backward, then I press the brake harder and the pedal sinks like an inch or so without any resistance, then the brakes bite. I can repeat this over and over, the initial stopping is always fine but the pressure goes away after a little while. I am suspecting either some air got trapped in the brake lines somehow or my master cylinder is playing up a little. I rang the service center and they had a quick look, and they are saying the car is 'within BMW's specification' so they cannot do too much about it unless they can prove something is actually wrong according to their books. They told me to drive it for a day or two and see if it still feels weird, whats weird is how this started to happen after I got my seat belts replaced lol Anyone?
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05-24-2018, 02:16 PM	#2
M6 in Bama New Member 6 Rep 10 Posts Drives: 2014 M6 Vert, Saphire Black Join Date: May 2018 Location: Spanish Fort, AL iTrader: (0)	Almost sounds like a vacuum leak, like the check valve between your booster and engine leaking a little.
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05-29-2018, 07:07 AM	#3
bleunetizen Private 12 Rep 60 Posts Drives: F13 M6 Join Date: Feb 2017 Location: New Zealand iTrader: (0)	Haha this is going stupid now! They had the car overnight to carry out some tests and are still saying that they cannot find what is causing the problem because all test procedures didn't show any problems, pretty much saying that I should just live with it. They are saying that they will need to be able to prove the problem before they can claim it through the warranty process, which I can understand. I asked if it is normal to have the pedal to sink when apply brakes then, and they are saying "I know what you are feeling and our techs felt it too but cannot find the fault". Then I asked "it never did it before, it happened recently" and they go "errr but we could not find any fault". They are saying that they can understand my problem but they cannot fix without replacing the entire brake system. Hell then they should just replace the entire system if they are recognizing the problem lol Maybe I should take it to a different bmw dealer workshop?
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05-29-2018, 09:14 PM	#4
bleunetizen Private 12 Rep 60 Posts Drives: F13 M6 Join Date: Feb 2017 Location: New Zealand iTrader: (0)	Looks like someone who is more technically inclined has tested the car out at last - and they finally admitted that the master cylinder is playing up. Instead of asking me to live with it, now they are suggesting that I should leave the car with them as it is unsafe to drive, until the new master cylinder arrives from Germany. Looks like I will be missing my M6 for 3 or 4 weeks, time to clean up my garage I suppose lol
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