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  #1  
Old 02-03-2022, 02:01 PM
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Brakes failed, car rolled back dangerously

So, the brakes failed on me and car rolled back, pressing brake pedal all the way did not help. I bumped into 2 other cars behind which stopped the x5.

The brake pedal would intermittently soften over a few months back, but I had ignored it. The failure was like instant.

What could cause this? My techie says it's the brake master cylinder, but he seems to be using elimination method. He will probably say it's the booster thereafter.

Anyone experienced this?

2007 E70 3.0si

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  #2  
Old 02-03-2022, 05:15 PM
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Classic master cylinder failure mode, or a split/bad leak in two brake hoses.
How was the bi-annual brake flush done, if the pumping the pedal method was used, the seals in the m/c are probably shot. If the bi-annual flush was not done, probably the moisture has gotten to multible calipers and it is time to renew your brakes.

What is the mileage and weather like where SAV is operated, will help more with diagnostics.

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Old 02-03-2022, 05:16 PM
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Line failure? Something is preventing any pressure from being built up in both circuits though, so maybe it could be the master. I've had hard lines under the car (in an E53 corrode and eventually split under pressure, but unless a line in both circuits went at the same time, it seems unlikely you would loose any and all brake function..
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Old 02-03-2022, 06:01 PM
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Quote:
Originally Posted by wfwright2 View Post
Classic master cylinder failure mode, or a split/bad leak in two brake hoses.
ok....
Quote:
How was the bi-annual brake flush done, if the pumping the pedal method was used, the seals in the m/c are probably shot. If the bi-annual flush was not done, probably the moisture has gotten to multible calipers and it is time to renew your brakes.
I don't think I ever flushed the brake fluid in the last years. Would this cause such a catastrophic and sudden failure?
Quote:
What is the mileage and weather like where SAV is operated, will help more with diagnostics.
About 70,000miles. It's used in deep tropical Africa. Hot sun, occasional mud, plenty potholes, lots of dust.




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Old 02-03-2022, 06:43 PM
ard ard is offline
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lol..your brakes have been failing for months...yet you seem to insist this was 'sudden and totally unexpected'


Seriously....
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Old 02-03-2022, 09:19 PM
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Originally Posted by ard View Post
lol..your brakes have been failing for months...yet you seem to insist this was 'sudden and totally unexpected'


Seriously....


Every two years flush or else.
As Ard implied, your soft pedal during previous months told you something was wrong. Classic failed M/C.

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Old 02-03-2022, 10:12 PM
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Quote:
Originally Posted by wfwright2 View Post


Every two years flush or else.
You can go three years with this extended life Bosch product

https://www.amazon.com/gp/product/B07338GQM8
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Old 02-04-2022, 01:48 AM
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Quote:
Originally Posted by ard View Post
lol..your brakes have been failing for months...yet you seem to insist this was 'sudden and totally unexpected'


Seriously....
Yes, guilty as charged. I know I know....

The pedal was a little softer, just a little softer... and I ignored it. I just did not expect a sudden failure the way it happened.

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Old 02-04-2022, 01:49 AM
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Originally Posted by wfwright2 View Post


Every two years flush or else.
As Ard implied, your soft pedal during previous months told you something was wrong. Classic failed M/C.

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Yes thanks all. Hunting for one. Lesson learnt.

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  #10  
Old 02-04-2022, 05:09 PM
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Yes thanks all. Hunting for one. Lesson learnt.

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Master cylinder replaced. X5 back to life!!

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