Brake booster shot?

Knuppel · 10-24-2021, 03:31 AM

So my wife’s car had sudden loss of brakes. Hard pedal, she could not stop the car. Luckily nothing happened and she managed to bring the car home in one piece. The car was complaining about brake fluid service for a while, but i did this in 2020 and forgot to reset the timer.

First stop, checked the brake fluid level which was fine. Then did the brake pedal test, it was not depressing when turning on the engine. I then looked if i could see any loose hoses. The rubber hose connection at the vacuum pump (nr 8) seemed somewhat loose. I put this down to the cold temperatures that we had last week. I disconnected the hose connection at the plastic wall (nr 10), before the check valve (nr 11), and was able to feel suction with my finger, not very much though.

Since the hose parts aren’t that expensive (vs the brake booster itself) i decided to replace them and see what happens, nrs 4, 8 and 11. Yesterday they came in and i replaced them (rubber o-ring being a PITA!). Managed to do it without disconnecting the DSC pump. I noticed the new check valve required less force to open when blowing in the hose. I also noticed there was more suction then before.

Expecting all or nothing, brakes or no brakes. The pedal still did not depress after turning on the engine. It does move down slowly, after 30 seconds or so. When pumping the pedal when the car is off, only at the first press of the pedal (i think) i hear air, hard to describe though, it’s the sound you hear when you use a hand pump and pump a good amount of air in an air mattress. Strangely though, the car does brake normal now. I can’t tell what the experience was before all this, since my wife drives it, but the pedal isn’t hard, and i don’t have to put force on it.

Is it possible that the brake booster is leaking somewhat, but still working? That the braking issue was due to the lack of vacuum which caused the already slightly failing check valve not to open anymore?

BMW E91 2007, N46B20 engine.

Welcome to NBA Jam · 10-24-2021, 08:30 AM

Could either be the brake booster or part 11. A slightly leaking booster could exhibit those symptoms.

Since your car experienced a hard brake pedal while driving, I would recommend replacing both. Definitely not something you want to experience a second time.

Knuppel · 10-24-2021, 09:01 AM

Problem was not fixed. Still hard brake pedal no brakes.
Will let somebody replace the brake booster, not keen on bleeding the brakes on the street.

charlie_m · 10-24-2021, 10:55 AM

Could also be the vacuum pump, it's evidently a common problem with the N46 engine. Especially if the hard pedal happens while driving (ie not enough vacuum), and not just at a cold start (ie, bleeds down overnight). Hopefully your mechanic will check the vacuum level before replacing the booster.

https://www.e90post.com/forums/showthread.php?t=669908

Knuppel · 10-28-2021, 02:27 AM

Quote:

Originally Posted by charlie_m

Could also be the vacuum pump, it's evidently a common problem with the N46 engine. Especially if the hard pedal happens while driving (ie not enough vacuum), and not just at a cold start (ie, bleeds down overnight). Hopefully your mechanic will check the vacuum level before replacing the booster.

https://www.e90post.com/forums/showthread.php?t=669908

I did feel proper suction when touching the hose with my finger.
My wife never had issues with hard pedal. It was just instant, this made me think the brake booster diaphragm must have cracked or something.

Knuppel · 10-29-2021, 12:56 PM

Replaced the brake booster today. Whilst bleeding the brakes with INPA i get ‘brake pedal not fully released’ error after the first press pedal and release. The bleeding procedure then stops. The car is on a slight slope on handbrake but surely this shouldn’t interfere? Is there some adjustment that needs to be done to the pedal? Help…

Knuppel · 11-06-2021, 04:59 AM

For future reference:
Could not finish the bleeding procedure because the new brake booster was slightly shorter than the original. There is a brake pedal sensor that can be adjusted. Once I did that the brake lights went off and I could finish the INPA bleeding procedure.

Unfortunately the brakes were still hard. Turned out the be the vacuumpump, had a gut feeling in the beginning about this, but since there was some vacuum i went on with the check valve and brake booster. The nipple on top of the vacuumpump was very loose, and the direction in which it pointed gave me more or less vacuum. So in the end there was not enough vacuum for the brake booster. Replaced the entire pump and brakes are working perfect now.

10-24-2021, 03:31 AM	#1
Knuppel Private 6 Rep 55 Posts Drives: E91 Join Date: Feb 2019 Location: Netherlands iTrader: (0)	Brake booster shot? So my wife’s car had sudden loss of brakes. Hard pedal, she could not stop the car. Luckily nothing happened and she managed to bring the car home in one piece. The car was complaining about brake fluid service for a while, but i did this in 2020 and forgot to reset the timer. First stop, checked the brake fluid level which was fine. Then did the brake pedal test, it was not depressing when turning on the engine. I then looked if i could see any loose hoses. The rubber hose connection at the vacuum pump (nr 8) seemed somewhat loose. I put this down to the cold temperatures that we had last week. I disconnected the hose connection at the plastic wall (nr 10), before the check valve (nr 11), and was able to feel suction with my finger, not very much though. Since the hose parts aren’t that expensive (vs the brake booster itself) i decided to replace them and see what happens, nrs 4, 8 and 11. Yesterday they came in and i replaced them (rubber o-ring being a PITA!). Managed to do it without disconnecting the DSC pump. I noticed the new check valve required less force to open when blowing in the hose. I also noticed there was more suction then before. Expecting all or nothing, brakes or no brakes. The pedal still did not depress after turning on the engine. It does move down slowly, after 30 seconds or so. When pumping the pedal when the car is off, only at the first press of the pedal (i think) i hear air, hard to describe though, it’s the sound you hear when you use a hand pump and pump a good amount of air in an air mattress. Strangely though, the car does brake normal now. I can’t tell what the experience was before all this, since my wife drives it, but the pedal isn’t hard, and i don’t have to put force on it. Is it possible that the brake booster is leaking somewhat, but still working? That the braking issue was due to the lack of vacuum which caused the already slightly failing check valve not to open anymore? BMW E91 2007, N46B20 engine. Attached Images Last edited by Knuppel; 10-24-2021 at 06:08 AM..
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10-24-2021, 08:30 AM	#2
Welcome to NBA Jam Is it the shoes!? 3884 Rep 5,112 Posts Drives: (Sold) 2011 E92 335i ZMP 6MT Join Date: Mar 2014 Location: USA iTrader: (1)	Could either be the brake booster or part 11. A slightly leaking booster could exhibit those symptoms. Since your car experienced a hard brake pedal while driving, I would recommend replacing both. Definitely not something you want to experience a second time.
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10-24-2021, 09:01 AM	#3
Knuppel Private 6 Rep 55 Posts Drives: E91 Join Date: Feb 2019 Location: Netherlands iTrader: (0)	Problem was not fixed. Still hard brake pedal no brakes. Will let somebody replace the brake booster, not keen on bleeding the brakes on the street.
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10-24-2021, 10:55 AM	#4
charlie_m Private First Class 76 Rep 169 Posts Drives: 2012 328ix Join Date: Jul 2021 Location: SC iTrader: (0)	Could also be the vacuum pump, it's evidently a common problem with the N46 engine. Especially if the hard pedal happens while driving (ie not enough vacuum), and not just at a cold start (ie, bleeds down overnight). Hopefully your mechanic will check the vacuum level before replacing the booster. https://www.e90post.com/forums/showthread.php?t=669908
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10-29-2021, 12:56 PM	#6
Knuppel Private 6 Rep 55 Posts Drives: E91 Join Date: Feb 2019 Location: Netherlands iTrader: (0)	Replaced the brake booster today. Whilst bleeding the brakes with INPA i get ‘brake pedal not fully released’ error after the first press pedal and release. The bleeding procedure then stops. The car is on a slight slope on handbrake but surely this shouldn’t interfere? Is there some adjustment that needs to be done to the pedal? Help…
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11-06-2021, 04:59 AM	#7
Knuppel Private 6 Rep 55 Posts Drives: E91 Join Date: Feb 2019 Location: Netherlands iTrader: (0)	For future reference: Could not finish the bleeding procedure because the new brake booster was slightly shorter than the original. There is a brake pedal sensor that can be adjusted. Once I did that the brake lights went off and I could finish the INPA bleeding procedure. Unfortunately the brakes were still hard. Turned out the be the vacuumpump, had a gut feeling in the beginning about this, but since there was some vacuum i went on with the check valve and brake booster. The nipple on top of the vacuumpump was very loose, and the direction in which it pointed gave me more or less vacuum. So in the end there was not enough vacuum for the brake booster. Replaced the entire pump and brakes are working perfect now.
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