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Old 05-22-2018, 12:16 AM   #1
Edvis1599
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Brake booster leaks

Hello boys and girls!

So i have an issue. My brake booster is leaking somewhere... When car is running brake pedal is soft, booster is working. While car is off and brake pedal is hard, apllying pressure to brake pedal and starting the car releaves the pressure from the brake pedal, it goes down and gets soft.
But the thing is that when car sits not running for around 30-60mins brake pedal gets really really hard, barely pressable. So i assume that theres is a leak somewhere since it shouldnt get hard by itself, i mean it should hold vacuum for a press or two when the car is off.
I smoked my engine and theres no vacuum leaks, since i changed pretty much whole vacuum system. I havent done anything to my brakes. Smoked my engine from booster hose.

Sooo the question is, how can i determine where the booster is leaking? I heard that those booster leaks are pretty hard to determine.

Thanks for your answers mates!


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Old 05-22-2018, 12:40 AM   #2
jfoj
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Smoke testing a power brake booster can be difficult. The first problem is the plastic fitting on the brake booster is a one way check valve that will not let smoke into the power brake booster. Also some of the boosters do not leak as much when the brakes are not applied. Then you may have to get a good light up under the dash and have someone looking near the brake pushrod for leaks while someone else applies smoke to the power brake booster unless you have an automated smoke machine and a fitting for the brake booster that does not have a check valve inside.

https://forum.e46fanatics.com/showthread.php?t=1057387
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Old 05-22-2018, 02:29 AM   #3
Bidno
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Used section of hose with attached funnel to listen for, then locate/isolate vacuum leaks in engine compartment. Might help to locate while someone else works the brake. GL
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Old 05-22-2018, 07:10 AM   #4
jfoj
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Power brake booster will "leak" vacuum inside cabin. under dashboard.

One simple test is remove the power brake booster input check valve after engine has been off for 5 minutes or more and listen for the "whoosh" of air or release of vacuum. 30+ minutes is probably a better length of time for the test.

Power brake booster should hold vacuum overnight or longer without a problem.
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Old 05-22-2018, 07:48 AM   #5
MrMCar
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It's not uncommon for the booster to leak. We've taken apart the few we've replaced for a forensic inspection, with nothing remarkable found. Our evaluation is the diaphragm wears and leaks around the two studs inside and around the central shaft.

BEFORE you replace the booster, check for a vacuum line (E46 variant dependent) that resides just above the carpet line under the booster to the left of the gas pedal. We have seen a few of those (if equipped) leak and give rise to a false booster replacement diagnosis.

Another side effect of a booster leak is fuel trims fall out of tolerance and can/will set a check engine light.

Cars with the ABS/DSC unit on the right side have it easy, ones with the unit under the booster make replacement/bleeding more difficult.
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Old 06-30-2018, 02:28 PM   #6
TrentW
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Was ready to order a new booster this morning after having a situation yesterday where the pedal just lost firmness and went like 3/4 of the way to the floor.
Went out just now to see if I could determine a leak and...pedal is firm again and brakes seem to be working fine on a test drive.
Thinking I'll replace the check valve since it's easy and inexpensive. I'm not absolutely sure, but seems unlikely that the booster would leak one day and then not leak the next, and if it was the booster leaking, wouldn't the pedal go hard rather than soft and towards the floor?
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