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Hi All, I have been trying to replace my brake booster in my 2022 VW Passat AWM but have been having issues. The original brake booster failed due to water infiltration. Whenever it was freezing out, the water would freeze and prevent the brakes from working correctly. I replaced with a CARDONE 532947 remanufactured brake booster but am still continuing to have issues unrelated to the original problem. I have bled the brakes and done everything correct to the best of my knowledge. I get a hiss from the brake booster whenever I push down on the pedal. The engine stumbles and gives all indications of a vacuum leak. The brakes work but I need to push much harder than I should need too. Its obvious the booster is still not working as it should. I sprayed brake cleaner everywhere I could think of to test for a vacuum leak but I was unable to locate. Is it more likely the part is defective or am I missing a step in the process? Any suggestions or guidance would be appreciated.
 

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Discussion Starter · #3 ·
Defiintiely sounds like a vacuum leak. Also, guessing it’s a 2002. There is a big o-ring that goes between the booster and the master cycling der, could you have forgotten it?
Hi Hirnbeiss, Yes its a 2002. I have had it 21 years :). I replaced the o-ring on the master cylinder with a new o-ring that came from the kit. One question I had was where could the leak be if it only occurs when I depress the brake? For example if the leak was in the vacuum hose or check valve... then wouldn't the leak condition be present even when I don't depress the pedal?
 

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You can check that the booster is vacuum-tight using a mity-vac hand pump on the line going to the booster. I would do that first to rule that out.
There is a check valve also in the line to the manifold - did you disturb that during the R&R?
 

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Discussion Starter · #6 ·
You can check that the booster is vacuum-tight using a mity-vac hand pump on the line going to the booster. I would do that first to rule that out. There is a check valve also in the line to the manifold - did you disturb that during the R&R?
Hi Hierbeiss, yes, I vacuum tested this line today. Held 15 inhg for 5-10 min without dipping. Only when I hit the brake pedal did I loose vacuum. Based on what I think I know, that means booster diaphragm is only potental source of leak. Must be defective unit. Agree?
 

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Hi Hierbeiss, yes, I vacuum tested this line today. Held 15 inhg for 5-10 min without dipping. Only when I hit the brake pedal did I loose vacuum. Based on what I think I know, that means booster diaphragm is only potental source of leak. Must be defective unit. Agree?
This is a further indication of what I said in post #4.
 

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So if vacuum drops a lot when you depress the pedal, then it sounds faulty. If it’s only small bits of vacuum drop, it is probably working as it should, in which case your vacuum leak would be upstream of the booster.
 

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When the pedal is pushed the brake booster it should hold at least some vacuum. Vacuum will drop while pushing down on the pedal.
After the pedal is pushed down and held in that position, the vacuum should level off and hold there.
Double check the O-rings on both ends of the brake booster mounting surfaces to make sure they are sealing properly.

2 questions...

1) I gotta ask, are you sure you have the right booster?
There were multiple booster options for 1998 to 2005 model years.

2) By any chance does your car have the Brake Servo option?
If it does, it will have a silver canister type device located right next to the power steering reservoir.
Make sure you check ALL hoses going to the servo if you have one. Those hoses get hard and get hairline cracks in the end of the hose(s) and can leak.
There's also a check valve in one of the hoses going to the Brake Servo. Again, if you have that option.
 

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Discussion Starter · #14 ·
When the pedal is pushed the brake booster it should hold at least some vacuum. Vacuum will drop while pushing down on the pedal.
After the pedal is pushed down and held in that position, the vacuum should level off and hold there.
Double check the O-rings on both ends of the brake booster mounting surfaces to make sure they are sealing properly.

2 questions...

1) I gotta ask, are you sure you have the right booster?
There were multiple booster options for 1998 to 2005 model years.

2) By any chance does your car have the Brake Servo option?
If it does, it will have a silver canister type device located right next to the power steering reservoir.
Make sure you check ALL hoses going to the servo if you have one. Those hoses get hard and get hairline cracks in the end of the hose(s) and can leak.
There's also a check valve in one of the hoses going to the Brake Servo. Again, if you have that option.
Original part # = 8E0612105J

To the best of my knowledge its the right booster. Most parts suppliers list parts based on Make/Model/year/engine. How would I know?

I do have Brake Servo option but this was not the need for the replacement originally. Original booster had water infiltration. Line from Servo to booster has been tested and holds vacuum
 

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FYI, it is not an option. The brake servo was only standard on auto trans models.
 

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So if vacuum drops a lot when you depress the pedal, then it sounds faulty. If it’s only small bits of vacuum drop, it is probably working as it should, in which case your vacuum leak would be upstream of the booster.
This points to a faulty booster and you need to replace it. I can’t think of anything in installation that could cause this, unless you used a sledgehammer or drill in a bizarre customization of the bolt-in process ;).
 
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