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Brake Booster / Vacuum Pump - Functional Testing

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Brake Booster / Vacuum Pump - Functional Testing

Post by a3inverter » Mon Jul 09, 2018 8:54 am


I might be reading too many posts on this forum, but noted that I may have the brake booster seal issue yesterday morning. Power brake function is fine - stops the car nicely.

At rest (e.g. in the morning) if I press the brake pedal, I get a slight whoosh sound (same as the behavior on our Honda and my BMW) for a couple of pedal presses, then a hard pedal (again, same as our other vehicles). If the key is in Position II, I can hear the vacuum pump coming on for maybe 1-2 seconds. When running, there is no disruption idle when I press the brake. This morning 3 miles into my drive, I could still hear the pump coming on for that 1-2 second duration when I pressed the brake pedal but not after that. I have read here that the engine doesn't generate much vacuum until fully warmed up and that's the reason for the vacuum pump being on this car.

The URO replacement seal video that has been linked to by many has the whoosh sound when the brake pedal is RELEASED. I have it when it is DEPRESSED. I have yet to pull back the light gray perforated accordion seal to see if there are black marks on the white cylinder. There is some sort of lubricant/fluid that shows at the very end of the gray accordion.

Is there a standard/official test or set of diagnostic steps for this to determine if the booster is bad? The pump is definitely turning on so I don't believe that's the problem. I've seen a couple of different approaches honestly. I assume that I can pop out the check valve and verify operation by blowing into it in both directions with one direction passing air and the other not?

Relatedly, does anyone have a diagram of all the vacuum hoses on a 2.4 NA (2006 V70)? Wouldn't surprise me if some of those were brittle/cracked - I just want to make sure I get them all.


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Re: Brake Booster / Vacuum Pump - Functional Testing

Post by oragex » Mon Jul 09, 2018 9:53 am

Here's the vacuum lines near the throttle body on a 2003 na www.youtube.com/watch?v=aRGn6d2iAGE

Maybe also check the hoses around the vacuum pump switch (the thing attached to the air filter box). Also check this switch, the plastic cap can sometimes break off.

If you always have the brake pedal somehow 'soft' in the morning before starting the car, even after parking the car for a few days, I would worry about the seal - but it's very wise to lube it by now like in the video even if it appears to already have some greae on it - this grease goes bad with time.

When the grey boot is not attached, we can hear the whoosh louder, I wouldn't worry about this.
2003 2.4i S60 automatic 125k miles
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