Brake booster hissing gently

[IdahoDoug]

Noticed near the end of our trip to Glacier in the quiet of a night time drive that the brake booster has begun hissing quietly. Its noticeable at a stop and quits immediately when I let off the brake pedal. In my research, I found mention of an O ring between the booster and the master cylinder as a possible source. Is that right - is there vacuum that O ring is sealing? It would be an easier fix than pulling the entire booster, but I don't want to mess with it if that is a false suggestion. I would not think there would be vacuum there, but will check the Bentley tonight to see what I can discern. Anyone know the scoop?

TIA, Doug
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1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[rubbachicken]

spray wd40 around the master cylinder joint, and the vacuum line to the inlet manifold, it'll temporarily stop the hissing if that the problem.
time to start looking for the BMW booster
_________________
lucy our westy

lucy's BIG adventure

meet 'burni'


markswagen {mobile mechanic} san diego area all early VW's cared for.

619 201 0310 or 617 935 4182

[90Doka_Guy]

Yup, I had the same problem although when mine was hissing the brake pedal position had no influence on it. A new o-ring stopped the hissing. I dropped a couple drops of soapy water on the joint before hand to confirm that it was the joint and not the booster. The bubbling was the smoking gun.
_________________
-'87 Westy
-'90 Tintop
-'90 DOKA

[IdahoDoug]

Great idea on the soapy water. As for a booster, the remarkable Van has several times demonstrated its ability to "find" things I need as it breaks itself. Meaning, I will discover I need a lower grille and next time I am at the U pull the stripped Vanagon will suddenly have one laying in the back seat. This time, we came back with the hissing on Monday and Tuesday I stopped by a place with a stripped Vanagon and the booster was still in it. Interior is bare metal, mind you - even the wiring harness is gone. So, I have a spare sitting in the garage mere hours from discovering the need. Apparently, I am just a pawn in Mango's life - destined to be sent off to locate parts and install them for her in a cruel cycle forever..... In fact, lately she has been encouraging me to purchase the half disassembled engine and trans, which I will surely do next week.

DougM
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[rubbachicken]

doug, are you auto or 4 speed.

if it's 4 speed, take out and inspect the clutch pedal, where the clevis pin is, 99% of the one's i've looked at the hole is worn to a slot, giving unwanted play at the pedal.
it'll need welding and redrilling if badly worn.

and regreasing when it goes back together
_________________
lucy our westy

lucy's BIG adventure

meet 'burni'


markswagen {mobile mechanic} san diego area all early VW's cared for.

619 201 0310 or 617 935 4182

[IdahoDoug]

So, bringing this back up as I'm going to see if anyone knows how to fix it. I see Van Cafe has a couple O rings for the brake booster. Anyone know where the vacuum leak is likely to be on the Vanagon unit? And what part I should have on hand before digging in?

With O rings I tend to want them in hand as they're cheap. Bummer to have it apart and discover it's just an O ring and wait a week to get one.

So I guess that's my question. What have people found to fix a booster that gently hisses when your foot is on the brake?
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[61Scout]

On a brake booster you've got atmospheric pressure on one side and an induced vacuum on the other. Then a return spring inside to stabilize the diaphragm. So the only things I can imagine would be leaking would be 1) the o-ring, 2) the connection of the vacuum line, or 3) a failed diaphragm. The first two would be fixed pretty easily, the last item would require booster replacement. In terms of parts handy, I think the o-ring is about the only thing you'll need to order. If it's the line connection, you'll have to determine if the hose is not making a good seal (dried out, cracked), or if the connection to the booster itself is cracked or compromised in some way. Still, if that were the case you'd think the noise would be constant in both of those cases.

Does the van loose vacuum on the booster overnight? A good booster will hold vacuum overnight easily. So if you have non boosted brakes first thing in the morning (without starting the engine) you've got a leak somewhere. If you have one last boost, and then on the next pump you have manual brakes, the booster is holding. It can of course, be checked with a pump and gauge too. But it would seem to me that if the problem only exists while you have your foot on the brake, the diaphragm may be moving/flexed to a point where it leaks, and then when you release your foot it seals up again. How bad of a noise are we talking about here? Do you have a video handy? Maybe I have something wrong here too... it's been a while since I've looked at any internals of a brake booster.

-Kevin
_________________
1986 Westfalia Weekender Wolfsburg, RJE 2.3
1985 Tin Top, Subie 2.2 + 5MT
Floppy Mirrors no more: http://www.thesamba.com/vw/forum/viewtopic.php?t=653018&highlight=
Remove the front spindle nut with ease: https://www.thesamba.com/vw/forum/viewtopic.php?t=679567&highlight=
Remove the rear wheel bearing housing without messing with the big 46mm nut: https://www.thesamba.com/vw/forum/viewtopic.php?t=679507&highlight=

-Nec Spe, Nec Metu

[IdahoDoug]

Nice explanation. So does anyone know what O ring I should have on hand? If I open things up and its the vacuum lines I can source that locally in a few minutes time. But I'd like to have the O ring on hand. Van Cafe has an O ring for the booster, but they're unclear what it is and where it goes. I'd hate to open it up and find the O ring is for a brake fluid leak or something..
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[61Scout]

Doug, looks to me like you need 357.611.243

I can get you a rough measurement tomorrow if that helps. I'm sure I have a master cylinder lying around in my recycle pile. There are no other seals to worry about as far as vacuum leaks.

Kevin
_________________
1986 Westfalia Weekender Wolfsburg, RJE 2.3
1985 Tin Top, Subie 2.2 + 5MT
Floppy Mirrors no more: http://www.thesamba.com/vw/forum/viewtopic.php?t=653018&highlight=
Remove the front spindle nut with ease: https://www.thesamba.com/vw/forum/viewtopic.php?t=679567&highlight=
Remove the rear wheel bearing housing without messing with the big 46mm nut: https://www.thesamba.com/vw/forum/viewtopic.php?t=679507&highlight=

-Nec Spe, Nec Metu

[alaskadan]

I had a vacuum leak there last year that resulted in a fading brake pedal. Turns out that rust had worked its way under the paint and behind the o ring. After sanding and repainting the area the original o ring was fine for re use.

[IdahoDoug]

Thanks guys. On my shopping cart now..
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[IdahoDoug]

OK, tackling this soon. Dash is out for the heater blower replacement, the awesome Jeep resister change (thanks, Dhaaver!), new foam on the air plenum doors, and the brake booster O ring is staring me in the face. Where is the O ring? My Bentley is at the mechanics in case he needs a spec while putting new bearings in my short block.

So is the O ring between the master cylinder and the brake booster? I think so, but need to confirm before taking things apart and screwing things up (that may happen anyhow, but why tempt fate, eh?).

Doug
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[IdahoDoug]

Help a brother out here. I've about got things ready to put the dash back in, have the O ring in my hand and don't have the Bentley. Is this between the master cylinder and the booster?

Thanks!
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[61Scout]

[IdahoDoug]

Excellent - thanks much. Will get to that this evening I think.

Doug
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[IdahoDoug]

So, in the quiet of the garage I was able to learn more about this. With my mity mac vacuum pump on it at 15, it sits there holding vacuum nicely. When I push on the brake pedal there is a hiss in the booster. As in inside the booster - not external like the O ring venting.

So, when sitting at a traffic light with my foot on the brake, I can hear the constant quiet hissing. Can anyone diagnose? Is that indicative of an internal booster problem, or just that I have good hearing.

It has been some time since I drove this girl (over a year) so I don't remember the brakes being problematic, though I have a vague sense that they initially brake well, but after a few seconds of braking I have to apply more foot pressure.

What do you folks think?
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[alaskadan]

Kinda sounds like it. When mine started leaking it was something that occurred over a month and a half or so. Starting with barely notable pedal fade to having to pump the pedal once in the middle of one of our steep hills in the final week prior to addressing the problem. I never heard hissing, and im pretty good at hearing new noises.

[61Scout]

I would also test on the other end of the line, the one originating in the engine bay. Does it still hold vacuum?

Also, how much vacuum was your original engine creating? And how fast was it creating it? Is this memory from before you rebuilt the engine? My thought is that if the engine was tired it may have taken a few seconds for it to build vacuum in that long line and to get the diaphragm ready. This would also help explain the pedal feel.

As for the noise inside the booster. It would be nice to find a cut-away or if someone has had one of these vanagon boosters opened. But it would seem to me like there has to be some kind of valving inside the booster. Yes, the return spring moves the diaphragm back towards the center/neutral position. But how does the air inside equalize?

My ears are not the best, but I checked a few of my rigs today and they all have some associated noise. To me, it sounds like air being regulated. Is it possible to get a video of this noise from the van?

-Kevin
_________________
1986 Westfalia Weekender Wolfsburg, RJE 2.3
1985 Tin Top, Subie 2.2 + 5MT
Floppy Mirrors no more: http://www.thesamba.com/vw/forum/viewtopic.php?t=653018&highlight=
Remove the front spindle nut with ease: https://www.thesamba.com/vw/forum/viewtopic.php?t=679567&highlight=
Remove the rear wheel bearing housing without messing with the big 46mm nut: https://www.thesamba.com/vw/forum/viewtopic.php?t=679507&highlight=

-Nec Spe, Nec Metu

[IdahoDoug]

Good questions. So I gathered some additional information and I also pulled the booster off my parts van for comparison. Heres what I found.

First, the vacuum line seems fine - holds vacuum. I can't speak for the other engine but I like your thoughts on that area. I got my Mityvac out and here's what I found.

My booster: Holds 15 just fine for hours. When I push on the pedal and hold it down, I can hear an initial whoosh and then it continues to slightly hiss and dies off as thought it is fully emptying the vacuum from my Mityvac. The guage drops to zero to confirm that - whether I hold it down or let it off.

Spare booster: Holds 15 just fine for hours. When I push on the pedal and hold it down, I can hear the same initial whoosh and then nothing. The guage drops to about 5 and stays there whether I continue holding the pedal down or let it up. If I push again, it drains the remaining vacuum.

So, I think something's wrong with my booster. I think the hiss of holding the pedal down like you would at a stop light is what I've been hearing when I last drove it and became concerned about the hiss. I agree I'd like to know what's in there and did some snooping around online to no avail. It seems really simple. Some have speculated this behavior means there is a leak in the membrane/diaphragm. I thought that did not make sense as I'd think the diaphragm would be constantly leaking and hissing. But it may make sense if there is no vacuum into the booster until the moment the brake is applied and then a valve opens to "admit vacuum" when you push the brake down. I think that's what is supposed to happen. So, not sure of the mechanics of what I think is a problem with that booster.

However, my plan is to use the spare booster with a new master cylinder and new seal between it and the booster. I ordered the new MC a few minutes ago from Van Cafe. They have a MC that is cheaper than Rock Auto, by the way. I am impressed at that value. NAPA was also way above it. Of course I had to get a few other things - braided brake lines, spare key blank, brake pedal pad cover.

So, anyone have a good explanation for the tribe on why this behavior happens? I can do some further testing if it helps, though understand my engine is not in the old girl at the moment....
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader

[Pottsalot]