Hi,

Has anyone else ever experienced a hissing noise coming from under the dashboard near the brake pedal? The timing of the sound is rather random and oddly it stops when I press the brake pedal and returns when I release the brake pedal.

Fortunately, there is no change in brake pedal feel or performance. My independent Volvo repair shop believes it is an HVAC control flap (which is vacuum actuated) which developed a leak. And when I press the brake pedal the vacuum draw of the brake booster overrides the vacuum in the HVAC system(?)

Other than the sound, no other symptoms.

Thanks

Bob
2003 V70 2.5T AWD, 105K miles

 

I have a 2001 with the same problem.

Were you able to get it fixed?

 

Yes,

I determined it was the little grey bellows where the brake booster comes through the firewall. I found an excellent post here two weeks ago with photos but, now I can't seem to locate it again. Here is a related post:
https://volvoforums.com/forum/volvo-...lerator-54988/

The brake pedal is connected to the brake booster by a gold anodized push rod. Where the push rod enters the brake booster, there is a little grey rubber bellows. It is the seal where this grey bellows connects to the brake booster - the seal has failed and permits a vacuum leak. If you put your finger on it while the car is making the hissing sound, you will hear the change in sound.

I was able to resolve it simply by gently rotating the bellows and pushing the leading edge gently back towards the brake booster. This appears to have re-sealed the bellows and hissing gone. If it returns, I would consider gently smearing a little RTV sealant around the edge to fix it. I like the $5 fix rather than replacing the entire booster at the dealer for $700++

Bob

 

Booster/servo leak, You cant buy the seal, under the grey bellows there is a rubber lip on the visible part of the seal that touches the metal surface of the servo and it degrades, then the seal moves,hence the leak.
I replaced my one from a scrap yard a year or so ago as Volvo wanted £400 and motor factor wanted £300.

I even used tiger seal around that part of the seal to give extra support,
But a week or two ago i heard the hiss.So looks like i will have to buy a new one next time.

ATE have superseding part numbers which suggest they are aware of the problem, the part number that was fitted to my car from the factory,ATE had no record of, the replacement had the same number, it looks like it was a duff batch of servos supplied to Volvo. ATE wont supply a seal so you cant rebuild it.

Done my one on the floor, two axle stands,and two jacks.
Bit of a pig to change as you have to drop the engine and box, and remember to disconnect all the wiring,steering and suspension links or you will bend something.that includes the steering column below the pedals.

Good luck

 

I had the seal leak vacuum, where the brake pedal pushes the plunger into the booster. Here is where my leak was. Underneath the gray bellows is a white ~2" diameter plunger that pushes into the booster.


The seal looks like this Mercedes ring seal

http://mbworld.org/forums/attachment...a-img_5014.jpg

but I could not find a Volvo replacement (which would take a half an hour to replace from the interior).


I got two quotes for over $700 to replace the entire brake booster assembly.

I cleaned the seal and with engine running and vacuum I applied a generous dab of Dow Corning 732 sealant to the ring seal, being careful not to get it on the plunger, then jiggled the piston to make sure the seal is seated and sealant filled the void. The sealant is a silicone paste that is very thick. It dries in an hour, cures in 24. I lubed the plunger and put the protective grey bellows back in place.

It has been over a month and NO LEAKS! Cost me less than $10!

 

Is this still holding up? I have 2008 3.2L V70 and am experiencing the same issue. Sound is very light, but thinking it will lead to a bigger issue.

Anyone have a write-up on how to replace on a 2008?

thanks!
Joe

 

The silicone patch job held up for about 6 months of constant use. It is now starting to hiss occasionally but not as bad as originally.
I have found a replacement seal kit available from URO PARTS in Simi Valley CA.
"Brake Booster Plunger Seal for Mercedes Volvo, URO Parts, 001 430 0708S"
It replaces ATE Brake Booster Plunger Seal 03.7718-5028.1 on Volvo & MB
Check around for prices
I have it but have not tried to replace it yet because they recommend removing the brake booster from the car to do it, and I'd like to try doing it underneath the dash while it is in place, by disconnecting the brake pedal and contorting myself into a pretzel. :-)
SEE VIDEO -https://www.youtube.com/watch?v=VheQtHwWO5s

 

Thanks for the quick reply!

I did some additional digging. Looks like the part# you provided is for V70's up to year 2007. Then they changed the brake booster in 2008.

Looks like a viable option though!. Back to the drawing board. May just have to replace the whole booster and do it right. I found Rock Auto has the best price @ ~236 for the whole booster including the 40 core charge

 

I fixed mine back in 2012, and its never leaked since.
see from my earlier post, that didnt work btw. replacing the booster, or servo as we like to call it in the UK, waste of time.

after fitting the second hand booster it had the same fault, in the end i disconected the brake pedal then carefully pulled the seal out from the booster from inside the car, then carefully cut away the failed part of the seal,(the rubber lip that runs the middle outside circumfrance of the seal with a pair of nail clippers, i know sounds mental ) re fit then used an appropriate o ring to fill the void of the part of the damaged seal i had cut away. I kept the original seal athough it had failed so i had a spare just in case i needed it, i will try and locate it and post a picture of my repair. it cost £7 (the cost of the 410 peice o ring set and took 20 mins to fix, my V70 is my daily drive still and is now 15 years old.