Hissing sound at the servo when releasing the pedal

[oragex]

I just went through this issue on my 2003. I will soon upload a DIY video on my channel with repairs https://www.youtube.com/playlist?lis...ECTts0FSVSOT_c .

The servo (brake booster) has a seal where the rod from the brake pedal goes into the booster. This seal is covered with a grey bellow. The seal needs lubricated with a special silicone grease that is applied on the white cylinder that is sliding on the seal. After several years, the special grease dries out, and the rubber is no longer lubricated. The rubber then gets torn and the brake booster starts loosing vacuum and will hiss when the brake pedal is released. Moreover, the brake booster electric vacuum pump can start running after the engine is shut off to compensate and the pump will wear after a while.

The faulty seal can be bought separately plus the white cylinder needs lubricated: don't use any silicone grease, many of the silicone greases on the market get stiffer in cold weather which will damage the seal. I will try the Volvo silicone grease for the caliper pins (part #1161688).

As for the seal, it's part # 03.7718-5018.1

URO has a kit https://vimeo.com/210329449 - Carefully with the white cylinder, it should not be scratched with the tools when replacing the seal

This is another brand https://picclick.co.uk/Brake-Booster...165600600.html
https://www.ebay.ie/itm/282046759411

There may be other brands out there.

The big problem is replacing the seal as this normally will require to remove the brake booster from the car. On the cars with right hand driving, this is terrible as the whole engine needs to be lowered several inches to clear the booster. Even on the cars with left hand driving this is not the easiest task.

I don't know if it's doable to replace the seal without removing the brake booster from the car. Not sure if someone already succeeded this way.

But at least if the booster is removed from the car, it doesn't have to be replaced, just the seal.

Also, even if the booster isn't hissing yet, I would recommend tossing the grey bellow, and applying a quality silicone grease on the white cylinder - again, the word quality is essential here as this may rather damage the seal instead of extending its life. Don't forget to place the grey bellow properly secured back in place to prevent any dirt from getting to the seal.

Hopefully this helps.

[Mac940]

It may not be too late to apply the grease even if it starts hissing. If the seal is not pulled out or cracked the grease will slightly expand the rubber and stop it leaking.
And yes it is possible to replace the seal without removing the servo!
I've done it on another car, you need to:
-disconnect the pin connecting the brake pedal
-pull the grey gaiter off
-pull out the old seal with claw like tool (or a bent wire etc)
-lubricate new seal and gradually push it in with something smooth without any rough edges. Other end of a thick makeup brush did it for me.
-put the gaiter back on
-put the brake pedal pin back through-i strongly advise to replace the clip for a new one-you don't want to lose your brakes if the old bent clip brakes!

There's very limited space and you'll end up scratching your hands laying on the floor with a cramp in your leg and you won't be able to move lol.
But it's much faster and simpler than dropping the engine

[reggit]

Hey this is great information as this is one of the jobs I need to do on the 'new' V70.

I'll be ordering the bits today if it's a reasonably easy DIY proposition.

Malc, what did you lube the seal with?

[Mac940]

It was a while ago.. 80% silicon grease but I'm really not sure. But I know for sure that it needs to be "rubber safe" grease as I read that some types can rapidly destroy the rubber.
Be aware that the job is very fiddly, uncomfortable and extra frustrating - one of the worst I've ever done on the s60 😁

PS. Now they're selling new seals on their own...
When I was doing the job none were available so I had to buy a used servo from a low mileage car, pull it apart and use the seal from it

[reggit]

Originally Posted by Mac940

It was a while ago.. 80% silicon grease but I'm really not sure. But I know for sure that it needs to be "rubber safe" grease as I read that some types can rapidly destroy the rubber.
Be aware that the job is very fiddly, uncomfortable and extra frustrating - one of the worst I've ever done on the s60 ��

Ta - it's either that or pay someone a lot of money! Got a big tub of rubber grease, guess that'll do the job.

[Mac940]

Originally Posted by reggit

Ta - it's either that or pay someone a lot of money! Got a big tub of rubber grease, guess that'll do the job.

Good luck! Let everyone know how you get on 👍I would upload some photos for guidance but I lost them a while ago

[oragex]

Originally Posted by reggit

Malc, what did you lube the seal with?

After dealing with several silicone brands by the past, all of them were getting sticky or viscous in colder weather. Then I went to Volvo and purchased their Silicone grease for calipers https://www.youtube.com/watch?v=n2IKibOdABk

Using a grease adapted for this seal is critical, if the grease gets viscous in colder weather, the seal will be damaged and teared up. This is in fact the reason why the seal gets torn. I would even ask Volvo if they have a specific grease for this application.