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Volvo V70 diesel - hiss - barney100

Got a hissing sound on occasions from the brakes which disappears when the pedal is applied...is this just the vacuum filling or something else?

Volvo V70 diesel - hiss - Roly93

Might be light rust on the discs clearing.

Volvo V70 diesel - hiss - bathtub tom

I'd say it needs further investigation. It could well be an air leak. It shouldn't affect the engine running, as it's a diesel. There's probably a mechanically operated pump somewhere creating the vacuum for the brake servo. Check the pipe, particularly at any connections (listen for a hiss with the engine running).

Does the servo maintain a vacuum overnight? Start the engine with your foot on the brake pedal, it shouldn't 'sink'.

Volvo V70 diesel - hiss - dereckr

I had something similar on the Xsara, also a diesel. It was some sort of air leak on the brake servo (mounted on the back of the braking master cylinder). It didn’t seem to affect brake assist, but I had it replaced. I advise that you get this checked out soon. I have since read about other makes of car suffering the same problem. The original servo was a Bosch, which is likely to be the standard fit on European built cars of this age.