My brake pedal feels quite soft and tends to keep sinking if you hold your foot on it. I'm assuming it just needs a fluid change - not sure when last done by previous owner(s). My question is Volvo specify Dot4+ fluid for the vehicle. I have standard Dot 4 fluid already, so apart from having a slightly lower boiling point, is there any reason not to use it? Thanks.

Well I went ahead and changed the brake fluid today. I seem to have a problem though. After changing the fluid, I'm hearing a definite puff of air from the footwell when I apply the brake pedal - certainly cant recall having heard this before. I used a one man brake bleeding kit - the type with the one way valve on the end - and kept the fluid topped up throughout. I've done this numerous times on my previous cars without issue. Plenty of fluid came through, but the old stuff wanst particularly dark in colour. I guess I may have some other issue - maybe a seal in the brake servo? I'll have to do a search on the forum to see if this is a common issue, but any advice gratefully received.

hi tim..take a look at links below

Thanks for those links. I found a few others also (some on this forum), but they all seem to have the hissing sound continuously, or that it goes away when they apply slight pressure to the pedal. Mine isnt so much of a hiss as a real puff, and only when I press the brake pedal and having just looked on Vadis, it appears there is a rubber cover over the brake pushrod where it goes through the firewall (which look just like some bellows). I'm wondering if in bleeding, the pedal has gone down further than normal and the rubber 'bellows' are caught somehow, so that when I press the pedal they puff out air ?? Fingers crossed its something simple like this, I'll take a look tomorrow.

Well I've done a few more checks/tests today. Firstly, I followed the procedure to check servo and master cylinder - engine off, pump pedal to deplete vacuum, pedal gets very firm with minimal movement when pressure applied. Then started engine with foot applied to pedal, pedal gets lighter and drops slightly. This is as it supposedly should be - so appears to pass the basic tests. I also get no continuous hissing noise - simply a puff as the pedal is pressed. I then checked the rubber boot and pulled it back slightly so there was a definite air gap, with engine running tested again and 'puff' still sounded. From my understanding of the servo, when you apply the brakes you allow air into one side of the servo (the driver side) and this air at atmospheric pressure pushes the diaphram assisting with the braking effort. From what I can see this air enters at rear of the servo where it comes though the footwell and hence this is probably the noise? The only thing is I cant recall having heard it this loud before. If someone with a s60/v70 wouldn't mind applying the brakes with the engine running and with stereo turned down etc, could you tell me if you hear a 'puff' noise and if so how loud ?

I have a clear hiss and puff when pressing the brake, allways sounded like this. Would say its normal. - Johan S60 2,4T BSR St1. Polyflex front bushes.

Thanks Johan for confirming. I took the car out for a drive late last night, while the roads were quiet and the brakes seemed to be working ok.

Just for peace of mind, I asked a colleague at work with a 2002 S60 if he had this noise when pressing brake pedal - to which he said no. I asked if we could check in his car and with radio off and engine not running (vacuum still in servo) I pressed down on the pedal and heard exactly the same 'puff' sound. So I'm happy now that this is perfectly normal, but you just don't usually hear it or at least take notice of it. Thanks everyone for your input.