2002 V40 Brake Booster Problem?

JV40

Hi all. Having a bit of a problem with my V40 brakes on cold start. When car has been sat for a few hours, I start it up and the brakes are like a sponge as if there is no pressure/vacuum in the system. After sitting there for a couple of minutes with the engine running the brakes return to normal operation and the car drives fine. It been like this everyday for a week or two and seemed to kick in with colder weather but that may just be coincidence. Initial thought is a booster fault but I'd be keen to know thoughts.
I have also noticed that the drive belt seems to be flapping when starting cold and car is put in reverse (auto). Doesnt seem to flap in neutral or forward gears. Sorry for my lack of mechanical knowledge but could the 2 be linked i.e. does the drive belt have anything to do with creating vacuum pressure in the brake booster? Thanks for any help

nickm

Sounds like a master cylinder issue.
The booster holds about 3 pumps when the engine is off.
Then the pedal should be rock hard. Hold the the pedal down like this and see if it goes slowly to the floor.
Start the engine with your foot on the brake and see if the pedal falls a little

Also check the front engine mount Next to the drive belt to they are hydraulic and can lose fluid.
And the belt tensioner

JV40

Thanks for that. I took a proper look today as have not had a chance in daylight, can't see any fluid leaks around the master or brake lines. I'll run the test you suggested in a bit but as it feels like a vacuum issue I checked along the vacuum hose and it looks like there is possibly a cap missing. Hard to explain so I've taken a picture and circled in red. The top plastic piece looks very shiny, is there meant to be some sort of cap/cover there?

nickm

Yes you have a problem there

JV40

Any idea what should be there? Is it something that I could replace just the missing part (probably used) or is it a case of replacing the whole line and it's incorporated components? Thanks

nickm

I'm not around my car ATM. Pretty sure there should be a hose not sure if a valve is missing. Other posters?

JV40

So, I feel pretty dumb - had a look and the part had come off and dropped down into the engine a bit - hence not noticing it before. I have clipped it back on...looks to have a sensor on it.

Still, the same problem with no power brake vacuum pressure for 1-2 mins after initial start up when cold. Just ran your test to see what the experience is and behaviour is exactly as you describe...about 3 pumps when engine is off then goes firm...switch engine on and the brake pedal drops slowly

JV40

Isolated to a broken booster vacuum switch. Requires replacement with part 30620958

Philia_Bear

Spongy brakes are never vac assist just a bad master cylinder or air in the system

Hard brakes are a bad booster or vac line

JV40

My use of the word spongy was probably off...its a word Ive always heard associated with all things 'brakes' when they dont feel right. 'Hard' would describe better.
I cant find them now but there were 2 threads on other sites where the switch had blown its top off like mine and flung the internal spring out...both just required replacement of the hose/switch. Had a retired mechanic friend look this morning and he agreed, said its the switch.. booster is fine as it works after a minute or 2. Heres a similar thread but not the ones I was looking for
http://www.matthewsvolvosite.com/forums/viewtopic.php?t=26723

JV40

Here ya go
http://volvoforums.com/forum/volvo-s40-11/any-clue-what-part-21712/