07 xc90 brake booster issue

vmaxmike · Post by **vmaxmike** » 29 Jan 2014, 18:38

Hoping someone might know what's going on. My car had a small oil drip from the brake booster vacuum pump (common issue on these cars) which I finally fixed after first replacing the o-ring between pump and engine
(didn't stop leak) then later replacing the o-ring behind the outer cover of pump. This fixed leak but next morning there's NO brake boost anymore at very slow speeds!? Brakes are normal at driving speeds. There's only 1 moving part inside the pump and would seem impossible to fail. Should I replace pump or could booster have all of a sudden failed? Very strange...

Post by **jimmy57** » 29 Jan 2014, 19:23

Is the leak stopped?
The pump will not work if cover isn't sealed but it should leak oil, a lot of oil if that is the case.
You are right that there is not much inside pump. Only the rotor, the vanes, and a check valve. The check valve could be wedged open by something or the vanes may have broken. Th check valve is a reed style with a curved steel piece over it. The air drawn in by pump goes inside engine through that check valve. Without the check valve it makes vacuum pulses but not enough for brake booster to work.
You should hear hissing noise inside vehicle if the booster is not sealing for some sudden reason. I doubt that though. To be sure vacuum pump is dead you can remove check valve on booster, it pops out if you wiggle it arund while pulling outward. It is stuck into a grommet on booster housing.

vmaxmike · Post by **vmaxmike** » 30 Jan 2014, 05:59

Thanks for reply! Yes leak stopped and no hissing inside car. Strange part is brakes were fully functional when it was leaking. Car still has normal brake boost when driving she say over 10mph, but not when backing up or parking when RPM is very low. I'll look at that valve again but suspect the small amount of sealer I used on first attempts to fix leak from cover somehow messed things up

vmaxmike · Post by **vmaxmike** » 30 Jan 2014, 06:05

I want to remove hose from pump to feel suction level too but was unable to figure out how it comes off? Wasn't sure if you simply squeeze the plastic clamp thing and pull off or what? thanks

vmaxmike · Post by **vmaxmike** » 30 Jan 2014, 06:51

Someone suggested that by fixing a leak, the extra pressure can easily finish off an old booster. My thought is an '07 is not that old.