I have this XC90 that has been sitting for a couple of years and still has no major issues, except the brakes are dragging, mostly the fronts. Also add to this, the booster vacuum pump keeps going off by itself and for that I suspect the booster check valve. Can the 2 be related? The brake drag seems to be worse at high speeds, also it seems to be dragging less when the weather is better. Calipers have been taken apart and lubricated, so that most likely is not the issue. Please help! Again: has anyone ever heard of the booster check valve causing brake drag? Is it possible?

Ps: I am not very mechanically inclined or experienced. I am aware of the many guides on how to test the booster, check valve, etc., just wanna know if this could be related! Thanks.

 

how does the brake pedal feel when you press it down during driving? Any odd sounds (ie hissing?)

 

I just checked, the brake pedal is hissing upon release.