Brake Booster Problem?

[sandytrean]

I think I have a bad brake booster, but I want to confirm before I burn a few hours doing the replacement job.

I get a hiss when I press on the brake pedal. I'll upload a video of the sound in the morning.

I also am able to pump the brakes up a bit when stopping. Its very slight. I'm replacing pads and rotors soon, so I'm hoping that will fix it, along with a flush.

Is my hiss from the brake booster, or just the check valve/vacuum leak. I have a booster from the junk yard, but I really don't want to install the thing just to find out it isn't good. Is it possible to test a booster when it is off the car?

[scot850]

Check for leaks in the pipe to the servo from the engine. The pipe can become crumbly with age.

The issue you are talking about could well be the check valve leaking which they can do as they get older. Part # for the replacement check valve kit for 95-97 850 is : 271632

Part is around $40 US on various on-line Volvo dealers.

Option is to pull one from a junkyard and hope it is ok.

I'd do these 2 things first before spending money on a booster and all the work involved with that.

Finally check the brake fluid level. Are you losing any fluid? The brake master cylinders leak into the booster and you may not see a leak.

Neil.

[sandytrean]

Is there a way I can diagnose the problem to the check valve?