I just got my 1-owner, 75k mile '03 MCS a few days ago. I'm getting used to its noises and behaviors, but a couple are standing out as odd.

When the car is running, there is a continual hissing that sounds like a vacuum leak coming from the pedal cluster area. Whenever I engage the brake or clutch, the hissing goes away and when I shut the car off, the hissing continues for about 10 seconds.

Has anyone seen this before? Normal, or something to investigate? I'm leaning towards investigate.

 

It could be a booster problem but that usually only happens when the brake pedal is depressed.

 

Yeah, I drove the car yesterday and paid particular attention to the noise. It does not happen with the clutch, it's brake-only.

The noise does not occur when the brake is depressed, but does when the brake is released -- BUT, I can make it go away by pulling up on the brake pedal with my foot. So, it's definitely some kind of vacuum issue having to do with the brake. Where do I start in tracking this one down, has anyone heard of this before?

 

It is probably your brake booster. Check the vacuum lines and gasket at the booster, including the seal at the master cylinder. If they are ok, and it doesn't look like your sucking brake fluid into the booster, start looking for a new booster.

 

Great news.

How involved is the booster replacement procedure? I'll start searching. Thanks!

Edit: I cannot find pricing or any other type of information on this. Can someone who has done this / had it done give me an idea of parts price? What labor hours does the dealer charge?

 

You'll have to remove the master cylinder, not sure if the lines will need to come off. there may be enough room to move it over. That will require removing the air box and the barrier behind it. Then you will need to remove the lower dash panel to get to the retaining nuts and pedal connections. The book say to remove the cowel panel and wipers (that would require the fender coming off), but that may not be needed. I have my car apart now and it looks like there may be enough room to get it out without doing that. If you have to disconnect the brake lines, it would be a good Idea to have the dealer bleed the brakes using a computer sequence, but make sure that actually use it.

You can also disconnect and plug the vacuum supply to the booster and make sure the noise is gone just to be sure.