I am looking for some guidance on what might be going on with my 09 C2 brake system. I've noticed recently that if my car sits for 24+ hours, the brake pedal gets really stiff. Once the car is started the pedal feels normal and I cannot detect any difference in pedal feel while driving. If my car sits for just a few hours then there is no change in the pedal stiffness.

I believe I have a vacuum leak either in my vacuum pump or possibly something wrong with my master cylinder? I'm not sure how to troubleshoot this issue and would appreciate any input/advice.

 

this is how my car is from day 1

 

I have the same issue but mine takes 2 to 3 days. It's just vacuum leaking from the vacuum assist can behind the master cylinder as you guessed. I am not worried about it as a minor leak will not affect braking performance during normal use. There is a check valve on it somewhere you could replace if you really wanted to, but I'm not going to mess with mine unless it gets a lot worse. My mechanic just serviced my brakes and I asked him about it and he also said not to worry unless it gets bad. I also have the 2009. Mine is a C4S.

 

pretty sure that's normal behavior...

 

My 2011 started doing the same a few months ago. I have a valved TopGear exhaust system. When I start the car after sitting for a few hours, the brake pedal is hard and the valves, in the exhaust, open for a few seconds until the vacuum builds up, about the same time the brake pedal softens. It has a nice growl with the cold starts, but I want to find out where the vacuum leak is.

 

Interesting. I don't have valved exhaust, but what you're saying makes sense if it's tied into the vacuum flow.

I am struggling to understand this being normal behavior, though. I've owned my car for years and it only started doing this recently. This leads me to believe something changed, but what? This thread has given me some reassurance that this behavior might be quite common though, and not lead to eventual brake failure or something.

As far as troubleshooting where the leak is, I am not sure how to proceed. For a crankcase vacuum leak a simple smoke test works, but this loss of vacuum isn't coming from the crankcase (I believe this to be true because if you pull your oil cap there is no impact on your brake pedal), it's something between the pump and brake system.

 

If you're worried about it you could smoke test at the brake booster but it's fairly normal for cars to do this when off. With PSE and the slight vacuum delay you now get that louder bark on cold start for a little longer = bonus

 

Don't confuse crankcase vacuum with brake system vacuum. Your 997.2 has a vacuum pump driven by the right side camshaft to provide brake vacuum.

 

Could be the brake booster. Had the exact same symptoms on my other car (IS F). Got progressively worse over about two years. Tried replacing the check valve first since much cheaper but no difference. Replacing the booster finally fixed it.