Weird - Firm Brake Pedal before Start-up

[spooltime]

I've noticed recently that more often than not, when I first attempt to depress the brake pedal in order to start my Cayenne, the pedal caanot be pushed in at all.  Then, once it starts, the pedal depresses normally.  In the past, I could depress the brake pedal downward prior to starting.

 

I'm thinking the reluctant brake pedal when the engine isn't running is symptom of some problem with maybe the master cylinder or other hydraulic component, or perhaps a brake line.  I have no clue.

 

Anyone else encountered this or have any ideas on what's up with the no-movement brake pedal prior to start-up?

[plima]

It is possibly the vacuum booster leaking down.  Normally, the vacuum holds for days after running.  When there is vacuum, the pedal feels normal, but if there is no vacuum, the pedal will be very hard.  The brakes still are working, but there is no assist until the engine is running and vacuum is restored.  It that is the case, it isn't an urgent issue, but I'd still get it fixed, since if it were to get worse, it might reduce or eliminate the power assist to the brakes.

[spooltime]

Checked the parts diagram and it looks like there are two primary vacumn hoses and the pump itself.  I'm wondering if there's a way to isolate the vacumn leak to either the pump or one of the lines?  Since the system obviously re-pressurizes after the pump is running again, I'm wondering if the leak is in one of the lines or maybe a seal inside the pump?  Is R&R a DIY project or is this one for the dealer?

[the head]

Most likely the hoses by the electric pump are cracked.  Not enough to give you the brake warning light/message yet.  Take off the engine bay covers on the right side and start it up and listen for leaks.  You may also be able to find it once the engine is cut off and hear the air rushing in where the crack is located.  I bought silicone vacuum hose and just replaced the hard plastic lines.  They broke in 3 different spots before I finally had enough.  The symptom you describe is what happened in each instance, at least in my cases.

Edited June 28, 2014 by the head