Jump to content

Welcome to RennTech.org Community, Guest

There are many great features available to you once you register at RennTech.org
You are free to view posts here, but you must log in to reply to existing posts, or to start your own new topic. Like most online communities, there are costs involved to maintain a site like this - so we encourage our members to donate. All donations go to the costs operating and maintaining this site. We prefer that guests take part in our community and we offer a lot in return to those willing to join our corner of the Porsche world. This site is 99 percent member supported (less than 1 percent comes from advertising) - so please consider an annual donation to keep this site running.

Here are some of the features available - once you register at RennTech.org

  • View Classified Ads
  • DIY Tutorials
  • Porsche TSB Listings (limited)
  • VIN Decoder
  • Special Offers
  • OBD II P-Codes
  • Paint Codes
  • Registry
  • Videos System
  • View Reviews
  • and get rid of this welcome message

It takes just a few minutes to register, and it's FREE

Contributing Members also get these additional benefits:
(you become a Contributing Member by donating money to the operation of this site)

  • No ads - advertisements are removed
  • Access the Contributors Only Forum
  • Contributing Members Only Downloads
  • Send attachments with PMs
  • All image/file storage limits are substantially increased for all Contributing Members
  • Option Codes Lookup
  • VIN Option Lookups (limited)

Weird - Firm Brake Pedal before Start-up


Recommended Posts

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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 by the head
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.