Sinking Brake Pedal

[carvalag]

:huh:

Last weekend I was supposed to enjoy three fun days on the track. I got my CPO 06 997 C4 coupe with manual transmission prepared by installing yellow pagid brake pads and flushing the brake system (I used ATE TYP200). The brake pedal felt mushy after that. I bled the brakes again, the pedal got firmer, but I started to notice that the brake pedal would sink to the floor if I held it pressed for a few seconds. Suspecting of a problem with the master cylinder (MC), I brought my car to the dealer for an inspection and possible replacement of the MC under warranty. The dealer flushed the brake system one more time, this time with ATE Super Blue (which as I understand is the same thing as the TYP200 but blue instead of gold) and bled the ABS. This time around the pedal felt much firmer and wouldn't sink, so I drove 5 hours all the way up to the track site. In the last toll booth on my way, though, I noticed that the sinking pedal came back. By then, the nearest dealer was 100 mi away, and no dealer in a 300 mi radius had an MC in stock anyway so I decided to swallow my disappointment and drive back home, leaving my plans of track fun behind me. I got my car back to the dealer and they're currently replacing the MC. I'll let you know later whether this will solve the problem or not. I'm not particularly optimistic, though, because the dealer gave me a brand new (1,300 mi) loaner Cayenne to use while they fix my car and, guess what, the Cayenne's brake pedal sinks exactly like my car's! I did a search on web forums and found other people who noticed the same thing, including in brand new cars still sitting at the dealer's parking lot (check http://forums.rennlist.com/rennforums/997-...th-brakes.html).

I think a sinking brake pedal is tricky to notice because the pedal feels firm at first, and under normal driving the car brakes just fine. You'll only notice a problem if you deliberately keep pressing the pedal after you come to a stop, which I only did after I first flushed the system and was testing for potential problems. I think this problem may go unnoticed for months if you're not paying special attention to your brakes.

Do you test your brakes regularly for a sinking pedal? Is this a cronic problem with some of the newer models, or just "normal"? If "normal", how low can you (or the brake pedal...) go???

Edited August 3, 2009 by carvalag

[dphatch]

:huh:

Last weekend I was supposed to enjoy three fun days on the track. I got my CPO 06 997 C4 coupe with manual transmission prepared by installing yellow pagid brake pads and flushing the brake system (I used ATE TYP200). The brake pedal felt mushy after that. I bled the brakes again, the pedal got firmer, but I started to notice that the brake pedal would sink to the floor if I held it pressed for a few seconds. Suspecting of a problem with the master cylinder (MC), I brought my car to the dealer for an inspection and possible replacement of the MC under warranty. The dealer flushed the brake system one more time, this time with ATE Super Blue (which as I understand is the same thing as the TYP200 but blue instead of gold) and bled the ABS. This time around the pedal felt much firmer and wouldn't sink, so I drove 5 hours all the way up to the track site. In the last toll booth on my way, though, I noticed that the sinking pedal came back. By then, the nearest dealer was 100 mi away, and no dealer in a 300 mi radius had an MC in stock anyway so I decided to swallow my disappointment and drive back home, leaving my plans of track fun behind me. I got my car back to the dealer and they're currently replacing the MC. I'll let you know later whether this will solve the problem or not. I'm not particularly optimistic, though, because the dealer gave me a brand new (1,300 mi) loaner Cayenne to use while they fix my car and, guess what, the Cayenne's brake pedal sinks exactly like my car's! I did a search on web forums and found other people who noticed the same thing, including in brand new cars still sitting at the dealer's parking lot (check http://forums.rennlist.com/rennforums/997-...th-brakes.html).

I think a sinking brake pedal is tricky to notice because the pedal feels firm at first, and under normal driving the car brakes just fine. You'll only notice a problem if you deliberately keep pressing the pedal after you come to a stop, which I only did after I first flushed the system and was testing for potential problems. I think this problem may go unnoticed for months if you're not paying special attention to your brakes.

Do you test your brakes regularly for a sinking pedal? Is this a cronic problem with some of the newer models, or just "normal"? If "normal", how low can you (or the brake pedal...) go???

Have never experienced on my C4S or any other car for that matter. It is not normal and needs to be sorted out before you take the car back to the track.

[carvalag]

Thanks. Yes, the dealer replaced the master cylinder and the pedal feels great now. I did notice that in cars with power brake assistance (like my X5, for instance) the pedal will sink a bit when the assistance kicks in, if you keep it pressed hard enough for a few seconds. It doesn't nearly go the floor as mine was doing, though.