986 Forum - The Community for Porsche Boxster & Cayman Owners - View Single Post - Brake pedal stops normally then slowly fades to floor. Master cylinder? Booster?

Rotmilky · 06-26-2017, 07:35 AM

I took my '01 S to an autocross this weekend. It was close to 100, so hot, but not outrageously so. When leaving the autocross, I stopped at a red light. I noted the braking power was pretty normal. But as I sat at the light, the pedal very slowly lowered to the floor. Something like 6 seconds to go from stopping to lowering to the floor. If I released the brake, it would once again stop in the normal position and then slowly lower (as long as I maintained steady pressure on the pedal).

Fluid was replaced with Bosch fluid a month or two ago and bled. I'm pretty sure those symptoms aren't brake fluid boiling symptoms. I get normal brake feel and travel initially.

So, I'm guessing either master cylinder, bad brake booster or vacuum leak. The engine seems to run normally. No idle issues, etc. Pedal stiffness is normal. So I'm ruling out booster and vacuum leak. However, I have read some threads out there on brake boosters having some water in them. Those symptoms are a little like mine, but not identical. If it's not that, then the only thing left is the master cylinder as my remaining suspect.

That said, it's possible I haven't considered something. Anyone else out there have this problem?

06-26-2017, 07:35 AM	#1
Rotmilky Registered User Join Date: Feb 2017 Location: New Mexico Posts: 42	Brake pedal stops normally then slowly fades to floor. Master cylinder? Booster? I took my '01 S to an autocross this weekend. It was close to 100, so hot, but not outrageously so. When leaving the autocross, I stopped at a red light. I noted the braking power was pretty normal. But as I sat at the light, the pedal very slowly lowered to the floor. Something like 6 seconds to go from stopping to lowering to the floor. If I released the brake, it would once again stop in the normal position and then slowly lower (as long as I maintained steady pressure on the pedal). Fluid was replaced with Bosch fluid a month or two ago and bled. I'm pretty sure those symptoms aren't brake fluid boiling symptoms. I get normal brake feel and travel initially. So, I'm guessing either master cylinder, bad brake booster or vacuum leak. The engine seems to run normally. No idle issues, etc. Pedal stiffness is normal. So I'm ruling out booster and vacuum leak. However, I have read some threads out there on brake boosters having some water in them. Those symptoms are a little like mine, but not identical. If it's not that, then the only thing left is the master cylinder as my remaining suspect. That said, it's possible I haven't considered something. Anyone else out there have this problem? __________________ V.H. Whitley Owner of Waaay too many vehicles Non Porsche :1959 International B120, 1960 International B120, 2015 BMW M3 Porsche: 1997 986, 2001 986S, 1968 911L, 1968 911S, 2005 911, 1984 928, 2008 Cayenne S.