Vincy

Gentleman, I really need your help with this. The dealer cannot fix the sinking brake peddle. They put in a new master cylinder, no improvement. Then they did a special bleeding procedure, again no effect. Now they are waiting on rear brake pads. I don't see how this can help since the ones on there are like new.

Does anyone have any suggestions? Thanks.

https://rennlist.com/forums/997-turbo-forum/363089-sinking-brake-peddle-even-with-a-new-master-cylinder.html

B-Line

I'm at a loss. But I am certainly no wrench..

If I were you, I would start spending a great deal of energy documenting the problem/history.
What day you dropped off the car for service.
How many days it has been in for service.
What were the results of each service visit.

I would start making written requests to the dealership. I want the brake calipers, pads, lines, etc. changed and replaced. I would send stuff, in the mail, registered, receipt return etc..

Not only is there potential liability if something should happen to your car, (especially a brake failure..) You will also need documents, should you decide to pursue a lemon law action.

I would also have a third party mechanic, drive the car, test the brakes, and sign a written affidavit (notarized) that the brake pedal is not working properly.

B

Dan993

Pads would have no impact on sinking pedal. This would likely be caused by:
1. Air in the lines
2. System bypassing. Master cylinder, ABS valve, etc.
3. Fluid leak
4. Issue with Power Brake Booster

This system is not new technology and should not be difficult to diagnose/repair. You should also push for the regional or national technical rep to get involved.

TT Gasman

That's unacceptable, there are only a few things that can cause something like that, worst case they can replace the whole brake system. Def get the regional guys involved

whyb2nd

Hydraulic issues no doubt, but that's bull sh*t with a 130K dollar new car. Good luck and stick it to them.

Vincy

The car is still in the shop. They told me I abused the brakes and the pads were crumbled, this is nonsense, the car has only been on a couple back roads and never on the track. They replaced the ABS module with no effect. Now they say they are rebuilding the calipers. The dealer says they have to do what Porsche tells them to do. This is my first Porsche and I'm discouraged, thinking I should have gotten something else. I think the dealer is doing what they can do and I'm trying not to stress out, but its over 3 weeks now in the shop.

Vincy

Who are the regional guys?

Edgy01

PCNA maintains guys at regional levels as a go-between for them so they in Atlanta don't have to tackle all the issues from the dealers. Those guys are empowered to resolve this sort of stuff.

insite

when you first press the pedal, does it feel firm and then start to sink if you keep pressure on it? if so, you have a fluid leak. this can really be from anywhere, but most likely it's a caliper piston. pressing the pedal and holding it until it hits the floor about five or six times should expel enough fluid to leak from the outer caliper seals (fluid can leak past the inner seals and never hit the pavement; you have to press the fluid past the outer seal as well). it should be obvious where the fluid is coming from. the brakes on these cars are generally first class; don't be discouraged. they will fix it.

Vincy

insite, thanks. Yes there is an initial firm feeling then sinking. You can pump it up but then it sinks again. But there is no leaking fluid anywhere and the master cylinder is full. Its still at the dealers and they said something about "regional guys". I'm discouraged and asked Porache to do a buyback of the car. I don't know what will happen about my request. I predict they think its fixed and return it to me and it happens again. I say this because the dealer said it didn't happen and then did happen. They said they may rebuild the calipers, and I'm concerned this will cause only more problems down the road. Thanks for your suggestions.

eclou

Vincy,

I would recommend getting an attorney to draft a letter to the GM of your dealership and PCNA regarding the liability of returning a car to you with defective brakes. I think that will light a major fire. You might seek the advice of someone here who might do it as a favor. I know "Frayed" on the Gt3 section is knowledgeable about product safety issues.

Vincy

Now the dealer has me totally confused. They say the brakes are fixed but the pedal still sinks, they say it sinks less than before and now the sinking is at a normal level.

If you are stopped and press hard on the pedal, about like a moderately hard stop, and keep the pressure on the pedal sinks in about 4 seconds till about 2 inches off the floor. I told them this was wrong. So they let me start a new TT and hold the pedal, and it did the same thing, sinks in a couple seconds.

I thought I remembered the pedal being hard, but I couldn't argue when the new TT pedal was the same, soft and sinking.

Can you guys try this? Start the car, keep it in park, and apply the brake. Does your pedal sink? My car is a tip. My imagianation usually doesn't play tricks with me when I'm sober, which I am. Thanks for your help.

AAHTT

I checked mine for you and my brake pedal has a motion range of about 2 inches and it stays put no matter how hard you push or you wait. it stays about 3 inches above the floor all the time.
my car is manual.

jrok

I had a similar problem on my previous 911. I would come to a stop at a stoplight and everything seemed normal. Almost immediately after coming to a stop the pedal would begin sinking to the floor just as you described. My problem was diagnosed as a faulty ABS pump/valves/solenoid - the mechanical part, not the control unit. Somehow, the pressure was bleeding through the valves in the ABS unit or something like that. The unit was replaced and the problem went away. Don't know if this is your problem but I didn't see it listed in your responses.

cviles

I've just gone around an around with this same problem on my 987S. First thing done was to replace the master cylinder and things were fine until I tried to prep my car for my next track event -- the same sinking pedal came back. If the car was let to sit for a few days (or even just trailored to the dealership) the problem went away, so nothing was done about it. A month went by, and my next track day came around. After bleeding the brakes the sinking pedal came back again, that was two weekends down the tubes over this issue.

In that time, I did the same thing you did -- sat in other cars and compared the brake feel. One of the new! Boxsters had a worse pedal feel than mine. A loaner Cayman was fine; my 997S is fine. I think a certain number of cars just have bad/marginal parts from the factory and most drivers just accept it.

Eventually, the hydraulic pump and master cylinder (again!) were replaced. Now the pedal is firm like when the car was new. The current theory is that a seal in my first bad master cylinder disintegrated and debris damaged the valves in the hydraulic pump, so these two items should have been replaced the first time around.

At one time I thought I was the only person with this problem, but the dealership confirms that other cars have had this identical problem. The only correlation seems to be that we drive the car hard, but the dealer has tried to correlate using Super Blue brake fluid as the cause. I don't use Super Blue; it was only in the car once when I ran out of fluid at the track trying to (non-existent) bleed air from a system with a bad master cylinder. Even still it's a DOT4 fluid and supposed to be compatible with other DOT 4 fluids, so I don't think that's the issue.

Both times, the parts and labor were covered under warranty even though I track the car. I doubt they'd cover it again though, but now the brakes are fine.

Long story short, have both the master cylinder and the hydraulic pump checked out. The pedal should not sink, but should be firm after a short travel distance. More pressure should compress the pedal further but it shouldn't continue to slide.