Prodrive

Hi all, i have a cayenne 3.0tdi 2012 EU version with a problem in the brake pedal, when I start it in the morning the brake pedal works correctly, when the engine temperature reaches 90 ° the brake pedal is sunk about 3cm, I have to put my foot under it and lift it, I have changed the brake master cylinder and brake booster, nothing has changed, someone had a similar problem?

Thanks in advance.

garrett376

More history would be helpful: Why did you change the master cylinder and brake booster in the first place?

KBell

Never heard of this.
Interested.

Prodrive

In the first place, I changed the brake fluid because the owner of the car told me that he tried to change it at home, I did a purge with the machine without any result, then I changed the pump and then the brake booster. I have noticed that with the new booster it takes a long time for the pedal to sink, I have to circulate about 1 hour, with the old booster just after reaching 90 degrees the pedal stopped working.

Neither do I, nor do my mechanic friends, I've never seen anything like it.

garrett376

If I understand correctly, this was never present until the first guy bled the brakes?

If so, your description doesn't mention it, but did you do the proper bleeding of the PSM/ABS module?

If you are not losing fluid, then the master cylinder is bad, or you just need to do a proper bleed. What "machine" are you using to bleed?

Prodrive

I don't know the story, the owner doesn't seem to want to tell me the truth... you mean 2 master cylinders are damaged?

I have also purged the abs module electronically.

With the engine cold, the brake pedal works perfectly, I don't think it's a bleeding problem.

figure1a

With all this DIY work being done to the car without anyone really knowing what they are doing, I would not drive this car. You are potentially looking at a catastrophic brake failure.

garrett376

How did you do the brake bleeding procedure, and the PSM/ABS module bleeding? Knowing your exact steps would be helpful.

And confirm: no loss of fluid level, correct?

Prodrive

I followed the steps indicated by the diagnosis, the problem is not a soft pedal, the pedal is hard, it just doesn't come back when you step on and release your foot, that's why I don't think it's a bleeding problem.

garrett376

Did you fully pump the pedal during the bleeding process?

Prodrive

If my memory doesn't fail me, yes.
I will try again tomorrow

garrett376

What you are describing sounds very familiar where the system is bled, but the master cylinder is not completely. This occurs with clutches and brakes where the master cylinder runs dry or is replaced; pumping the pedal for its full travel when bleeding at each corner is essential if you've changed out the master cylinder - lots of reps done slowly to get any air out is important. My bet is you have a bubble in the master cylinder part of the circuit (barring any other issues like leaks from the system).

CAVU

Since we do not know the year of your Cayenne or your location, if you are driving a US version, you may want to check this recall before doing much more. https://static.nhtsa.gov/odi/rcl/201...6V169-7650.PDF

You can go to the NHTSA site and load your VIN for a definitive answer.

Prodrive

2012 EU version

CAVU

might be worth a check through your EU site or just give your local Porsche dealer a call.