2019 Cayenne S ceramic brakes not working when wet

[lynnhughes67@hotmail.com]

I bought a 2019 Cayenne S with Ceramic brakes from a Porsche dealer during July 2022. I noticed that when the brakes were wet after a car wash there was a second or two where it felt like the brakes had completely failed. However when they do grab then everything was fine after a few applications Of the brakes. Didn't encounter this problem in normal rain however felt it again briefly in December in heavy rain on the M4 when I need to drop a few mph. In January, again in heavy rain, needed to brake relatively hard on the M27 and it took a full second before the brakes grabbed. Terrifying. Car back with Porsche For 3 weeks now …. Doesn’t feel like there is much progress with the diagnosis. Any ideas or similar experiences ?

 

[Scrounger]

Yep. Similar experience on my 718 GTS this morning. I put it down to the discs having surface water on them. a couple of good pushes and it was fine. Agreed, not good if driving in heavy rain.

Dan

 

[Motorhead]

Chaps, I may be wrong on this but I thought that the braking system pre-arms the brakes to bring them into light contact with the discs and skimming the surface? However, it may just be that this happens only if you were to do an emergency stop and the ABS system senses this (the time from accelerator release to brake application maybe?) to reduce the brake application time.

Jeff

 

[AndrewCS]

I thought that the braking system pre-arms the brakes to bring them into light contact with the discs and skimming the surface ?

Some cars do, not sure which though ... I always assumed that my 981 Cayman S did given it`s excellent braking performance in the wet - when the brakes were unused for a while

The GT4 is totally the opposite - I am sure that it does not `automatically skim` the discs hence I occasionally and lightly `left foot brake` during prolonged inactive brake periods

EDIT ... comments here are relative to iron - steel brakes only

 

[lynnhughes67@hotmail.com]

Many thanks for the replies above. I am obviously concerned as a 1 second delay in the brakes grabbing equates to a travelled distance of 88ft at 60mph. While Porsche have had the car 3 weeks and confirmed they experienced the problem having hosed the wheels down they are yet to provide a coherent view of the problem. Not sure how long is reasonable for them to diagnose

While I suspect the advice about occasional application of the brakes to keep them skimmed /dry is very helpful I would not expect to need to do this in what is in essence a premium large family car. I would expect the brakes to work at all times at a level of performance that is comparable or better than all other cars I have owned.

This delay in the braking Is unlike anything I have ever felt before. It is almost as if the car continues to drive and fight the brake. on the motorsay it is almost as if cruise control has not disengaged and is attempting to maintain speed.

While I would naturally assume a physical problem when dealing with brakes I start to think about software.

keen to hear from anyone with similar experiences or get advice.

thanks

 

[johntamarhudson]

Historically, the way that ceramic discs work with the brake pads is that when you apply the brakes, the brake friction from the pad fills the minute pores in the surface of the disc. It is the friction in these pores that work with the brake pad to provide friction to stop the vehicle. When you go through a ford or apply strong water pressure onto the discs when cleaning the car (with a pressure jet) some of the friction material is washed out of the pores. When you apply the brakes after this, it takes a few milliseconds for the pores to fill with friction material again and you have normal braking service. But it is milliseconds not seconds, but still noticeable.
Ask Porsche if this is still the case.

 

[lynnhughes67@hotmail.com]

Thank you for the message about. It is hard to judge the exact delay in braking however I am confident it is not millisecond - the engineer that road tested the car, like me, had never experienced this kind of problem.


This evening‘s update for Porsche is that the problem is due to some kind of contamination however they are not specific and are suggesting the only resolution is to replace the discs and pads !

Would be interested in hearing of any experiences of ‘contamination’

 

[Stannards]

Hi I’ve got a 2019 Cayenne turbo,s hybrid with ceramic brakes. I’ve had so many instances where the brakes appear not to work when cold or wet. Several times on motorways after driving with cruise-control on for several miles in wet or cold weather. When you need to brake there is no response when you first push the pedal It almost feels like you haven’t got any brakes until they dry/warm up. Which is fine at slow speeds but at motorway speed 70/80 mph it’s quite alarming. Especially as the car weighs nearly two and a half tonnes. And being a hybrid you don’t get any engine braking unless your driving in sport or sport plus . I’ve mentioned it to my local Porsche dealers service centre who told me it’s my responsibility to keep dabbing/lightly applying the brakes in cold/wet weather to keep them dry and maintain some heat which is ridiculous as every time you touched the brakes it would disengage the cruise control . I pointed out that my other car with ceramic brakes have a braking system that keeps the pads/disks pre-armed and ready. I’m slightly relieved to see it’s not just me as the dealer insinuated. I previously had a Cayenne turbo with steel brakes which were so much better than the brakes on this car so I’m thinking of changing back.
Thanks

 

[lynnhughes67@hotmail.com]

That is really interesting. a copy of the notes between the dealer and the Porsche technical department was shared with me. Within these notes there is a reference to a brake wipe function which has been switched off. This function would gently apply the brakes if the windscreen wipers are switched on and the brakes hadn’t been used for 5 minutes. No explanation of why it is now switched off. I have replaced the pads on the front now and the brakes are back to what I consider normal. The Porsche dealer wanted to replace the pads and discs on all wheels at a price of £17k despite not giving me a diagnosis I was satisfied with.

 

[Stannards]

After reading your comments I’m going to go to the dealership tomorrow and try and sort it out. It seems to me that’s the sort of thing that could happen. But why a function like that would be able to be switched on/off when surely it’ a safety feature doesn’t seem right.