Intermittent Braking Fault

[amp33385]

I have a Cayman S which basically has almost zero braking maybe one time in 20. On the other occasions it brakes ok.
When it doesn't work properly the pedal stays firm rather than going to the floor but just doesn't slow the car down properly
The front discs & pads were approaching the end of their life but there was no odd braking noises / other signs of a fundamental problem
I asked the garage to check it out & change the discs & pads. Their assessment is that there is no obvious fault anywhere in the braking system, they can't replicate the fault but having changed the discs & pads say the brakes are miles better
Has anyone had a similar intermittent problem or have any ideas what the problem might be - I am surprised that just changing discs & pads has solved this

[Pope]

That's some serious lurking there old bean......................



Possible servo problem? how old is the car and if you brake all the vacuum out of the system (engine off) does it restore quickly once restarted? Does the pedal always return quickly? (ie: follow your foot back up instantly)

[graemel]

good lurking amp. Are you sure that it's not the anti lock brake system cutting in. How hard are you braking when this happens ?.

[davek_964]

I had a similar problem many years ago on my 964 - although it was more repeatable, and would happen every time I braked hard. I would get initial bite, but then the pedal went hard and the car shot forward. It took quite a while for the cause to be found, and it turned out to be an accelerometer sticking because it had got clogged up with iron filings.

I'm sure the Cayman S has a quite different system to a 21 year old 964, but I suspect you may have a similar kind of problem - that something electronic is confusing the car. If by any chance the Cayman does use accelerometers as part of it's braking system, it would be worth a check.

[amp33385]

The car is just over 4 years old. It definitely isn't ABS / hard breaking - a couple of the times were around town & not very hard breaking.
It is still at the garage - I can't pick it up for a couple of days so can't test how the pedal behaves etc but don't really know what else to get them to do
The fact that it is so intermittent seems the most odd but I don't know enough to say what that isolates it to

[Henry-F]

Pope said:

Possible servo problem? how old is the car and if you brake all the vacuum out of the system (engine off) does it restore quickly once restarted? Does the pedal always return quickly? (ie: follow your foot back up instantly)

Yep, first thing I thought when I read it was the brake servo.

Henry

[cd1957]

Hi have you checked around the battery for water,it should not get past the servo connection tubes,but there is always a first time,as the early 996 used to fill servo with water,modified pipes now available.Does the car feel as if the brakes are releasing just as you are about to come to a stop?,had this before,one of the ABS sensor looms was faulty.

Chris

[Tinners1983]

Sorry to drag this up, but did you get this sorted? I now have the same problem on my 2006 987 CS. Just replaced the vacuum pump which has improved braking all round, but still get this low speed issue. The pedal doesn't go hard, it goes to the stop and the car comes to a very gradual stop

[Pope]

I seem to remember an inertia type valve near the front tub that failed a few times - but may have been 9x6 rather than 9x7; generally reducing brake pressure when it went bad. Check in the brake circuit for an in-line valve - or on PET??