Brake pedal pulse in the wet

[GreggT]

Anyone heard of this?

Wife's C4S with under 10K and a baby'd car........on a drive trip to VA, in the rain at interstate speed, I feel an anoying pulse in the pedal with brake application. Much slower pulse than ABS and if I had to liken ot to anything it would be the way a warped rotor feels. A couple days later, the sun is out.....it occurs to me that the brakes no longer have that feel. They are fine.

I asked for an opin at the dealership and they gave me an explanation I had never heard before.

Rain sensor tells brakes that it's raining. Brakes then (automatically) engage in light periodic action to keep them warm and dry.

When I do apply brakes for real there may exist some glazing on the rotor or pad that causes what I feel...........also that my lower offset Techart wheels may be contributing to or agrivating the problem.

OK so it all sounded like a fairy tale to me, but I just listened.

Does the rain sensor on a 997.2 really provide info to the braking system?.......is lower wheel offset really the cause of all evils known to man?......and what is the real solution to world hunger?

TIA

[wwest]

Anyone heard of this?

Wife's C4S with under 10K and a baby'd car........on a drive trip to VA, in the rain at interstate speed, I feel an anoying pulse in the pedal with brake application. Much slower pulse than ABS and if I had to liken ot to anything it would be the way a warped rotor feels. A couple days later, the sun is out.....it occurs to me that the brakes no longer have that feel. They are fine.

I asked for an opin at the dealership and they gave me an explanation I had never heard before.

Rain sensor tells brakes that it's raining. Brakes then (automatically) engage in light periodic action to keep them warm and dry.

When I do apply brakes for real there may exist some glazing on the rotor or pad that causes what I feel...........also that my lower offset Techart wheels may be contributing to or agrivating the problem.

OK so it all sounded like a fairy tale to me, but I just listened.

Does the rain sensor on a 997.2 really provide info to the braking system?.......is lower wheel offset really the cause of all evils known to man?......and what is the real solution to world hunger?

TIA

First, the rain sensor results in the calipers getting a light, constant, precharge, so that shouldn't be the source of the pulsing.

The "pulsing" you describe is the same feeling I get in our '01 F/awd RX300 when applying the brakes lightly in the wet and on a slight downhill incline. The dealer ascribed it to the EBD, Electronic Brakeforce Distribution, the automatic, dynamic, shifting of braking forces front vs rear to take optimal advantage of braking at both ends.

[GreggT]

Anyone heard of this?

Wife's C4S with under 10K and a baby'd car........on a drive trip to VA, in the rain at interstate speed, I feel an anoying pulse in the pedal with brake application. Much slower pulse than ABS and if I had to liken ot to anything it would be the way a warped rotor feels. A couple days later, the sun is out.....it occurs to me that the brakes no longer have that feel. They are fine.

I asked for an opin at the dealership and they gave me an explanation I had never heard before.

Rain sensor tells brakes that it's raining. Brakes then (automatically) engage in light periodic action to keep them warm and dry.

When I do apply brakes for real there may exist some glazing on the rotor or pad that causes what I feel...........also that my lower offset Techart wheels may be contributing to or agrivating the problem.

OK so it all sounded like a fairy tale to me, but I just listened.

Does the rain sensor on a 997.2 really provide info to the braking system?.......is lower wheel offset really the cause of all evils known to man?......and what is the real solution to world hunger?

TIA

First, the rain sensor results in the calipers getting a light, constant, precharge, so that shouldn't be the source of the pulsing.

The "pulsing" you describe is the same feeling I get in our '01 F/awd RX300 when applying the brakes lightly in the wet and on a slight downhill incline. The dealer ascribed it to the EBD, Electronic Brakeforce Distribution, the automatic, dynamic, shifting of braking forces front vs rear to take optimal advantage of braking at both ends.

Thanks.....I may have missunderstood the explanation that had been giving me but.....don't think they meant there was a direct cause-effect of the 'pre-charge' to the pulsing I feel.....but rather over time and with rain, somehow a glaze or thin transfer takes place.....then when I apply brakes the result of that is felt......I don't know.

As for the "auomatic,dynamic, shifting, of breaking forces......" well if that's it, then it's unacceptable. Porsches have better than average brakes. I did not have this on 993 nor 996 and presently not on Turbo. I can't believe they've built this odd feel into a 997.2

Appreciate the observation but think I will continue to persue another explanation.......and solution.

As I said....car is wife's and baby'd.....pads & rotors have had a very easy life so far. I may try to run them through a normal bed in myself a weekend soon......then wait for some rain.