996 funny brake noise

johnoscar · 25 Apr 2013

Hi there, any ideas would be welcome.....
When I brake softly at low speed, below 20mph I get a strange pulsing through the brake accompanied by an intermittent almost buzzing sound with the pulse. The only way I could describe it would be to say it feels a little like a warped disc although all discs are brand new with pads????? As I say no problem under harder braking or about 25mph no loss of performance all feels well above low speed. Thanks

wells · 25 Apr 2013

Sounds like your ABS is cutting in to me? :?:

Red993C4 · 25 Apr 2013

wells said:
Sounds like your ABS is cutting in to me? :?:

Which you wouldn't normally expect below 25 mph unless the car is on a low-friction surface. :dont know:

Is the car on non-standard tyre sizes or are tyre pressures too low? :?:

johnoscar · 25 Apr 2013

Good call, thinking about it sounds like abs kicking in, I will try turning the traction control button off (pds) or whatever its called. Had it on ramps today at a garage new discs and pads all round and still doing it. Everthing looked fine apart from CV boot split and grease around brake and hub?????Could that cause the ABS to kick in?

johnoscar · 25 Apr 2013

Sorry should say new to Porsche as in 5 days, no idea what tyre pressure should be or tyre size and make. I believe they are set to 32psi.

Red993C4 · 25 Apr 2013

johnoscar said:
Sorry should say new to Porsche as in 5 days, no idea what tyre pressure should be or tyre size and make. I believe they are set to 32psi.

Which tyre sizes are fitted to your car? Recommended pressures frequently differ, depending on tyres fitted.

johnoscar · 25 Apr 2013

Continental front 205/50 zr17 rear 255/40 zr17

Red993C4 · 25 Apr 2013

I don't have your model's tyre pressures readily to hand but I'm sure someone will be along shortly with the information.
If it hasn't been removed at some stage you should also have a sticker showing the correct pressures somewhere on the car. On your car it was probably on the underside of the boot lid or on the inside of the petrol tank flap. On later cars it's inside the door jamb of the left-hand door.

wells · 25 Apr 2013

Pulsing and buzzing has to be ABS activation. I'm not sure way, but I think you need someone to check it out.

johnoscar · 26 Apr 2013

Thanks, now in the cold light of day I think it must be ABS activation

Red993C4 · 26 Apr 2013

johnoscar said:
Thanks, now in the cold light of day I think it must be ABS activation

Have you been able to confirm yet that tyre pressures are correct?

johnoscar · 10 May 2013

ABS ring

Turns out that there is a crack in the ABS ring with a small chunk missing from the ring so at slow speed the car thinks the wheel is locking up and ABS kicks in.