Two problems related to brake disc pads have been reported for the 1999 Audi A4. The most recently reported issues are listed below.
This car seems to have a serious problem during wet braking. After numerous occurrences, I was forced to spend $400 to replace the stock pads that may cause this problem. With the new brake pads, no re-occurrence yet. Manufacturer seems inattentive to this. Perhaps NHTSA can contact manufacturer regarding this issue as I'm not the only owner to experience this.
There has always been a problem with the braking performance of this vehicle during wet conditions. This is only during highway or country driving where the brakes are not frequently applied. When brake pedal pressure is applied during these conditions, there is approximately a 1 to 2 second delay before the brakes start to retard speed. It feels or seems like there is a film of water between the discs and pads and this hesitation is occurring while squeezing or drying out this film of water.