Two problems related to brake foundation components have been reported for the 1999 Audi A4. The most recently reported issues are listed below.
Wet braking performance is miserable! and dangerous- many second delays.
After traveling for several minutes on freeways in rain storms the first application of the brakes does not slow the car. There is a 1-2 second delay before there is any barking force regardless of pedal pressure. This isn't merely the typical lack of initial bite on wet brakes as with wet brakes the brake force will increase with increased pedal pressure. When this happens, instincts are to press the brake harder and when the water is finally shed the car will pull sharply in reaction to which ever of the brakes 'dries' first. Audi has designed and sells a plastic wing that fits around the inside of the wheel well at the underbody/wheel well interface to combat this but it only makes a marginal improvement. In addition, the 2002 Audi A4 comes equiped with this same shielding in an apparent awknowledgement of the issue.