How to troubleshoot a malfunctioning brake system in an Audi 80?

I recently noticed that my Audi 80's brake system is not functioning properly. Sometimes it takes longer for the car to come to a complete stop and I can feel the brakes vibrating. What could be causing this issue and what steps should I take to fix it?

It's possible that there may be air in your brake lines. Bleeding the brakes and removing any trapped air can greatly improve brake performance. Make sure to use a vacuum pump for the best results.