Q: 2006 Audi brake pedal hard replaced booster with no results

To begin with the booster needs a vacuum source. You said you replaced the line, but there is a check valve in the line, it is probably installed at the booster end of the line. It looks like just an elbow fitting, but it’s in fact a check valve that allows the vacuum to build up in the booster. Also be sure the fitting where the line is connected to the engine is pulling a strong vacuum. It should be strong enough that it tries to suck you finger into the engine. After you’ve verified that those things are OK, check to see that there is free travel on the pushrod when the brake pedal is returned. There should be about a quarter inch of free travel at the brake pedal before the rod begins to actuate the booster. Another thing that is harder to check is the free travel between the booster and the master cylinder. This job requires some special measuring instruments and the separation of the booster from the master cylinder. But if there is no free play between the booster and the master cylinder, the brake pressure will build up, locking the brakes and making the pedal hard. If you contact Your Mechanic, they can send a technician to your home or office to check out your brake system and advise you about the next steps you need to take.