hi guys i own an Audi A4 B5 1.9 tdi with 115 bhp 2000 reg. i am having terrible trouble with the brake system. i suspect it is vacuum pump related. when the car is trying to stop there's like there is no there at all, the brake effort does not match the brake force. The lower the rpm the worse the brakes get. the brakes are not as bad when the revs are high but are still pretty bad. in my opinion this car is not safe to drive on any public road as the brakes are dodgy. I checked the vacuum lines and i cant not find any cracks or erosion in the lines. is this a known problem or has anyone had this problem before? any information would be very helpful and much appreciated.

p/s this car has been to a mechanic and he could not find anything.