My A4 tdi 130 sport, has twice had the issue of the brake pedal going hard, as if the servo has failed. If it's left for 10 mins the pedal works as it should (I have had the servo replaced a number of years ago when it failed completely, that time the lack of vacuum effected the performance of the car as well).Obviously I want to sort this out soon, as I don't want the pedal to go hard when I need it, but don't want to buy a new servo if it's something else. Also I was told that vw passats of similar age had a recall on the brake servo but the A4 didn't. I have checked for any lose pipe work etc but all seems ok, the only thing I could find is that the scuttle around the servo was half full of water - thanks to a blocked drain hole, could the water have entered the servo at all? Any ideas work be gratefully received.
thanks in advance.