Asking for opinions

[Tony Lum]

Guys,

I thought I'd put this out and see what others think.  The subject is my 1980 Audi 5000S (type 43).  Its always had this little quirk where braking power seems inverse to applied force.  If you stomp on the brakes, you get very little assist.  However, if you step on the brake pedal and apply increasing force, you get all the braking you desire.  

When I first got this car (1986, my first Audi years ago!) it had this symptom.  It had the Teves calipers on it, so I upgraded to the Girling G54 calipers and 280MM rotor from the T5000 turbos of that era.  I also have the rear disc brakes from the same.  Made no difference in the brake function.

My thought is that its something to do with the vacuum booster.  The standard test is to depress the pedal slightly and start the engine and the pedal will pull in as vacuum builds and it does that.  But I never been completely happy with this syndrome and was wondering if its worth it to replace the vacuum booster.

TIA,

Tony

'80 5000S 
'83 ur-quattro
'87.5 coupe GT Special Build
'01 A4 Avant quattro 2.8