Audi Repair: Audi brakes, power brakes, audi models

Question
the brake light on my 1990 audi quattro comes on every now and again and the brakes feel like there is no power brakes (very hard).  i checked the fluid and it is full.  i saw a resevoiur that said hydraulic fluid.  does it need that as well as brake fluid?

Answer
No, the audi system uses Pentosin, which is special fluid, rather expensive but cannot be mixed with any other fluid. Check since some audi models do use regular hydraulic fluid.   The brakes do use normal brake fluid.  Normally when you see this problem, the Nitrogen Bomb has lost its charge and needs to be replaced.  This nitrogen provides some braking assistance when the power assist pump is switched off, so if you notice hard pedal, the system probably needs to be checked out.  Let me know what you find,  Jan