I have a Volvo V70 R 1998. During braking when descending down certain hill roads, not all by any means wet or dry, the brakes sometimes vibrate and loose efficiency. Hard braking on the level or uphill no problem? Any advice greatly appreciated.

 

Well, dissipating brake heat has been a major issue for all cars ever made, always. That is the biggest reason cars use disc brakes today. However, even with discs, they will still get hot enough to glow, and it really doesn't take all that much. Your description sounds like it's true of every car ever built, but obviously "certain hill roads" might have to be interpreted to be pretty impressive.

 

Brake rotors are warped; replace them. Most likely the fronts, but maybe rears as well.