Just today the brake peddle lost pressure on my 1990 Volvo 760 Turbo Wagon. The peddle doesn't quickly go right to the floor but feels squishy and slowly goes down. There is a loss of pressure. There is a kind of hissing noise as you push on the brake peddle. Breaks still work somewhat but not great. There is no visible brake fluid under the car or under the hood, The reservoir is full. Thank you for any help

 

Hissing noise is the power brake booster, check under the hood for vacuum line leak. Have somebody step on the brake while you listen for the leak. The pedal to the floor could be the master cylinder, leaking pressure internally. Not expensive or hard to fix either one.