I am looking a 1996 volvo 960 to buy when you step on the brake pedal it is very hard and makes a hissing sound almost like a vacuum line off or lose inside the car not under the hoos and the motor shutters at the same time when you are stepping on the brake pedal can anyone give me an idea what this could be i thinking brake booster but i thought the pedal would be spongy ?

 

most likely a leak on the brake booster. spongy is when u have a leak on hydraulic system