Q: When I apply the brakes in the car they hiss. It sounds like a constant flow of air escaping. The brakes are also hard to push. What could be the problem?
A: The brake vacuum booster may be defective. The brake booster works off engine vacuum to give your car power brakes. The hissing sound indicates a possible leak. Without enough vacuum, the power brakes are no longer working as designed. Since driving without power brakes could be hazardous, have the vehicle towed to a qualified service center.