New Yorker V6-3.5L VIN F (1994)
A residual pressure check valve is usually included immediately under the brake line connection on hydraulic assist power brakes. This valve maintains a
slight hydraulic pressure within the brake lines and wheel cylinders or caliper to give better pedal response. If it is sticking, the brakes may not release.
Power brakes that have a hard pedal are usually suffering from a milder form of the same ills that cause complete power unit failure. Collapsed or leaking
vacuum lines or insufficient manifold vacuum, as well as punctured diaphragms or bellows and leaky piston seals, all lead to weak power unit operation.
A steady hiss when the brake is held down means a vacuum leak that will cause poor power unit operation.
Do not immediately condemn the power unit if the brakes grab. First look for all the usual causes, such as greasy linings, scored rotors or drums. Then
investigate the power unit. When the trouble has been traced to the power unit, check for a damaged reaction control. The reaction control is usually
made up of a diaphragm, spring and valves that tends to resist pedal action. It is put in the system to give the pedal "feel."
