Power Booster Hydro Booster

Answer to “All the following can cause a hard brake pedal except:”

Low engine vacuum: If there’s low engine vacuum, the vacuum booster won’t receive enough vacuum to assist the brake pedal, resulting in a hard pedal.
Ruptured brake booster diaphragm: A ruptured diaphragm prevents the pressure differential needed for the booster to work, leading to a hard pedal. It can also cause a vacuum leak and engine stumble.
Slipping power steering belt: The power steering belt drives the hydro boost unit. If it’s slipping, the hydro boost unit won’t generate enough pressure to assist the brakes, causing a hard pedal.
Air in the hydraulic system: Air in the hydraulic system causes a spongy brake pedal, not a hard one. This is because air is compressible, leading to a feeling of softness and lack of firm pedal resistance.