* Internal Leakage: The most likely culprit is a failure of the internal seals or pistons within the master cylinder. This allows brake fluid to leak internally, bypassing the mechanism that applies pressure to the brake lines. The "thushing" noise might be the sound of fluid leaking or parts moving abnormally due to the internal damage. With no pressure building up, you'll have no brakes.
* Low Brake Fluid: While a low brake fluid level *could* lead to no brakes, the "thushing" noise points to an internal problem *causing* the low fluid. It's highly unlikely the fluid simply leaked externally without some internal damage manifesting as the noise.
* Seized Piston: Less likely, but possible, a piston within the master cylinder could be seized. This would prevent proper movement and pressure buildup, leading to no braking. The "thushing" might be the piston struggling to move.
* Air in the System (Less Likely): While air in the brake lines *can* reduce braking effectiveness, a complete lack of brakes and a "thushing" noise strongly imply a more significant internal master cylinder problem.
What you absolutely MUST do:
* Do NOT attempt to drive the car. Driving without brakes is incredibly dangerous.
* Have the vehicle towed to a qualified mechanic. This is not a DIY repair; improper handling of brake systems can be extremely hazardous. The master cylinder needs to be inspected and replaced.
The master cylinder is a critical safety component. Ignoring this issue is extremely dangerous and could result in a serious accident. Get it fixed immediately.
