There are two purposes for the Honda brake master cylinder on your vehicle. It is the device that compresses the hydraulic brake fluid so force can be applied to stop the vehicle. It is also the place where reserve fluid is stored for use in the future. The location on your Honda of the brake master cylinder is on the driver's side of the engine compartment on the upper section of the firewall. It is directly mounted to the brake vacuum booster. There is a mechanical lever from the brake pedal that depresses the piston in the brake master cylinder that creates the pressure in the braking system. It is this piston that has the polymer seal on it that will fail over its lifetime; ultimately requiring this braking component to be replaced. The piston in the brake master cylinder can be seen by looking into the bottom center of this device. If the observer has another person depressing the brake pedal, they must be ready for the piston to force a fountain of fluid upwards. For this reason, care should be taken when observing the brake master cylinder when it is in action and the lid is off on your Honda vehicle. The smaller the fountain, the greater the leaking of the seal is occurring. It is possible to rebuild the Honda brake master cylinder but special tools and equipment will be required to properly perform this procedure. A majority of Honda owners just locate a rebuilt or new part at a trusted online auto parts store. This way the bad part is swapped out for the new component and the vehicle can be road worthily in a short amount of time once the brake system has been bled of air.