The brake master cylinder is the first point where hydraulic pressure is created, and transfers this force to the brakes through brake pipes and hoses. The pressure inside the cylinder is created by a piston inside which is pushed by the brake pedal (with assistance of the brake booster), and pushes the brake fluid.
The brake master cylinder is located on the firewall in front of the driver's seat (in exception of some American/European cars where they are left hand drive converted) and is mounted on the brake booster. It will have pipes that run off the cylinder and travel to either an ABS module or straight to the brake callipers.
Reasons for checking the brake master cylinder: this is a major component in the braking system, it could be responsible for a number of braking issues, including weak braking, loss of fluid (leaks), etc.
A typical construction design of a master cylinder will look like this, having a reservoir mounted to the top (where fluid is stored and topped up) and a push rod connected to a piston inside, which pushes the fluid to the proportioning valves, and eventually to the pipes.
The push rod is pushed by the brake pedal, it is leveraged to amplify the force of the foot. this is done by putting the push rod close to the pivot point and far from the pedal.
Inspecting the master cylinder:
Visually check all the parts, seals are not solidified or ripped, no pitting or denting on parts, no rust or residue on anything. Anything significant will show when bench testing the component.
Bench testing the Master Cylinder:
The main thing that we need to check in the master cylinder is that the cylinder is created/holding pressure. This means that any leaks will not be passed. The cylinder is mounted onto a vice grip, and the piston is pushed with a screwdriver (wearing safety glasses). The cylinder should hold pressure, this means it should not feel as though the piston is slowly moving in with the same amount of force being applied.
Bleeding brakes:
It is useful to use a different coloured brake fluid to the existing fluid in the system. This means that you can identify the fluid from old and new when you are bleeding the system. Make sure you don't keep the reservoir open for too long as the fluid absorbs moisture, and this can lower the quality of the fluid.
The push rod is pushed by the brake pedal, it is leveraged to amplify the force of the foot. this is done by putting the push rod close to the pivot point and far from the pedal.
Inspecting the master cylinder:
Visually check all the parts, seals are not solidified or ripped, no pitting or denting on parts, no rust or residue on anything. Anything significant will show when bench testing the component.
Bench testing the Master Cylinder:
The main thing that we need to check in the master cylinder is that the cylinder is created/holding pressure. This means that any leaks will not be passed. The cylinder is mounted onto a vice grip, and the piston is pushed with a screwdriver (wearing safety glasses). The cylinder should hold pressure, this means it should not feel as though the piston is slowly moving in with the same amount of force being applied.
Bleeding brakes:
It is useful to use a different coloured brake fluid to the existing fluid in the system. This means that you can identify the fluid from old and new when you are bleeding the system. Make sure you don't keep the reservoir open for too long as the fluid absorbs moisture, and this can lower the quality of the fluid.
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