Hydraulic System Components Automotive Service Technician Hydraulic System Components

Hydraulic system Components Include: Brake Fluid Master cylinder Brake Lines Valves (to control and time braking action) Flex Hoses Caliper Wheel Cylinders Figure 1 - Complete brake system showing relative locations of typical system components.

Warning: Brake Fluid Dissolves vehicle Paint! Handle with care! Brake fluid: Hydraulic fluid for brake function. Be sure to have the correct Department of Transportation (DOT) rating of fluid on the bottle. DOT 3 and 4 are the most common. A vehicles brake fluid is detrimental to the proper operation of hydraulic brakes. The proper fluid type and cleanliness are an important part of a technicians knowledge. Warning: Brake Fluid Dissolves vehicle Paint! Handle with care!

Figure 2 - A typical single piston master cylinder. The master cylinder is the beginning of the hydraulic system, which is activated via the drivers brake pedal Figure 2 - A typical single piston master cylinder. Master cylinder builds hydraulic pressure by trapping brake fluid from the reservoir in front of the piston and sealing cup as the brake pedal is depressed.

while keeping atmospheric pressure on the fluid. The Rubber Seal/bellow allows for continuous pressure to be placed on the fluid, preventing the chance of a vacuum to build inside the master cylinder reservoir. Figure 3 - The folds in the bellows allow it to follow the level of the fluid while keeping atmospheric pressure on the fluid.

Figure 7 - Master cylinder in the applied position. Again, note the position of the primary seal in relation to the vent port.

fluid bypasses the primary cup seal. When the piston releases faster than fluid can return through the lines, to prevent braking action from staying on, fluid bypasses the primary cup seal.

the entire hydraulic system remains at atmospheric pressure. Figure 9 - The vent port is exposed in the rest position, assuring that the entire hydraulic system remains at atmospheric pressure.

Figure 10 - Exploded view showing major parts of a tandem master cylinder.

Figure 11 - Front/rear split system typical of RWD and 4WD vehicles. To prevent complete brake failure, hydraulic circuits will be divided into two circuits: Figure 11 - Front/rear split system typical of RWD and 4WD vehicles.

Figure 12 - A typical diagonal split system.

Figure 17 - Tandem master cylinder in the fully released position. Majority of master cylinders on late model vehicles have tandem pistons – Why might this be? Figure 17 - Tandem master cylinder in the fully released position. Note that the primary cup on each piston is located slightly rearward of their vent ports.

Wheel Cylinder (drum brakes) Components consist of: Piston Piston cups Return spring Dust Boot

Figure 28 - Cup expanders maintain pressure on the lips of the cup seal, keeping air, dirt and moisture out of the system.

Figure 29 - Double ended wheel cylinder

This aids in bleeding air from the system. The bleed screw is usually positioned to be the highest point on the cylinder. This aids in bleeding air from the system.

Figure 32 - Pressure generated in the master cylinder is converted by the wheel cylinders to mechanical force to apply the brake shoes.

Figure 33 - Typical disc brake caliper assembly.

Caliper Pistons – A phenolic piston (left) and a steel piston (right).

Caliper Components consist of: Piston Piston Seal Dust Boot Slider bushings All rubber components must be protected from contact with greases, oils, and other petroleum-based products. Use and approved silicone brake lubricant.

Note the internal drillings connecting the bores. Figure 37 - Multiple piston calipers receive equal pressure on all pistons. Note the internal drillings connecting the bores.

Figure 38 - Fixed caliper halves showing the O-ring seal and drilled passages.

Figure 39 - Fixed caliper.

Figure 40 - Caliper piston seal flexes in its groove, making it act like a return spring for the pads to provide running clearance.

Figure 42 - Floating caliper.

Figure 45 - Two hoses such as this are used to connect the rear wheels to the brake system while still allowing suspension travel.

Figure 63 - These pictures show conditions that would warrant overhaul or replacement of the master cylinder.

Figure 68 - The bleeder screw seals at the bottom of its bore, which is also where it usually seizes. The fluid passage in the middle of the screw reduces its strength, making it easy to twist off.

Figure 69 - Check phenolic pistons carefully; they are very brittle and easily damaged.

Figure 70 - The hatched areas indicate where lubrication is required to assure that the caliper can slide freely on its mounting pins. Service every time the brake are replaced!

Lubricants Lubricants are an important part of keeping your brakes working safe. Proper use of high quality lubricants will ensure proper brake pad wear and long brake caliper life. Anti-seize: Prevents corrosion build up on mating parts Silicone brake grease: used for caliper pins on caliper that float and move. High temperature squeal reduction silicone: Adhesive silicone to damped brake squeal on vehicles that have a problem with squeal noise. 4 of 5

Figure 71 - Both of these cylinder cups were the same size before the one on the left was exposed to power steering oil.

Figure 76 - Some of the conditions to look for when inspecting flex hoses: cracks in the outer casing (left), internal leaks in the hose indicated by the staining (middle) and blister (right).