 | |
| Illustration 1 | g00486149 |
Brake master cylinder (1) Outlet line to the brakes (2) Line (3) Internal reservoir (4) Piston for brake boost (5) Plunger (6) Inlet from the transmission hydraulic control (7) Plunger in the master cylinder (8) Valve (9) Outlet for the drain line to the center housing of the transmission (10) Inlet to the internal reservoir (11) Notch in the wall that divides the internal reservoir | |
 | |
| Illustration 2 | g00486182 |
Brake pedal | |
The service brakes are hydraulically power assisted. This brake boost is used in order to ensure positive braking that is equalized. Also, the brake boost provides quick response with minimal pedal effort.
The machines have one brake pedal. The brake pedal operates both the master cylinder and the brake boost.
The brake boost and the master cylinder are located on the bulkhead for the cab near the steering control.
The combination of the brake boost and the master cylinder ensures that only light pedal effort is required in order to operate the brakes.
The transmission hydraulic control supplies oil to the master cylinder through inlet (6). Internal reservoir (3) holds makeup oil for replenishing the brake system.
Plunger (5) pushes the piston for brake boost (4) while the brake pedal is depressed. Piston (4) begins to move to the left which moves plunger (7) .
The movement of plunger (7) causes the pressure to increase. This causes valve (8) to close. Oil is then forced from outlet (1) to the rear disc brakes.
When the brake pedal is depressed, oil flows through inlet (6) and around plunger (7). The oil then flows through inlet (10) to the internal reservoir (3). The static portion of the reservoir is filled when the oil level is high enough to flow over the notch in the dividing wall (11) .
Excess oil drains through outlet (9) to the rear housing for the transmission.
Brakes Released
 | |
| Illustration 3 | g00486290 |
Brake valve (1) Outlet line to the brakes (3) Internal reservoir (4) Piston for brake boost (6) Inlet from the transmission hydraulic control (9) Outlet for the drain line to the rear housing of the transmission (12) Rear seal (13) Inner seal (14) Spring (15) Center valve seal (EE) Charge oil (LL) Tank oil | |
When the brakes are released, charge oil is prevented from entering through inlet (6) for the brake boost.
Spring (14) keeps piston (4) for brake boost shifted to the right.
Rear seal (12) in piston (4) blocks inlet (6) from the charge oil.
Inner seal (13) is installed on piston (4) in order to ensure the proper alignment and smooth operation of piston (4) .
Center valve seal (15) is unseated. This allows flow from outlet port (1) to flow through the end port of the brake valve to reservoir (3). Next, the oil flows to the tank through outlet (9) .
Start of Brake Application
 | |
| Illustration 4 | g00486460 |
Brake valve (3) Internal reservoir (4) Piston for brake boost (5) Plunger (6) Inlet from the transmission hydraulic control (7) Plunger in the master cylinder (9) Outlet for the drain line to the center housing of the transmission (15) Center valve seal (16) Pushrod (17) Flapper valve (BB) Reduced high pressure oil (EE) Charge oil (LL) Tank oil | |
At the start of the brake application, pushrod (16) moves to the left. Pushrod (16) then contacts plunger (5). Pushrod (16) is connected to the brake pedal. Plunger (5) moves piston (4) for the brake boost to the left. This opens inlet (6) to the charge oil.
Charge oil fills the chamber behind piston (4) which closes flapper valve (17). Pressure that is behind piston (4) forces piston (4) to the left. Piston (4) then contacts plunger (7) in the master cylinder.
The pressure that is applied to piston (4) is proportional to the effort that is applied to the brake pedal. Boost pressure is controlled by the amount of leakage that is between the following two items: tip of plunger (5) and oil hole in the center of piston (4) .
The metal to metal contact between plunger (5) and piston (4) is increased as the brake pedal effort increases. As the contact increases, less charge oil leaks through the oil hole to reservoir (3) .
The low pressure oil on the left side of piston (4) is forced into reservoir (3). When the oil in reservoir (3) has reached the maximum level, oil is returned to drain (9) through the overflow passage in reservoir (3) .
If the brake application is made quickly, the fill time for the chamber which is behind piston (4) is too slow. This causes flapper valve (17) to remain open.
Flapper valve (17) allows oil from the low pressure side of piston (4) to flow through piston (4). This occurs until the boost pressure on the right side of piston (4) increases enough in order to close flapper valve (17) .
Flapper valve (17) ensures that the right side of piston (4) is always full. This provides a smooth brake pedal effort.
As the brakes are applied, pushrod (16) moves the following items to the left: plunger (5), piston (4) and plunger in the master cylinder (7). Oil that is compressed in the master cylinder moves center valve seal (15) over the end port. This closes off the inlet from reservoir (3) .
Reduced high pressure oil in the master cylinder begins to increase.
Brake Application
 | |
| Illustration 5 | g00486635 |
Brake valve (1) Outlet line to the brakes (3) Internal reservoir (4) Piston for brake boost (5) Plunger (7) Plunger in the master cylinder (15) Center valve seal (16) Pushrod (AA) High pressure oil (EE) Charge oil (LL) Tank oil | |
When the brakes are applied, pushrod (16) has moved the following items to the left: plunger (5), piston (4) and plunger in the master cylinder (7) .
Oil that is compressed in the master cylinder moves center valve seal (15) over the end port. This closes off the inlet from reservoir (3) .
As the plunger in the master cylinder (7) moves to the left, the increased pressure is applied to the brakes through outlet port (1) .
When the engine is off, the brakes will still function. However, no charge pressure is available to provide brake boost. The pressure that is applied to the plunger in the master cylinder (7) is directly related to the brake pedal effort.
When the brake pedal is initially released, the spring that is on the brake pedal pulls pushrod (16) to the right. Boost pressure moves plunger (5) to the right.
Charge oil flows through the oil hole in the center of piston (4). This fills both the low pressure side of piston (4) and reservoir (3) .