Introduction

Location of Components
(1) Master cylinder. (2) Service brake pedal. (3) Parking brake lever. (4) Parking brake. (5) Service brakes. (6) Brake drums.

The machine has two separate braking systems. The service brake is used to stop the machine during normal operation. The parking brake is used to hold a stopped or parked machine in place. The parking brake may also be used to stop the machine if the service brake fails to operate. Both braking systems have been designed and tested to be in accordance with SAE J1136 braking recommendations.

The service brake is hydraulically-operated using brake pedal (2). When the operator steps on the brake pedal, master cylinder (1) sends brake fluid to service brakes (5). There are four service brakes (5) and four rotating brake drums (6). These components are located on the rear drive wheels of the machine. Service brakes (5) apply braking force to brake drums (6), stopping the machine or holding it in position.

Parking brake (4) is part of the machine's power train. The parking brake drum is bolted to the transmission output flange. Lever (3) is mechanically connected to parking brake (4). When the operator pulls back on the lever, the parking brake is applied. When the operator pushes the lever down, the parking brake is released.

Brake Pedal

Brake Pedal
(1) Pivot bolt. (2) Clevis. (3) Push rod. (4) Spring. (5) Pedal.

The operator applies the service brake by pressing pedal (5). One end of push rod (3) is connected to the pedal through clevis (2). The other end of push rod (3) contacts the master cylinder piston.

When the operator presses on the pedal, the pedal pivots on bolt (1). This causes push rod (3) to move to the right. Movement of the push rod actuates the master cylinder piston.

When the operator releases pedal (5), spring (4) moves the pedal and the push rod back to their original positions.

Master Cylinder

Master Cylinder
(1) Cup. (2) Piston. (3) Reservoir. (4) Passage. (5) Cup. (6) Relief valve. (7) Check valve. (8) Port. (9) Spring. (10) Chamber. (11) Passages. (12) Piston. (13) Passage. (14) Spring. (15) Chamber. (16) Seat.

The master cylinder changes brake pedal force into hydraulic pressure. The master cylinder sends this hydraulic pressure to the service brakes to stop the machine.

The free end of the push rod (part of the brake pedal assembly) fits inside cup (1) at the left end of piston (2). The push rod is covered by a rubber boot to prevent dirt from entering the master cylinder.

Reservoir (3) and chambers (10) and (15) are filled with brake fluid all the time. When the operator presses on the brake pedal, the push rod moves piston (2) to the right. Piston (2) moves past passage (4), sealing off chambers (10) and (15) from reservoir (3).

Movement of piston (2) compresses springs (9) and (14). This causes piston (12) to move to the right, sealing against seat (16). As piston (2) moves further, pressure builds up in chamber (15). Fluid from chamber (15) moves through passages (11) and past the outside lip of cup (5) to chamber (10). This provides greater braking pressure with continued pedal movement.

Relief Valve
(17) Spring. (18) Piston. (19) Passage. (20) Passage. (21) Passage. (22) Seal. (23) Spring. (24) Passage.

Pressure in chambers (10) and (15) is equal until the pressure of the fluid reaches approximately 520 kPa (75 psi). This is the setting of relief valve (6). Fluid in chamber (15) is ported through passage (21) to piston (18). When the pressure of the brake fluid reaches 520 kPa (75 psi), piston (18) moves up against spring (17). Fluid from chamber (15) flows through passage (19) to reservoir (3).

When fluid in chamber (15) flows through relief valve (6), the pressure in chamber (15) becomes less than the pressure in chamber (10). This causes the lip of cup (5) to press against the inside surface of piston (2). This prevents fluid in chamber (10) from flowing to chamber (15).

As piston (2) moves further to the right, pressure in chamber (10) increases. Brake fluid under pressure is ported through passage (13), past check valve (7), to port (8). Brake fluid exits the master cylinder through port (8), and is routed through brake lines to the service brakes on the rear wheels of the machine.

When the operator releases the brake pedal, springs (9) and (14) move pistons (2) and (12) back to the left. Fluid in the brake lines flows back into the master cylinder through port (8). This fluid flows past check valve (7), into chambers (10) and (15). The two pistons (2) and (12) may move to the left faster than fluid can flow back through port (8). When this happens, seal (22) moves down against spring (23). Fluid in reservoir (3) flows through passages (20) and (24), keeping chambers (10) and (15) filled with fluid at all times. As fluid comes back from the brake lines, excess fluid flows through passage (4) back to reservoir (3).

Check valve (7) is used to keep some pressure in the brake lines when the brakes are released. Fluid pressure to the brakes will be approximately 100 kPa (15 psi) when the brakes are released. This low pressure helps prevent air from entering the brakes when the machine is at rest and requires less piston travel to apply the brakes.

Service Brake

Service Brake
(1) Block. (2) Piston. (3) Port. (4) Piston. (5) Block. (6) Return spring. (7) Return spring. (8) Shoe. (9) Shoe. (10) Shoe hold down pin. (11) Shoe hold down pin. (12) Automatic adjuster.

The four service brakes (two left brakes and two right brakes) receive hydraulic pressure from the master cylinder. Each brake changes this pressure into mechanical braking force to stop the machine.

The service brakes are secured to the lower drive housing, and do not rotate. Each service brake is located inside a brake drum. The brake drums are attached to the drive wheel axle shafts and rotate at the same speed as the drive wheels.

Brake fluid (under pressure from the master cylinder) enters the service brake through port (3). This causes piston (2) to move to the left, and piston (4) to move to the right. Piston movement causes blocks (1) and (5) to push against shoes (8) and (9).

The outside surface of shoes (8) and (9) is lined with a brake material. The shoes move outward into the brake drum. Shoe linings are forced against the inside of the drum. This applies the brake, preventing the drum and the drive wheels from turning.

When the operator releases the brakes, springs (6) and (7) pull shoes (8) and (9) away from the brake drum. Pistons (2) and (4) are forced back into the cylinder bore. Brake fluid exits the service brake through port (3), and is routed back to the master cylinder.

Shoe hold down pins (10) and (11) hold shoes (8) and (9) in the center of the brake drum. Automatic adjuster (12) adjusts the positions of the shoes during reverse braking. This maintains the correct distance between the shoes and the drum, providing a consistent braking ability as the shoes wear.

Parking Brake

Parking Brake
(1) Drum. (2) Band. (3) Cams. (4) Link. (5) Lever. (6) Bolt.

Introduction

Drum (1) is bolted to the transmission output flange at one end, and to the drive line at the other end. Whenever the machine is driving in forward or reverse, drum (1) rotates at transmission output speed. This sends power to the drive line, propelling the machine.

Reference: For information on the transmission and the drive line, see Power Train Systems Operation Testing and Adjusting, Form No. KENR2398.

Brake Released

To release the parking brake, the operator pushes lever (5) down, as illustrated. Link (4) moves to the left. Two cams (3) and bolt (6) are in the lowered position shown.

This expands the diameter of band (2), creating a little space around drum (1).

When the machine is moving, drum (1) can rotate freely, transmitting torque from the transmission to the drive line.

Brake Applied

To apply the parking brake, the operator pulls lever (5) up. Link (4) moves to the right. Two cams (3) pivot upward, raising bolt (6). This closes the diameter of band (2). Friction material on the inside of band (2) tightens around drum (1), applying the brake. Drum (1) is held stationary. This prevents the transmission output flange from rotating, holding the machine in a stationary position.