12M Series 3, 140M Series 3, 160M Series 3, 140, 150 and and 160 Motor Graders Service Brakes Caterpillar

Service Brakes
1.1. Compensator
2.1. Indicator
3.2. Hydraulic Oil Additive

Illustration 1g01312590
The guard has been removed for clarity.
(1) Oil inlet port
(2) Tandem housing
(3) Wheel spindle housing

Illustration 2g03487278
Typical Example
Section View
(3) Wheel spindle housing
(4) Cover
(5) Brake hub
(6) Shims
(7) Sprocket
(8) Plates
(9) Brake discs
(10) Piston
(11) Oil compartment
(12) Duo-Cone seal
(13) Wheel spindle
(14) Spring
(15) Indicator

Power from the differential flows through the drive chain to sprocket (7). Inside wheel spindle housing (3), the sprocket turns wheel spindle (13), brake hub (5), and brake discs (9). The drive wheels are connected to the wheel spindle.

The four disc type brakes are used for the service brake system. There is one disc type brake in each wheel spindle housing (3). The brakes are cooled through the oil in tandem housing (2). The service brakes are activated by pressurized oil from the brake control valve. There is a Duo-Cone seal (12) that is located between the wheel spindle (13) and the wheel spindle housing (3). The Duo-Cone seal will seal in the oil. The Duo-Cone seal will also keep out the dirt, the water, and the other contaminants.

Plates (8) are held in the stationary position by dowels located in the wheel spindle housing (3). Brake discs (9) are splined onto brake hub (5). The brake hub is splined onto wheel spindle (13).

Illustration 3g03521656
(16) Brake warning lamp

Illustration 4g03637806
(17) Service brake pedal
(18) Rod
(19) Brake control valve

The braking and the hydraulic fan pump sends oil to the control manifold. The control manifold contains valves that control the pressure in the brake system. The control manifold contains a pressure sensor that sends an electronic signal to the monitoring system. When the brake pressure is low, the monitoring system turns on a brake warning lamp (16).

When you depress the service brake pedal (17), a rod (18) actuates brake control valve (19). Then, the brake control valve (19) for the service brakes will send pressurized oil from the brake accumulators to the service brakes. The position of the pedal regulates the amount of oil pressure to the brakes.

Pressurized oil flows through oil inlet port (1) into oil compartment (11). Oil then moves piston (10) against plates (8) and brake discs (9). The piston pushes the discs against wheel spindle housing (3). As oil pressure increases, the piston is forced against the discs. This action will cause friction between the discs. As the friction increases, the brake discs (9), brake hub (5), and wheel spindle (13) will start to slow down, since the plates (8) and wheel spindle housing (3) cannot rotate. The brakes are in BRAKE ON position, but the brakes are not fully engaged.

If the operator continues to depress the pedal downward, oil pressure will increase in oil compartment (11). The friction between the discs will then become great enough to stop the brake discs (9), the brake hub (5), and the wheel spindle (13). Oil pressure is held in the brakes in order to keep the brakes in the BRAKE ON position.

When the operator releases the pedal, oil pressure in oil compartment (11) is released through oil inlet port (1) to the brake control valve (19). Then, springs (14) force piston (10) back to the BRAKE OFF position. Brake discs (9) are again free to turn between plates (8).


Illustration 5g03519482
(20) Locknut
(21) Compensator

Compensator (21) will compensate for brake wear by limiting the retract position of piston (10). The compensation is accomplished by adjusting compensator (21) to a depth that will allow piston (10) to retract only a given distance. When compensator (21) is properly adjusted, piston (10) will retract against compensator (21). Piston (10) will stroke a shorter distance as brake discs (9) continue to wear.

Reference: Refer to the Testing and Adjusting , "Brake Disc Wear - Check" for additional information concerning the Compensator.


Illustration 6g03519478
(15) Indicator
(22) Cover
(23) Surface

Indicator (15) will indicate the proper replacement interval for the brake. Indicator (21) is compared to surface (23) with the brakes fully applied.

  • (AA) Brakes have sufficient pad remaining. Surface (23) is between the end of the pin and the shoulder.

  • (BB) Brakes require replacement. The end of the pin of the indicator is flush or below surface (23).

  • (CC) Brakes are possibly warped. The shoulder of the pin protrudes beyond (23).

Hydraulic Oil Additive

The service brakes on this machine are designed for operation with a hydraulic oil additive in the tandem oil. This additive reduces brake noise and the additive also reduces grabbing of the brakes.

Reference: Refer to the Operation and Maintenance Manual, "Capacities Refill" or the Operation and Maintenance Manual, "Lubricant Viscosities" for information regarding the addition of this Hydraulic Oil Additive.

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