PARKING BRAKE APPLICATION

Fig. 1 - Double Diaphragm Spring rake Chamber

TM-5-3820-256-24-4 Drilling System Well Rotary Truck Mounted Air Transportable 600 Feet Capacity Model LP-12 NSN 3820-01-246-4276 Manual
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SERVICE MANUAL PARKING BRAKE APPLICATION To apply the spring (parking) brake, the operator of the vehicle positions the control valve in the applied position which exhausts air pressure from the spring brake loaded chamber (Fig. 4). Upon reduction of air pressure in the chambers, the parking brake springs will apply the rear brakes through the spring brake pushrod and service brake pushrod assemblies which are in turn connected to brake slack adjusters or brake wedge assemblies. Fig. 4 - Parking Brake Application To release the parking brake, the operator positions the control valve to the released position which actually applies air in the spring brake system, thereby loading the chambers, and air pressure overcomes the heavy springs forcing the spring brake pushrod and diaphragms to released position or normal driving position (Fig. 2). Upon loss of air pressure or reduction of air pressure in the vehicle air system, the spring (parking) brakes will automatically apply, providing an emergency brake. Refer to Air Brake System (FMVSS-121) section that applies to your vehicle for complete detailed instructions pertaining to the operation of the "air system" in the event loss of air is ever encountered. MANUAL RELEASE OF SPRING BRAKE To release the spring brake (manual release) in the event there is loss of air and the vehicle must be towed or whenever the spring brake chamber assembly is removed from the vehicle, the spring brake must be manually released or "caged" (Fig. 5). Fig. 5 - Spring Brake In Manual RIoas4ed Position To manually release the spring brake chamber you are actually compressing the spring to relieve any tension on the pushrod assembly. WARNING Before manually releasing the spring brakes, be sure to block the wheels so that the vehicle cannot move when the brakes are released. For towing, make sure the vehicle is connected or secured to tow vehicle before releasing the spring brakes. The spring brake chamber can be manually released (caged) in two manners. If the vehicle has 586 kPa (85 psi) of air or more, manually releasing the spring brakes can be accomplished easier with air in parking brake system if the breather cap is removed and the release bolt backed off counterclockwise as follows: Type 24 and 30 chambers 57 to 64 rwm (2-1/4 to 2-1/2") Type 36 chambers 70 to 76 mm (2-3/4 to 3"). CTS-4101W - Page 4

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