2 1/2 - Ton Series Trucks

Wheeled Vehicle Braking Systems
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6x6 trucks can be applied to the airhydraulic brakes of the 2 1/2

tonseries trucks. However, there is enough difference in the design

of the two brake systems so that a short discussion on the 2 1/2ton

truck brakes is needed.

The airhydraulic cylinder of a 2 1/2ton truck looks different from

that of a 5ton truck, but the operation is about the same. Brake

fluid applied pressure from the master cylinder is transmitted to the

slave cylinder and the fluid passage at one end of the hydraulic

control valve piston. The control valve piston then pushes on the

slave cylinder compensator piston moving it to close the air exhaust

valve and open the air inlet valve. Air pressure from the reservoir

flows through the air inlet opening and out one control line to the

power cylinder and a second control line to the trailer service

coupling.

Air pressure on the compensator piston and hydraulic pressure on the

control valve piston oppose each other to regulate the controlled air

pressure. When the brake pedal is released, hydraulic pressure is

removed from the control valve piston and the compensator piston

spring returns the compensator piston and control valve to the

released position. This allows the air inlet valve to close and

opens the air exhaust valve. Controlled pressure is exhausted

through the hollow compensator piston and out the air breather port.

The power cylinder and hydraulic slave cylinder work just like the

power and slave cylinders on the 5ton truck with two exceptions.

The hydraulic piston is returned by inner and outer slave cylinder

piston springs. There is no residual line pressure check valve in

the outlet of the 2 1/2ton truck's slave cylinder like on the 5ton

truck. The 2 1/2ton M35series truck has the residual line pressure

check valve in the outlet of the master cylinder.

The M35series cargo trucks do not have a hand control valve or

trailer couplings at the front of the truck as the 5ton truck does.

However, they do have service and emergency trailer couplings at the

rear of the truck. The 2 1/2ton tractor trucks have a hand control

valve so the trailer brakes can be operated separately.