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|  MIL-B-62152A(AT)
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3.3.2 Braking. The service brakes shall control and hold the vehicle when loaded to its
specified GVW, on a 30 percent grade. Under all conditions of loading, the service brake shall
stop the bus, from a speed of 20 mph, within a distance of 30 feet from the point at which
movement of the brake pedal begins. Deceleration and stopping distance shall be demonstrated
on dry, hard, approximately level road surface that is free from loose material.
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3.3.2.1 Downhill braking. The vehicle braking system shall include at least one of the
following features:
(a) Brakes with a total of not less than 1,930 square inches of effective brake area
(b) Automatic transmission with built-in hydraulic retarder
(c) An engine type brake that brakes by engine compression through opening exhaust
valves near piston top center and venting to the atmosphere. The engine brake shall
include modulated control. The engine brake shall permit the bus loaded to GVW on
a dry, hard road surface to negotiate a six percent downgrade without exceeding
27 mph, within the operating restriction of the engine and transmission and without
the use of service brakes.
3.4 Chassis.
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3.4.1 Engine. The bus shall be furnished with a liquid cooled compression ignition,
two-stroke or four-stroke cycle diesel engine. The engine shall have not less than six cylinders.
The engine shall be the manufacturer's standard or optional engine for the commercial model
vehicle which meets or exceeds the requirements of this specification. The engine shall be
mounted at the rear or mid-mounted under the floor between the front and rear axles. An engine
governor set and sealed to limit the engine speed to the maximum recommended operating speed
shall be provided. An oil cooler shall be furnished. Engine net horsepower used in performance
prediction calculations shall be determined in accordance with SAE J816 or SAE J1349.
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3.4.1.1 Engine compartment. The engine compartment ventilation and design shall allow
operation without damage to engine, transmission and all components when the vehicle is
operated in ambient temperatures of up to 112F. Ready access to engine compartment shall be
provided for servicing and routine maintenance of engine and engine components. Hinged
engine compartment covers or doors shall be provided with a device to hold them open for
servicing and maintenance.
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