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|  MIL-T-62735
3.3.15.5 Service brake aid. When specified for diesel engine driven, class 32 and larger
vehicles (see 6.2), the service brakes shall have aid by one of the following systems:
(a) An electromagnetic driveshaft retarder
(b) A system which opens all or some of the engine exhaust valves near the end of the
compression stroke, converting vehicle motion to a pumping loss
(c) A controlled gate valve in the exhaust manifold, which produces back pressure on
the engine pistons during the exhaust stroke or
(d) As an additional option, when an automatic transmission is specified, a
hydrodynamic retarder integral with the transmission.
3.3.15.5.1 Service brake aid control. The system shall have a switch on the cab
instrument panel to activate, modulate, and cut out the service brake aid. The switch shall be
marked to indicate its position in accordance with 3.10.5. When active, system control shall be
by the conventional service brake foot control.
3.3.15.5.2 Brake aid performance. Each of the four systems shall provide the maximum
retardation commercially available by use of such a system on a vehicle of the class (GVW)
specified. For (b) and (c), above, the engine manufacturer shall approve the service brake aid
application.
3.3.16 Frame. When specified for class 66, 75 and 85 (see 6.2), the frame resisting
bending moment (RBM) shall be not less than that specified in table X. Otherwise, trucks with a
hydraulic crane or body dump mechanism or when specified (see 6.2) other types, shall have a
heavy duty frame or frame with reinforcements.
3.3.16.1 Heavy duty frame. The heavy duty frame shall have frame rails of greater
section modulus than the manufacturer's standard for the vehicle class and shall provide
structural strength at least equivalent to the reinforced frame specified herein.
3.3.16.2 Frame reinforcements. Reinforcements shall extend at least from the rear of the
front suspension, rear hanger bracket to the front of the rear spring, front hanger bracket
(for 4x2 and 4x4) or bogie trunnion mounting bracket (for 6x4, 6x6, 8x4 and 8x6).
Reinforcements for stake dump trucks and dump trucks shall provide sufficient structural
strength in the chassis frame, through increased RBM, to at least equal the loads imposed, with
the truck loaded to provide specified GVW. Frame reinforcements for trucks with a crane or
aerial device shall be in accordance with the crane or aerial device manufacturer's
recommendations.
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