it shall be possible to lock-up brakes with maximum application of the service brake pedal. All surfaces
shall be dry, clean, rough concrete with a frictional coefficient of 0.8.
A maximum of a 100 lbs foot pressure shall be required to lock brakes IAW SAE ARP
Braking capability shall be constant at any speed.
Physical arrangement of the tractor brakes shall allow brake/accelerator clearance for
heavy snow boots.
d. The master cylinder shall be the dual cylinder, dual reservoir type (tandem master
cylinder). Only two brakes shall have their fluid supplied per one side of the reservoir.
The parking brake shall be capable of holding the vehicle on a 25 percent
18.104.22.168.4 Parking Brake.
slope. Physical arrangement shall be such that at least 3 inches of clearance shall be provided for
operation by an operator wearing arctic gear.
Air for Trailer Towing. When specified (see 6.2), the tractor shall comply with DL690-1G-109
and DL690-1G-209 (basic configuration including air for trailer towing), DED 7 or an equivalent system
per SAE J318. When air for trailer towing is required, means shall be provided so the trailer brakes shall
be activated between 0.3 and 0.6 seconds before the tractor service brakes. When air for trailer towing is
required, tow additional glad hand quick connectors shall be located on the front of the vehicle and shall
comply with DL960-1G- 109 and SAE J318. All glad hand quick connectors shall have covers installed on
them. A minimum of 7 1/2 CFM of supplied air shall be supplied at a minimum of 110 psi and maximum
of 125 psi. Air shall be modulated, proportional between foot pressure applied and air released to the
Frame. Frame shall be properly designed, tested, and evaluated as to ensure that the frame's
load carrying capacity will be adequate to prevent any stress cracking, warping, etc. during the life of the
vehicle. Frame rails shall have a minimum section modulus of 8.0 in3 each. Frame rails and
crossmembers shall have a minimum yield strength of 36,000 psi. The frame assembly shall be bolted
and/or riveted; no welding shall be performed unless certification that the material has been properly
normalized (stress relieved) and its strength has not been degraded is provided with First Article Report.
Welded and brazed fabrication shall be in accordance with AWS D1.1 and all welders and welding
equipment shall be certified by the requirements of Section 5 of AWS D1.1. No unused holes shall be
permitted in the frame rails. There shall be no point on the frame that during static loading from the
maximum gross vehicle weight, exceeds 2070 (safety factor of 5) of the yield strength of the frame. At no
time during the operation described in paragraph 22.214.171.124 shall the frame stresses be greater than 50
percent of the material minimum yield strength (safety factor of two). Fatigue calculations from the
strain gauge testing of paragraphs 4.5.20 shall project a vehicle life as follows:
One thousand miles over test course (see 4.5.20. 1).
b. Ten thousand maximum brake stops.
Ten thousand miles under loads as tested (see 126.96.36.199).
3.3.5 S u s p e n s i o n . A four point spring with shock absorbers (hydraulically dampened) system with a
minimum of two inches of working travel must be provided. The system must provide a dynamically
stable ride in both longitudinal and lateral directions. The front and rear axle frequencies shall be such
that normal fore/aft pitch is minimized. The system must maintain four wheel contact with the normal
working surface. MIL-STD-1472, Human Engineering Design Criteria, shall establish the limits of
acceptable vibration, noise, shock and impact forces the driver is exposed to,