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Brakes 235
The “121” Brake Standard
This manual refers occasionally to “121”
brakes. Although some operators believe
“121” only applies to vehicles equipped
with anti-lock devices, the “121” standard
applies to all vehicles that are capable of
on-highway operation.
The “121” is a Federal requirement also
covering alterations or changes to parts or
systems related to the “121” standard once
the vehicle has been placed in service. The
owner and operator should be aware that it
is a violation for any repair facility to make
any part or component inoperative when it
is required for “121” compliance.
Charging Air To Another Vehicle
There are many methods which may be
used to charge the air system of another ve-
hicle. Vehicles equipped with the standard
two-valve system (trailer supply and
parking brake) must use the following pro-
cedure when using the emergency trailer air
line as an auxiliary air source, other than to
charge the trailer air reservoirs.
Before working on a vehicle, set the
parking brakes, place the transmission in
neutral, and block the wheels. Failure to
do so can result in unexpected vehicle
movement and can cause serious per-
sonal injury or death.
1 Connect the emergency trailer air line
to the auxiliary source.
2 Start the engine.