284
Brakes
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” requirement also covers alter-
ations or changes to parts or systems
related to the “121” standard once the vehi-
cle has been placed in service. The owner
and operator should be aware that it is a vi-
olation 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.
