Chevrolet 10 Series 1968, Service Manual

Page: 344 / 713

BRAKES 5-101
TRAILER EQUIPMENT DD2
IN D EX
GENERAL DESCRIPTION
The 1968 T railer Emergency A ir Brake equipment is
available on all CA-MA models in the 60 Series, in­
cluding base and RPO axles. When trailer brake option
is used with Emergency A ir Brakes, all added safety
features incorporated in foregoing DD2 system, also
govern the trailer brakes.
The Emergency A ir Brake and Tra iler Brake combina­
tion primarily consist of, over and above those covered
under base DD2 system, the following components. A
new Trailer A ir Brake Emergency Shut Off Valve is also
incorporated this year, thereby simplifying the installa­
tion. See Figure 147-148.
TRAILER EMERGENCY VALVE (Fig. 149)
System Checking and Leakage Tests
To make the following system checking and leakage
tests, an accurate test gauge installed in a spare hose
coupling is required. The vehicle dash gauge should be
checked for accuracy against the test gauge prior to
making these tests.
1. Block and/or hold the vehicle by a means other than
air brakes during these tests.
2. Drain vehicle primary reservoir supply, then close
drain cocks.
3. Connect assembled hose coupling and test gauge in
trailer emergency hose coupling. Start engine and
build up system pressure.
4. As primary reservoir pressure builds up there
should be no pressure reading on test gauge. When
system pressure reaches 30 to 40 psi range on dash
gauge make and hold a hand valve application and
observe that no air escapes at the open trailer
service hose coupling.
5. When system pressure reaches approximately 60
psi, the Tra iler Emergency Control Valve handle
should be pushed in. System pressure should show
at once on the test gauge connected in the emergency
line and the handle of the Valve should stay in auto­
matically.
6. Build system pressure up to vicinity of 100 psi., then
stop engine. With engine stopped, wait momentarily,
then notice that dash gauge and test gauge pressure
readings are equal. While still in this position,
make a hand valve application and observe that air
is delivered out the open trailer service coupling.
7. With the Tra iler Emergency handle still in, check
for leakage at exhaust and tripper exhaust ports.
Also, check Tractor Protection Valve exhaust and
open service coupling for leakage.
8. Pull handle out; pressure on test gauge connected in
the emergency line should drop to zero. With the
handle out, make and hold a hand valve application
and observe that no air is delivered at the open
trailer service coupling. While still holding the hand
valve application, check at the service hose coupling
for Tractor Protection inlet valve leakage. Release
hand valve application.
9. Push handle in and if necessary start engine and
F ig . 1 47-Traile r Emergency A ir Brake V a lv e s, Fittings and Pipes F ig . 1 48-Traile r Emergency A ir Brake System
PLUG
lwt
, r^SSURE
SWITCH ASSEMBLIES
MANUAL AND
EMERGENCY
CONTROL
VALVE
DOUBLE CHECK
VALVE AND
STOP LAMP
SWITCH
CHEVROLET TRUCK SERVICE MANUAL