Chevrolet 70 1969 Series, Shop Manual

Page: 230 / 913

BRAKES 5B-37
I.C.C. BRAKE SYSTEM EQUIPMENT
Some vehicles are equipped with special I.C .C .
(Interstate Commerce Commission) brake system
equipment in conjunction with the trailer brake
controls. These controls are a tractor protection
(breakaway) valve and a trailer emergency air
supply control valve. These controls are provided
for the following purposes:
1. They protect the tractor air system from
complete loss of air pressure in the event of a
trailer breakaway or loss of air pressure in the
trailer air system.
2. They automatically actuate the trailer brake
emergency relay valve (on trailer) in case the
tractor air system pressure falls below 45 psi.
3. They provide the driver with a manual
means of actuating the trailer brake emergency
relay valve (on trailer).
TRAILER BRAKE HAND
CONTROL VALVES
Three different trailer brake hand control
valves are used on these models. Midland-Ross
valve model N-3973-H is used on all tilt cab models.
The other two hand control valves are used op­
tionally on conventional cab models. Bendix-West-
inghouse (Model TC-2) and Midland-Ross (Model
N-30060) are completely interchangeable.
All three valves are mounted on the steering
column with the operating handle on the right-hand
side (see fig. 14). The valve graduates the deliver­
ed air pressure in proportion to the degree the
operating handle is moved. That is the farther the
handle is moved from "off" to "on," the greater
the air pressure delivered to the trailer brakes.
If, at any time during such an application, a service
brake application is also made with the foot-con­
trolled valve, whichever valve releases the greater
air pressure will control the brakes.
On Midland-Ross valve model N-30060 it is
necessary to hold the handle in the desired posi­
tion in order to apply trailer brakes. When handle
is released, it automatically returns to the "off"
position. The Bendix-Westinghouse valve (Model
TC-2) and the Midland-Ross valve on tilt cab
models (N-3973-H) will remain in the placed posi­
tion until manually moved. Other than this oper­
ation of all three valves is identical.
Trailer Brake Hand
Control Valve
Air Lines to
Application Valve
Application Valve
Stop Light Switch and
Double Check Valve
5 Line to Tractor
Protection Valve
6 Brake Pedal
7 Steering Column
Bracket
8 Steering Column
r-2195
Figure J 3— Trailer Brake H and Control Valve and Brake
Application Valve Installed IConv. Models)
4. Remove bolts attaching mounting bracket
and valve to steering column.
5. Remove valve and bracket.
H A N D C O N T R O L V A L V E R E P L A C E M E N T
Removal
1. Block vehicle wheels.
2. Drain air from brake system.
3. Disconnect air lines from valve.
Installation
1. Position valve and mounting bracket on
steering column. Fasten with bolts.
2. Connect air lines to valve.
3. Start engine and build up air pressure.
4. Check for leaks and operation of brakes.
CHEVROLET SERIES 70 -80 H EAVY DUTY TRUCK SH O P M A N U A L