GMC 4000 Series Service Manual page 168

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This group is divided into three sections as shown in Index below:
Section
5A
5B
5C
There are four different brake system s used
on vehicles covered by this manual.
1. Straight Hydraulic brakes are used as
standard equipment on all 4500 Series trucks.
2. Vacuum A ssisted Hydraulic brakes are
used as standard and/or optional equipment on
trucks covered by this manual as follows:
a. Dash mounted master cylinder with remote
mounted vacuum booster:
Standard - L4000, DL4000, S5500, and S6500
Series.
Optional - P4500 Model and L4000, DL4000
Series (Heavy Duty).
b. Dash mounted vacuum booster (with inte-
gral master cylinder):
Standard - E5500, 6500 Series.
Optional - E4500, E5500, 6500 Series
(Heavy Duty).
Subject
Brake System Maintenance
Brake Adjustments ................................ . . .
Bleeding B r a k e s ....................................... . . .
Brake Pedal and Linkage
Master Cylinders .................................... . . .
Wheel C y lin d e r s ....................................... . . .
Hydraulic L i n e s ....................................... . . .
Vacuum Power C y lin d e r s ..................... . . .
Vacuum Power Cylinder Air Cleaner . . . .
Vacuum Check Valve ............................ . . .
Vacuum Reserve Tank
Vacuum G a u g e .......................................... . . .
Vacuum P u m p ........................................... . . .
Air Power C y lin d e r ................................ . . .
Brake Shoes and Linings
Brake Shoe R e lin in g ................................ . . .
........................................... . . .
Brake Drums
G M C S E R V I C E M A N U A L
SECTION 5
Hydraulic B r a k e s ....................................................
Air Brakes ..............................................................
Parking Brake .......................................................
BRAKE SYSTEM EQUIPMENT
SECTION 5A
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Contents of this section are listed in Index below:
Page No.
.................. . . . 162
162
165
..................... . . . 167
170
175
179
180
181
183
......................... . . .
184
184
184
185
..................... . . . 187
199
199
Page No.
3. Air A ssisted Hydraulic brakes are used as
standard equipment on LA a.nd DLA 4000 Models.
4. Full Air brakes are available on all models
covered by this manual when specified on the sales
order or as optional equipment, except:
4500 Series and ES, SS5500 Models.
5. Optional Equipment is available in both
system s. Such item s as vacuum reserve tank,
heavy duty boosters, vacuum gauges, trailer brake
connections, air parking brake, moisture ejector,
etc., are factory installed options.
IMPORTANT: The following brake maintenance
schedules, adjustments, procedures, and replace-
ment techniques are required and are applicable
to normal vehicle usage. Unusual or severe oper-
ations require greater attention to the normal
maintenance approach commensurate with the us-
age severity.
GENERAL
The vacuum power assisted system used on
vehicles covered by this manual is described as a
"one to one" system; that is the volume of hydraulic
fluid output of the vacuum booster is the same as
the input volume. This type system eliminates the
need for compensating lines and also the need for
"pumping" the brake pedal in the event of loss of
vacuum power a ssist.
The vacuum system on these vehicles contains
a check valve which maintains enough vacuum in
the booster chamber to permit at least one power
assisted brake application after loss of vacuum
occurs.
The various components of the brake system,
such as shoe and lining assem blies, pedal and link­
age, power boosters, master cylinders, wheel cyl-
Sec. 5A
Page 161
161
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