GMC 4000 Series Service Manual page 180

7. If necessary, adjust the brake pedal free-
play as directed.
8. Connect battery ground strap or stop light
wires and brake warning switch wire (whichever
was disconnected at removal).
9. Test brakes and make any necessary ad­
justments if operation is not satisfactory.
MASTER CYLINDER OVERHAUL
The following procedures cover disassembly,
cleaning, inspection and repair, and assembly of
components used in both the brake and clutch cyl­
inder bores on double barrel master cylinders and
on brake cylinder bores on single barrel cylinders.
The m a ste r cylin d er a sse m b ly u sed w ith dash
mounted power booster is integral with the booster
and has a different internal construction. They can
be removed and installed on the vehicle as des­
cribed in "Master Cylinder Replacement." Over­
haul of this type master cylinder is covered in the
unit overhaul manual as part of the complete a s­
sembly overhaul.
OVERHAUL (EXCEPT SPLIT-TYPE)
(Refer to Figure 12)
1. Clean all dirt from outside of unit, using a
non-petroleum solvent.
2. Remove snap ring from groove in both cyl­
inder bores.
3. Remove piston assembly, primary cup,
return spring and retainer assembly, check valve
and check valve seat from brake cylinder bore.
4. Remove piston assem bly, primary cup, and
return spring and retainer assembly from clutch
cylinder bore.
5. Remove cover from cylinder housing.
6. Remove bleeder screw (if used).
Cleaning
Immerse all parts in denatured alcohol and
wash thoroughly. Wipe sm all parts dry and blow
out inside of reservoir and cylinder bores. Make
sure intake and by-pass ports in cylinder housing
and bleeder holes in piston are clean.
CAUTION: DO NOT use kerosene or
gasoline for cleaning master cylinder
components.
Inspection and Repair
Master cylinder repair kits are available
which contain all the parts ordinarily required
when overhauling master cylinders. Refer to ap­
plicable Parts Book for part number of repair kit.
In addition to replacement of parts contained in
repair kit, master cylinder should be inspected
and repaired, if necessary, as follows:
G M C S E R V I C E M A N U A L
ed, recondition by honing. Be sure to use proper
size hone. (Refer to "Specifications" for nominal
diameter of cylinder bores.) Do not hone more than
necessary to remove scores and smooth up cylin­
der. Remove burrs caused by honing from around
by-pass and intake ports.
between piston and cylinder wall should be within
0.001" to 0.005" when checked with feeler gauge.
Assembly (Fig. 12)
bores and dip all internal parts in hydraulic brake
fluid.
of double barrel cylinders as follows:
then position check valve on seat.
in bore with large diameter end of spring over
check valve.
lip of cup toward outlet end. Make sure end of re­
turn spring seats inside the cup.
into cylinder bore, with open end of piston toward
open end of cylinder.
ing spring, and install snap ring in groove in bore.
Make sure snap ring is fully seated in groove.
as follows:
cylinder bore, large diameter end first.
lip of cup toward outlet end. Make sure end of
spring seats inside the cup.
der bore, with open end of piston toward open end
of cylinder.
ing spring, and install snap ring in groove in bore.
Make sure snap ring is fully seated in groove.
OVERHAUL (SPLIT-TYPE)
Disassembly (Refer to Fig. 13)
Pour out any excess fluid and stroke piston to
force fluid through outlet ports.
bottom of reservoir housing.
ring from groove in end of cylinder bore.
HYDRAULIC BRAKES
1. Examine cylinder bores. If scored or rust­
2. Check piston fit in cylinder bore. Clearance
1. Before assembling, coat inside of cylinder
2.
In sta ll com ponents in brake cylin d er b ore
a. Install check valve seat in cylinder bore,
b. Install return spring (shortest of the two)
c. Install primary cup in cylinder bore with
d. Insert piston and secondary cup assembly
e. P ress piston into cylinder bore, com press­
3. Install components in clutch cylinder bore
a. Install return spring (longest of the two) in
b. Install primary cup in cylinder bore with
c. Insert piston and secondary cup into cylin­
d. P ress piston into cylinder bore, com press­
4. Install cover on cylinder reservoir.
5. Install bleeder screw (if used).
1. Remove cylinder cover bolt and gasket.
2. Lift off reservoir cover and cover seal.
3. Remove piston stop bolt and gasket from
4. Use snap ring pliers and remove retainer
Sec. 5A
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