GMC 4000 Series Service Manual page 181

Sec. 5A
Page 174
HYDRAULIC BRAKES
1 Primary Piston Seal Cup
2 Primary Piston
3 Cover Seal
4 Reservoir Cover
5 Gasket
6 Cover Bolt
7 Intake Port
8 B y-P ass Port
9 Reservoir Housing
5. Remove stop plate.
6. All internal parts should slide easily out
of cylinder bore. If they do not, apply compressed
air carefully at front outlet port. If parts do not
remove easily, examine bore carefully for exten­
sive damage which may eliminate the possibility
of reconditioning the master cylinder.
Cleaning and Inspection
Clean all parts in denatured alcohol or brake
fluid. If reservoir housing is degreased, finish
clean to remove all trace of other solvents. Inspect
cylinder bore for scratches or corrosion. Minor
blem ishes can be removed with crocus cloth or a
clean-up hone. DO NOT OVERSIZE CYLINDER
MORE THAN 0.007-INCH OVER NOMINAL INSIDE
DIAMETER.
Check by-pass ports in both reservoirs to
make sure they are open and free of burrs. Probe
parts with soft copper wire 0.020-inchin diameter,
or sm aller. Do not use steel wire to check parts.
This may scratch bore of master cylinder or cause
burrs in port.
G M C S E R V I C E M A N U A L
10 Tube Seat
11 Secondary Piston Return
Spring
12 Secondary Piston Pressure
Cup
13 Floating Secondary Piston
14 Secondary Piston Seal Cup
15 Gasket
Figure 13— Split System Master Cylinder (S5500 - S6500)
16 Stop Bolt
17 Primary Return Spring
18 Primary Return Spring
19 Primary Piston Stop Pin
20 Primarv Piston Pressure
21 Stop Plate
22 Retainer Ring
Remove and discard all rubber parts. All rub­
ber parts are included in repair kit which is avail­
able from regular service parts sources.
Assembly (Refer to Fig. 13)
1. Coat all parts with a liberal amount of
brake fluid.
2. Install rubber seal cup on secondary piston
with cup lip facing rear (open end of cylinder).
NOTE: All other cup lips face opposite direc­
tion (closed end of cylinder).
3. Stack and install secondary piston spring,
pressure cup and piston in cylinder bore.
4. Install piston stop bolt and gasket, making
sure screw enters cylinder bore behind rear of
piston.
5. Assemble and install primary piston parts
in cylinder bore.
6. Install stop plate in cylinder bore.
7. Compress all parts in cylinder bore and
install retainer ring in groove.
8. Install reservoir cover and seal.
Retainer
Cup
-5245
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