GMC 4000 Series Service Manual page 254

year periods, whichever occurs first (also depend­
ent upon type of operation and operators experience).
2. Clean all metal parts thoroughly, using a
suitable cleaning fluid. Blow dry with air or wipe
dry with cloth.
3. Inspect piston cap for signs of damage or
excessive wear. Piston should slide freely inside
cap assembly. Replace piston if badly worn or
damaged.
4. Inspect inside walls of cap assembly for
scratches, scores, or excessive wear. Slightly worn
spots may be removed with crocus cloth. Inspect
external threads on cap for rust or corrosion.
5. Inspect piston seal for cracking or deter­
ioration. Inspect expander and expander retaining
plate for deterioration. Replace piston assembly,
if necessary.
. Inspect pressure housing for scratches,
6
scores, or excessive wear. Examine all parts for
obstructions and remove any foreign matter.
7. Examine spring in cap for deterioration or
rust. Inspect release bolt for signs of rust on the
threaded portion. Unless spring or bolt is in very
bad condition, replacement should not be necessary.
See "Caution" in Step 10 of "Removal and D isas­
sembly."
. Discard O-ring and rubber washer. Replace
8
with new parts.
9. Examine diaphragm plate rod boot (in non­
pressure housing) for deterioration or cracks. If
deterioration or other damage is evident, replace
as follows:
a. Pull diaphragm plate rod, wedge rod guide
and boot out of wedge rod and mounting tube re­
spectively.
b. Remove guide and boot from diaphragm
G M C S E R V I C E M A N U A L
Figure 4 4 — Rem oving Pressure Housing with "Strap" Wrench
plate rod and install new boot on plate rod. Replace
wedge rod guide.
c. Apply a liberal amount of rubber cement to
boot flange and mating surface on non-pressure
housing.
d. Position plate rod on wedge rod and hold
rubber boot flange tightly against housing surface.
Flange should seal tight to keep any moisture or
foreign matter from falling into actuation com­
ponents.
NOTE: Be careful not to disturb wedge and
roller mechanism inside actuation housing when
repositioning plate rod on wedge rod.
BRAKE CHAMBER ASSEMBLY
AND INSTALLATION
Refer to figure 40 (also refer to figure 41 for
components).
1. Install O-ring in groove in pressure housing.
2. Install piston assembly in cap assembly.
3. Position rubber washer in pressure housing
at bottom of internal threads. Thread cap and
spring assembly into pressure housing and tighten
firmly against rubber washer. This may be done
with "strap" type wrench (see figures 44 and 45)
Sec. 5B
Page 247
AIR BRAKES