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 6-136.
REPAIR.
6-140. INSPECTION AND REPAIR.
Proceed as
follows (figure 7-29).
(1) If linings on brake shoes are worn to less
(1) Remove filler cap and gasket from
than 1/16-inch at the thinnest point, install new bonded
cylinder (32) and discard fluid in reservoir.
linings. Install linings in accordance with good practice
(2) Pull push rod (34) free of bellows (33) and
and instructions for use of equipment available.
remove bellows.
(3) Remove retaining ring and withdraw
(2) Repair
minor
thread
damage
(if
piston stop, piston, primary cup, spring, and check
practicable) with tap or thread chaser.
valve, from inside bore of body.
(4) Inspect all rubber parts for swelling,
(3)
Replace all distorted or damaged parts.
distortion or wear. Check that edges of primary cup,
6-137.
ASSEMBLY.
and secondary cup on piston are sharp and not flared.
NOTE
(1) Install wheel cylinder assembly on
If either cup shows any sign of damage, install
backing plates with spacer (42, figure 7-35), bolts (35)
the complete master cylinder repair parts kit.
and washers (36).
(5) Inspect bore of master cylinder for
scratches, rust spots or pitting. Remove minor surface
(2) Place brake shoes on backing plate studs
defects with a brake cylinder hone.
and install return springs and retaining springs with
brake service tools.
(6) Inspect check valve for cleanliness, firm
spring action, and tight sealing when closed.
(3) Install backing plates (43) on axle
housings and secure with screws (49) and washers (50).
(7) Probe ports visible through reservoir fill
hole with fine wire to be sure they are clean. If
(4) Connect brake tubings (15) to adapters
necessary to flush reservoir, use only pure denatured
(19) in wheel cylinders.
alcohol.
(5) Adjust brake shoes for proper shoe to
(8) Install check valve in bore of cylinder, to
brake drum clearance (para 6-36).
bottom, followed by spring, primary cup, piston and
piston stop.
6-138. WHEEL CYLINDER REPAIR. Proceed as
follows:
(9)
Install retaining ring to hold these parts in
(1) Remove rubber boots (37) from ends of
place.
wheel cylinder.
(10) Slide push rod into small end of bellows,
(2) Remove pistons (38), cups (39) and
then install bellows on master cylinder. If unit is not to
spring (40) from wheel cylinder.
be installed immediately, cap or plug all openings to
keep out dirt.
(3) Clean metal parts in alcohol. Wipe rubber
parts with clean soft lint-free cloth.
6-141.
TIRE REPLACEMENT.
(4) Inspect bore in cylinder and pistons for
6-142 GENERAL. Replacement of tires is usually
scoring or pitting.
made by pressing off old tire simultaneously with
pressing on new tire. Force required to replace a tire is
(5) Remove minor pitting or scoring by
5,000 pounds for each inch of wheel diameter. For
honing.
If piston or cylinder cannot be made
example, a tire used on a wheel 18 inches in diameter
serviceable by honing, replace entire wheel cylinder
requires 18 x 5,000 pounds or 90,000 pounds (45 tons)
assembly.
press capacity.
(6) Discard parts for which new parts are
6-143. TIRE
REPLACEMENT
PROCEDURE.
supplied in wheel cylinder repair kit.
Proceed as follows:
(1) Remove wheel from truck.
(7) Insert spring (40), cups (39) and pistons
(2) Support felloe of wheel with a ring slightly
(38) into bore in wheel cylinder.
smaller in diameter than wheel felloe and at least as
wide as tire to be pressed off.
(8)
Snap boots (37) onto ends of wheel
(3) Place new tire over old and center
cylinder.
carefully.
(4) Slowly lower press ram, check alignment, and
(9)
Install wheel cylinders on truck.
proceed with pressing operation.
6-139.
MASTER CYLINDER.
6-36
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