BRAKES-PARKING MOTOR TRUCK SERVICE MANUAL
Examine service brake diaphragm. Replace if worn,
brake chamber. Start at a 40 degree angle and work into
damaged or over one year old.
a vertical position as the piston and seal enter the
REASSEMBLY
chamber. NOTE: Do not use force, damage to the
1. Position piston assembly, spring and head in a
"feather edge" of the seal may result. If directions are
press as shown in Fig. 16. Thread release bolt
followed, the assembly will return to the case easily.
into piston so that bolt may be used to align
After piston is inserted, turn the complete assembly over
piston with bore in head, Fig. 19. Fold a small
and carefully guide the push rod through the push rod
square of emery cloth (abrasive side against
seal in the bottom of the chamber.
press and tool) to serve as a nonslip pad
7. Replace snap ring holding parking brake
between the press ram and tool, Fig. 14.
together.
CAUTION: Be certain that components are
8. To insure against water entering the chamber, a
aligned with press ram so that when pressure is
waterproof sealant (3M clear cement or
applied from press, spring does not "kickout".
equivalent such as windshield sealer) should be
Slowly compress assembly. Remove release
applied over the snap ring and snap ring groove.
bolt after pistbn is aligned with bore in head.
This is only required after the chamber has been
opened, because all new chambers are sealed.
Clean oil from all surfaces before applying
sealer.
9. Replace pressure plate on end of push rod, Fig.
10. It is recommended that after tightening the
screw, a lead BB or a piece of nonacid lead
solder be hammered into the screwdriver hole.
This will forestall service brake diaphragm
damage. Remove any slag so screw face is
perfectly smooth.
10. Inspect small air seal washer under release bolt.
If damaged, replace.
11. With washer on release bolt, screw release bolt
into piston about 3/4".
12. With parking brake unit on work bench, apply
approximately 60 psi of air to the spring brake air
inlet. Check for air leakage around the push rod
extending through the base. CAUTION: When
applying air pressure to brake chamber, always
Fig. 19 Aligning Piston with Head Bore.
keep brake chamber head (release bolt end)
pointed away from you. Never point the head
2. With assembly compressed, install guide washer
end towards you when chamber is charged with
and safety washer.
Tighten safety washer
air pressure.
(clockwise)
and
gradually
relax
press.
13. Release air pressure and pour approximately
CAUTION : Be certain safety washer is not
one ounce of light oil into opening in the end of
cross threaded.
Washer must be properly
the chamber. Allow oil to drain down into
installed and securely tightened to retain the
chamber.
1200 lbs. of spring pressure when press is
14. Replace diaphragm and set parking brake
relaxed.
assembly back on service brake chamber.
3. Lubricate push rod seal grooves with light oil.
Make sure the parking brake is not offcenter with
4. Saturate piston felt wiper with oil and replace into
the service brake chamber, then replace the
piston groove.
clamp ring.
5. Push the push rod back into the piston.
6. With cylinder on work bench, carefully replace
head spring piston assembly into
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