freightliner 108SD 2021, Driver Manual

Page: 124 / 191

2.4 When proper adjustment is obtained,
tighten the adjusting screw locknut, and
install the top cover. The pressure range
between cut-in and cut-out is not adjust-
able.
Cut-In Position
Apply soap solution around the cover and to the ex-
haust port. Slight bubble leakage is permitted. Exces-
sive leakage indicates a faulty inlet valve or faulty
lower piston O-ring.
Cut-Out Position
Apply soap solution around the cover and to the ex-
haust port. Slight bubble leakage is permitted. Exces-
sive leakage indicates a faulty exhaust valve seat,
exhaust stem O-ring, or O-ring at the top of the
piston.
If the governor does not function as described, or if
leakage is excessive, it is recommended that it be
replaced with a new or remanufactured unit, or re-
paired with genuine Bendix parts.
42–04 Air Dryer Check
The information in this MOP applies to Bendix AD-9,
AD-IP, and AD-IS/DRM air dryers.
IMPORTANT: Review the warranty policy before
performing any intrusive maintenance proce-
dures. An extended-warranty may be voided if
intrusive maintenance is performed during this
period.
Because no two vehicles operate under identical
conditions, maintenance and maintenance intervals
will vary. Experience is a valuable guide in determin-
ing the best maintenance interval for any one particu-
lar operation.
Every 900 operating hours, or 25,000 miles (40 225
km), or 3 months:
1. Check for moisture in the air brake system by
opening reservoir drain valves and checking for
the presence of water. If moisture is present, the
desiccant cartridge may require replacement;
however, the following conditions can also cause
water accumulation and should be considered
before replacing the desiccant:
1.1 An outside air source has been used to
charge the system. This air did not pass
through the drying bed.
1.2 Air usage is exceptionally high and not
normal. This may be due to high air sys-
tem leakage.
1.3 In areas where more than a 30-degree
range of temperature occurs in one day,
small amounts of water can temporarily
accumulate in the air brake system due to
condensation. Under these conditions, the
presence of small amounts of moisture is
normal.
NOTE: A small amount of oil in the system is
normal and should not be considered as a rea-
son to replace the desiccant cartridge. Some oil
at the dryer exhaust is normal.
2. Visually check for physical damage such as
chaffed or broken air and electrical lines and bro-
ken or missing parts.
3. Check mounting bolts for tightness. Tighten 30 to
35 lbf·ft (41 to 47 N·m).
4. Perform the operational and leakage tests listed
below.
Operational and Leakage Tests
1. Check all lines and fittings leading to and from
the air dryer for leakage and integrity. Repair any
leaks found.
2. Build system pressure to governor cutout, and
note that the dryer purges with an audible es-
cape of air. Watch the system pressure and note
the pressure fall-off for a 10-minute period. If the
pressure drop exceeds 1 psi/minute from either
service reservoir for a single vehicle; or 3
psi/minute for a tractor trailer, inspect the vehicle
air systems for sources of leakage, and repair
them. Refer to troubleshooting information in
Bendix service literature.
3. Check for excessive leakage around the purge
valve with the compressor in the loaded mode
(compressing air). Apply a soap solution to the
purge valve exhaust port and observe that leak-
age does not exceed a 1-inch (25-mm) bubble in
1 second. If the leakage exceeds the maximum
specified, refer to troubleshooting information in
the Bendix service literature.
Brakes
42
108SD and 114SD Maintenance Manual, October 2019
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