1999 GMC C-SERIES air suspension

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2-19 Air Shift Control
(Manual Transmissions Only)
The lever for the rear axle
shift control is either at the
lower right corner of the
instrument panel or on the
shift lever.
When the lever is moved to HI, the rear axle will be in
the high range. Switch it to LOW to get the low range.
The two
-speed axle should be in LOW when you park
the vehicle.
You'll need to engage the transmission, even moving the
vehicle a little, to be sure the axle is in the low range.
Then apply the parking brake, shift into NEUTRAL and
shut off the engine.Also, always start the vehicle in motion with the
two
-speed axle in the LOW position. When you upshift
the rear axle from LOW to HI, move the lever to the
HI position, disengage the clutch, pause, engage the
clutch and then press down on the accelerator. When
you shift the axle down from HI to LOW, you don't
have to clutch. Just move the lever to LOW, release the
accelerator and then quickly press it down again.
Air Suspension (If Equipped)
Your vehicle may be equipped with the Hendrickson
HAS Series single
-axle air suspension which is designed
for single
-axle on-highway use. This feature is available
in the 19,000 lb. capacity and as a low profile option for
operations which require extra cubic capacity and a
reduced deck height.
With this air suspension system, the ride height is set
during vehicle assembly so that the vehicle has a constant
frame height. The system will then increase or decrease
air pressure in the air springs to maintain this height.
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2-20
Air Suspension Dump Control (If Equipped)
If your vehicle is equipped with the Hendrickson HAS
Series single
-axle air suspension, you may have this
control. The air suspension dump control allows the
operator to lower the deck height approximately
4.5 inches (11.5 cm) from the normal frame height.
The switch to deflate and
inflate the air suspension is
located on the upper left
side of the instrument panel
above the driver's side vent.
The light in the switch will be illuminated whenever the
switch is in the ªdumpedº position.
Automatic Transmission Operation
We build vehicles with four, five and six-speed
automatic transmissions. This part of the manual covers
the basics of these. With some of the transmissions, you
will find another manual in your vehicle that goes into
more detail. On the ceiling, in front of and above the
driver, or in some other place near the driver, you will
see a label that describes important operating facts about
the automatic transmission in your vehicle. Make sure
you follow the instructions on this label.
You may have a PARK (P) position for your shift lever.
This position locks your rear wheels. It is the best
position to use when you start your engine because your
vehicle can't move easily.
All vehicles equipped with automatic transmissions
can be started in PARK (P), if equipped, or in
NEUTRAL (N). When you shift out of NEUTRAL (N),
you may have to hold in a push button on the shift lever
or lift up on a release handle as you shift. See the
Allison Automatic Transmission Operator's Manual in
your vehicle for more information about this.
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6-71
Name Circuits Protected
CHAS Exhaust Brake, Air Suspension
Dump Valve, Air Dryer, HYD
ABS ECHU
PARK LP Auxiliary Wiring, Air Conditioner
Controls, Parking Lamps, Turn
Signals, Taillamps, Stoplamps,
Marker Lamps, Trailer Running
Lamps, Lighted Mirrors, Radio
Receiver, Mirror Clearance Lamps
HORN Horn/Diagnostic Connector
PRK BRK Parking Brake Module
FUEL Heated Fuel Filter (Diesel
Engines) or Fuel Pump
(Gasoline Engines)
AXLE Heated Mirrors, Radiator Shutters,
Tw o
-Speed Axle Motor,
Tw o
-Speed Axle Switch
MRKR LP Roof Marker Lamps,
Trailer Marker Lamps,
Marker Lamp RelayName Circuits Protected
CIG/AUX Cigarette Lighter,
Auxiliary Power Jacks
AUX Auxiliary Wiring Relay
IGN RLY/VIN Vehicle Interface Module
(Diesel Engines) or Generator,
Coil, Injectors (Gasoline Engines)
WDO Power Windows
CRNK Starter Relay
IGN SW Instrument Panel Cluster Telltales
AUX Auxiliary Wiring
RDO Radio, Auxiliary Wiring
DR LK Power Door Locks
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7-6 12,000 Miles (20 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Chassis lubrication service (or every 6 months,
whichever occurs first). (12)

Lubricate door hinge pins and rollers with engine oil.

Wheels and tires service. (15)

Hydraulic brake service (or every 6 months,
whichever occurs first). (7)

Hydraulic parking brake service (or every 6 months,
whichever occurs first). (8)

Engine drive belts service (or every 12 months,
whichever occurs first). (18)

Clutch pedal free travel service. (10)

Throttle linkage service. (19)

Thermostatically controlled engine cooling
fan service. (4)(20)

Shields and underhood insulation service. (4)(5)(21)

Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours,
whichever occurs first).
15,000 Miles (25 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Steering system service. (13)

Front and rear suspension service. (14)

Spring
-to-axle U-bolts and shackle bolts service. (16)

Exhaust system service (or every 6 months,
whichever occurs first). (3)(4)(17)

Air brake service (or every 6 months, whichever
occurs first). (39)
18,000 Miles (30 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Chassis lubrication service (or every 6 months,
whichever occurs first). (12)

Inspect door hinge pins and bushings and replace as
necessary. Lubricate door hinge pins and rollers with
engine oil.
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7-8 24,000 Miles (40 000 km) (Continued)

Evaporative Control System service (if equipped) (or
every 24 months, whichever occurs first). (3)(26)

Rear axle air shift motor service. (11)
Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours,
whichever occurs first).
Air brake chamber service (or every 2 months,
whichever occurs first). (41)
Trailer brake hand control valve service (or every
3 months, or 900 hours, whichever occurs first). (42)
27,000 Miles (45 000 km)
Engine oil and filter service. (3)(9)
Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)
30,000 Miles (50 000 km)
Engine oil and filter service. (3)(9)
Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)
Chassis lubrication service (or every 6 months,
whichever occurs first). (12)
Replace fuel filter(s) (or every 12 months, whichever
occurs first). (3)Air cleaner filter replacement service (or every
24 months, whichever occurs first). (3)(4)(27)
Steering system service. (13)
Front and rear suspension service. (14)
Spring
-to-axle U-bolts and shackle bolts service. (16)
Exhaust system service (or every 6 months,
whichever occurs first). (3)(4)(17)
Air brake service (or every 6 months, whichever
occurs first). (39)
Lubricate door hinge pins and rollers with engine oil.
Wheels and tires service. (15)
Hydraulic brake service (or every 6 months,
whichever occurs first). (7)
Hydraulic parking brake service (or every 6 months,
whichever occurs first). (8)
Clutch pedal free travel service. (10)
Air brake automatic slack adjuster service (or every
500 hours, whichever occurs first). (40)
33,000 Miles (55 000 km)
Engine oil and filter service. (3)(9)
Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)
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7-10 45,000 Miles (75 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Steering system service. (13)

Front and rear suspension service. (14)

Spring
-to-axle U-bolts and shackle bolts service. (16)

Exhaust system service (or every 6 months,
whichever occurs first). (3)(4)(17)

Air brake service (or every 6 months, whichever
occurs first). (39)
48,000 Miles (80 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Chassis lubrication service (or every 6 months,
whichever occurs first). (12)

Lubricate door hinge pins and rollers with engine oil.

Wheel bearing (grease type) service (or every
24 months, whichever occurs first, and whenever
hubs are removed). (23)

Wheels and tires service. (15)

Hydraulic brake service (or every 6 months,
whichever occurs first). (7)
Hydraulic parking brake service (or every 6 months,
whichever occurs first). (8)

Engine drive belts service (or every 12 months,
whichever occurs first). (18)

Clutch pedal free travel service. (10)

Throttle linkage service. (19)

Thermostatically controlled engine cooling
fan service. (4)(20)

Shields and underhood insulation service. (4)(5)(21)

Air intake system service (or every 24 months,
whichever occurs first). (4)(5)(24)

Thermostatically controlled air cleaner service (or
every 24 months, whichever occurs first).
(3)(4)(25)

Evaporative Control System service (if equipped) (or
every 24 months, whichever occurs first). (3)(26)

Rear axle air shift motor service. (11)
Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours,
whichever occurs first).
Air brake chamber service (or every 2 months,
whichever occurs first). (41)
Trailer brake hand control valve service (or every
3 months, or 900 hours, whichever occurs first). (42)
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7-11 51,000 Miles (85 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)
54,000 Miles (90 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Chassis lubrication service (or every 6 months,
whichever occurs first). (12)

Inspect door hinge pins and bushings and replace if
necessary. Lubricate door hinge pins and rollers with
engine oil.

Replace air conditioning filter dryer (or every
18 months, whichever occurs first, and whenever
refrigerant charge is lost for any reason).

Wheels and tires service. (15)

Hydraulic brake service (or every 6 months,
whichever occurs first). (7)

Hydraulic brake caliper service (or every 6 months,
whichever occurs first). (22)

Hydraulic parking brake service (or every 6 months,
whichever occurs first). (8)

Clutch pedal free travel service. (10)
Spark plug service. (3)(28)

Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first);
lubricate linkage.
57,000 Miles (95 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)
60,000 Miles (100 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Chassis lubrication service (or every 6 months,
whichever occurs first). (12)

Replace fuel filter(s) (or every 12 months, whichever
occurs first). (3)

Air cleaner filter replacement service (or every
24 months, whichever occurs first). (3)(4)(27)

Steering system service. (13)

Front and rear suspension service. (14)

Spring
-to-axle U-bolts and shackle bolts service. (16)
(Continued)
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7-14 72,000 Miles (120 000 km) (Continued)

Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first);
lubricate linkage.

Air brake chamber service (or every 2 months,
whichever occurs first). (41)

Trailer brake hand control valve service (or every
3 months, or 900 hours, whichever occurs first). (42)
75,000 Miles (125 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Steering system service. (13)

Front and rear suspension service. (14)

Spring
-to-axle U-bolts and shackle bolts service. (16)

Exhaust system service (or every 6 months,
whichever occurs first). (3)(4)(17)

Air brake service (or every 6 months, whichever
occurs first). (39)
78,000 Miles (130 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)
Chassis lubrication service (or every 6 months,
whichever occurs first). (12)

Lubricate door hinge pins and rollers with engine oil.

Wheels and tires service. (15)

Hydraulic brake service (or every 6 months,
whichever occurs first). (7)

Hydraulic parking brake service (or every 6 months,
whichever occurs first). (8)

Clutch pedal free travel service. (10)
81,000 Miles (135 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Wheel bearings service
-- Eaton Axle (oil-filled) (or
every 24 months, whichever occurs first). (1)(23)
84,000 Miles (140 000 km)

Engine oil and filter service. (3)(9)

Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)

Chassis lubrication service (or every 6 months,
whichever occurs first). (12)

Lubricate door hinge pins and rollers with engine oil.

Wheels and tires service. (15)
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