GMC 2003 GMT560 T-Series Owner's Manual page 248

Trailer brake hand control valve service (or every
3 months, or every 900 hours, whichever occurs
first). (42)
Fuel tank, fuel cap and fuel lines service (or every
72 months, whichever occurs first). (3) (30) †
Thermostatically controlled engine cooling fan
service. (4) (20)
Shields and underhood insulation service. (4) (5) (21)
80,000 Miles (128 000 km)
Change engine oil and filter (or every 12 months,
whichever occurs first). (2) (3)
Air compressor dry element pleated paper air strainer
service (or every 2 months or every 800 hours,
whichever occurs first).
82,500 Miles (132 000 km)
Check fluid levels (or every 3 months, whichever
occurs first). (1) (6)
Chassis lubrication service (or every 6 months,
whichever occurs first). (12)
6-14
Wheels and tires service. (15)
Hydraulic brake service (or every 6 months,
whichever occurs first). (7) (46)
Parking brake service (or every 6 months, whichever
occurs first). (8)
Air brake service (or every 6 months, whichever
occurs first). (39)
Air brake automatic slack adjuster service (or every
500 hours, whichever occurs first). (40)
Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours, whichever
occurs first).
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 every 900 hours, whichever occurs
first). (42)
Wheel bearings service – Eaton Axle (oil-filled) (or
every 24 months, whichever occurs first). (23) (46)