GMC T-Series 1999 Owner's Manual page 273

Scheduled Maintenance (Except DURAMAX
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Check air brake relay valve operation and check for
leaks (or every month, or every 300 hours,
whichever occurs first).
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Clean air brake application valve (or every 3 months,
or every 300 hours, whichever occurs first);
lubricate linkage.
39,000 Miles (65 000 km)
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Engine oil and filter service. (3)(9)
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Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)
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Clean air conditioner filter (or every month,
whichever occurs first). See "Air Conditioner Filter"
in the Index.
42,000 Miles (70 000 km)
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Engine oil and filter service. (3)(9)
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Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)
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Chassis lubrication service (or every 6 months,
whichever occurs first). (12)
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Clean air conditioner filter (or every month,
whichever occurs first). See "Air Conditioner Filter"
in the Index.
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DIESEL)
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Lubricate door hinge pins and rollers with engine oil.
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Wheels and tires service. (15)
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Hydraulic brake service (or every 6 months,
whichever occurs first). (7)
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Hydraulic parking brake service (or every 6 months,
whichever occurs first). (8)
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Clutch pedal free travel service. (10)
45,000 Miles (75 000 km)
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Engine oil and filter service. (3)(9)
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Check fluid levels (or every 3 months, whichever
occurs first). (1)(2)(6)
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Clean air conditioner filter (or every month,
whichever occurs first). See "Air Conditioner Filter"
in the Index.
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Steering system service. (13)
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Front and rear suspension service. (14)
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- - -
Spring to axle U bolts and shackle bolts
service. (16)
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Exhaust system service (or every 6 months,
whichever occurs first). (3)(4)(17)
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