Use of 4HI or 4LO and 4HI Lock or 4LO Lock on Full-time 4WD is intended for use on a low traction surface such as snow, ice, mud or sand. On a low traction surface, the differences in front and rear axle speeds will not have as much effect on binding because of the lower traction levels between the surface and the contact patch of the tires. On a high traction surface, the higher traction levels will create more binding and noise in the driveline.
Driveline noises in 4WD or AWD vehicles caused by loading may be mistaken for transfer case or front axle noise because they can sound very similar. Four-wheel drive noises caused by loading may exhibit the following conditions:
• The noise will be greatest on a clear, dry road and decrease on a low traction surface. Front axle or transfer case noise caused by bearings, ring and pinion, or planetary gearing will be similar on all surfaces.
• The noises or feel that can be expected will increase while making a tight turn.
• The noises may be changed from a deceleration to an acceleration condition (or acceleration to deceleration) by raising or lowering tire pressure at one end of the vehicle.
Tire rolling rates can be a major factor in operational characteristics. Consider the following important items:
• All tires are the same size and brand. Tires of different brands may have different circumferences (or radius) even if they are the same size.
• Tires are set to factory recommended pressures. A tire with low air pressure will roll at a different rate.
• All tires have approximately equal amounts of wear. Tires with different amounts of wear will roll at different rates.
• All tires are the same tread type. Don't mix on-off road, all-season or street tires on the same truck as they may have different circumferences and roll at different rates.
• One or more of the tires may show small, short scratches around the circumference of the tire tread. The tire "scuffing" on the road surface causes these scratches.
Source - GM Service Information
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