GM Full-Size Trucks 1970-1979 Repair Guide

Drive Belts

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INSPECTION



See Figures 1, 2, 3, 4 and 5

Inspect the belts for signs of glazing or cracking. A glazed belt will be perfectly smooth from slippage, while a good belt will have a slight texture of fabric visible. Cracks will usually start at the inner edge of the belt and run outward. All worn or damaged drive belts should be replaced immediately. It is best to replace all drive belts at one time, as a preventive maintenance measure, during this service operation.



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Fig. Fig. 1: There are typically 3 types of accessory drive belts found on vehicles today



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Fig. Fig. 2: An example of a healthy drive belt



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Fig. Fig. 3: Deep cracks in this belt will cause flex, building up heat that will eventually lead to belt failure



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Fig. Fig. 4: The cover of this belt is worn, exposing the critical reinforcing cords to excessive wear



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Fig. Fig. 5: Installing too wide a belt can result in serious belt wear and/or breakage

ADJUSTMENT



See Figure 6



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Fig. Fig. 6: A gauge is recommended, but you can check belt tension with thumb pressure

Belt tension should be checked with a gauge made for the purpose. If a tension gauge is not available, tension can be checked with moderate thumb pressure applied to the belt at its longest span midway between pulleys. If the belt has a free span of less than 12 in. (30cm), it should deflect approximately 1 / 8 - 1 / 4 . in. (3-6mm). If the span is longer than 12 in. (30cm), deflection can range between 1 / 8 - 3 / 8 in. (3-9mm).

REMOVAL & INSTALLATION



See Figures 7, 8, 9 and 10



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Fig. Fig. 7: To adjust belt tension or to replace belts, first loosen the component's mounting and adjusting bolts slightly



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Fig. Fig. 8: Push the component toward the engine and slip the belt off



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Fig. Fig. 9: Slip the new belt over the pulley



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Fig. Fig. 10: Pull outward on the components and tighten the mounting bolts to specification

  1. Loosen the driven accessory's pivot and mounting bolts.
  2.  
  3. Move the accessory toward the engine until enough slack is created to remove the belt from the pulley.
  4.  
  5. Place the new belt over the pulley and move the accessory away from the engine until the tension is correct. You can use a wooden hammer handle, or broomstick, as a lever, but do not use anything metallic, such as a prybar.
  6.  

It is better to have belts too loose than too tight, because overtight belts will lead to bearing failure, particularly in the water pump and alternator. However, loose belts place an extremely high impact load on the driven component due to the whipping action of the belt.

  1. Tighten the bolts and recheck the tension. If new belts have been installed, run the engine for a few minutes, then recheck and readjust as necessary.
  2.  

 
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