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new drive belts when upgrading alternator?

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GMT800 99 Sierra 1500 5.3L V8, auto trans, a/c


I'm upgrading the factory alternator (~100 amps) to a professionally rebuilt alt (275 amps). I'm doing the "big 3" myself, have 4-gauge marine-grade wires, fuse box, and other stuff arriving soon. One last thing: the accessory drive belts. One is for a/c and the other is for everything else: power steering, water pump, alternator, etc. Since I'll be removing the belts, this is a good time to look at new ones.


The main accessory belt I have is slightly discolored, probably just dusty. I'm not sure how to check for wear but the the "tracks" look consistent: no cracking, chips, gouges. I haven't noticed any problems while driving or idling. One thing I did read is that a more powerful alternator puts more wear on the belt. I wonder if there are good aftermarket belts that are more durable without a huge price premium...


So, should the belts be replaced and if so what brand/type do you recommend? What prices I should expect to pay?

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How many years and miles does the current belt have on it?


I never had any luck with aftermarket belts, just buy the GM belt. You might want to replace your tensioner also depending on miles.

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The truck was bought used with 79,000 miles, not sure if/when the belt was replaced. So assuming this is the original belt, you think it will be fine up to what point? I drive conservatively and based on the vehicle's condition I doubt the engine was abused by previous owners.


I located a new pair of gatorbacks for $38 shipped. Models are:


4040377 - 4-rib, 37.75"

4060930 - 6-rib, 93.00"


Is this a worthwhile purchase? Has anyone had problems with these belts?

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Since you don't know the age of the belts, I would replace them. Can't comment on the gatorbacks.

Store the old belts somewhere in your truck and then if you lose a belt you are covered in an emergency.

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Thanks, one thing I found by searching for belts is that various part locators give different lengths.


92.32" - V8 w/ air conditioning and 105 amp alternator

93.00" - V8 w/ air conditioning and 130 amp alternator


Option codes for the some stock amps are:


K68 - 105 amp

KG8 - 130 amp

KG3 - 145 amp


So my belt length is 92.32" assuming the truck still has the stock alternator.


How do I determine what belt length the new alternator requires? It says bolt-on replacement, no other parts needed, but I don't see how it can work with two different belt lengths. It includes a pulley. I suppose if I line up the new pulley with the old one I should be able to tell if it needs a larger belt...

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More confusion...this time with a/c belt sizes.


O'Reilly's says 38.5"

Summit Racing says 37.75"


Not to be outdone, Car Stuff lists both 38.5" and 37.75" belts for my truck.


EDIT: Ha! it couldn't be easier. My belt part numbers are 4PK960 and 6PK2345. 960 mm = 37.8" and 2345 mm = 92.3".

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