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I had to change serpentine belt on my road trip in "professional" service. They changed belt tensioner also. When we continued we realized that cruise control and most of A/C buttons don't work. So we drove back and they fixed it by tightening/connecting some tiny vacuum hose.

But now we are hearing much more noise from car (transmission) when on 1st and 2nd gear. So during uphill and starting its like tractor or some diesel engine. Not always. Usually in morning or when engine is cold. But in steep uphill kind of always.

And switching those first gears make really bad sound - like its teeth (if there are some) make friction. Again - few days later - it's not making any sound when manually switching 1st and 2nd gear. Just automatic switching makes louder (bad) noise than before.

I'm sure before service it was ok, because we drove 100km with partly-teared serpentine belt to the service without these sounds. I know there was slight sound when changing first two gear before, but nothing serious I would say - just normal switch.

Also I hear different sound from car than before - I hope it is the new belt and tensioner - it's like fast repeating ticking. I can recognize it when idling.

So is there something which could be disconnected or otherwise had some negative effect on transmission during belt change?

Car is:

  • Chevrolet Lumina APV (minivan) 1996, 3.4L V6.
  • Automatic transmission
  • 4 gears (1,2,D,OD).
  • Engine was replaced around 137,000km together with transmission.

Don't know when was the transmission oil changed last time so let's assume it was not. Car has now 209,000km.

Ad 1: At morning I tried manually switching to every gear and 1st made that “friction” sound.

Anyway “drastic” sound change occurred after belt change.

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So we visited A LOT of services and no one knew what was wrong. But every mechanic told that it should not be caused by serpentine belt.

In one special service which specialization was just transmissions - two guys took a look at it and said that it's not transmission related and sent us to other service where the guy checked it and said that it could be by bad GAS quality in Wyoming/Montana (plus they are adding ethanol - at least in Montana) and by old engine oil (plus different grade 10W-30 instead 5W-30). He was saying something about carbon deposits too. Also transmission fluid was old - but not burned.

So we changed oil, trans. fluid (with filter of course) and took Premium gas (still with ethanol) and it's much much better. During starting it's calm, during shifting it's calmer than before problems and I heard that grinding sound only twice during shifting from 1 to 2nd gear. And when it's warmed up it's like kitten.

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