| [GMCnet] new noise after alternator swap [message #304292] |
Tue, 26 July 2016 17:08  |
Ek_Lektro
Messages: 167
Registered: March 2011
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Senior Member |
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Might be a coincidence, but right after i did that alternator swap last week, whenever Los Angeles traffic allows me to get up to 50 MPH, there’s some new “noise” happening… hard to describe… sounds like some engine “hum". This noise only happens when accelerating. When i’m coasting down a hill and surpass 50MPH, there’s no noise.
First suspicion: During the alternator swap, i put in a new belt, slightly shorter 15565, because the 15570 was requiring the adjuster bracket to go to its full maximum. During the road-side swap, I could see that the pulleys were not 100% parallel to each other (but pretty darn close). Is it possible that a slight misalignment might cause some fairly serious noise at higher speeds? (i don’t hear ANY difference in engine compartment noise during slower speeds)
Or, my 2nd guess: Could a failing fan clutch maybe kick in only at these higher speeds / RPMs?
If the belt might be the culprit, then I’d have to do some pretty serious work with washers to get the pulleys to line up 100% parallel (or maybe easier by returning to the longer belt).
And if the fan clutch is a suspicion, of course its not too expensive to just swap it and see… (though this one is only a couple years old).
Figured i’d check with the more experienced GMC’ers before i dug further into it :)
Other background info, this is the ’78 w/403 engine, 370 final drive;
...and with a pesky tranny leak of unknown source, which means its hard to keep up with precise fluid levels.. but i think fluids were normal during my recent test drives. (I’ve been watching Ray’s progress on his tranny, Maybe i gotta try double o-rings when i do the filter and inspect things next week)
Lastly, I’m paranoid about engine compartment noise, so i didn’t push the coach past 55MPG to see if the noise might go away
OK, Thanks again for any advice!
Greg / Los Angeles
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