| [GMCnet] new noise after alternator swap [message #304292] |
Tue, 26 July 2016 17:08  |
Ek_Lektro
Messages: 167
Registered: March 2011
Karma: 2
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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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| Re: [GMCnet] new noise after alternator swap [message #304296 is a reply to message #304292] |
Tue, 26 July 2016 18:10  |
jhbridges
Messages: 8412
Registered: May 2011
Location: Braselton ga
Karma: -74
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Senior Member |
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I have learned to respect new noises - something is making them every time. Sometimes I identify it as something innocuous but sometimes it ends up being something that matters. Consider a run down the road with the hatch off.
--johnny
Foolish Carriage, 76 26' Eleganza(?) with beaucoup mods and add - ons.
Braselton, Ga.
I forgive them all, save those who hurt the dogs. They must answer to me in hell
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| Re: [GMCnet] new noise after alternator swap [message #304327 is a reply to message #304292] |
Wed, 27 July 2016 09:18 |
timthenomad
Messages: 63
Registered: June 2015
Location: Austin, TX
Karma: 5
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I once had an alternator noise that ended up being that the small alternator fan behind the pulley was making contact with the vacuum feed line for the heater controls. The line had enough slack in it that it had fallen out of sight on the underside of the alternator. At high RPMs it sounded like a bearing going bad, wasn't until I went to remove the alternator that I noticed the wear on the vacuum line.
Might be worth if to have a look and make sure it's not something as simple as that.
--tim
Tim Taylor
Austin TX
Philadelphia PA
76 Birchaven (SB)
76 Triumph TR6
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| Re: [GMCnet] new noise after alternator swap [message #304336 is a reply to message #304292] |
Wed, 27 July 2016 11:14 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Only when accelerating means when engine is producing power (torque more correctly). New shorter belt has alternator swung higher. It may be contacting aluminum body spar and conducting "hum" from powertrane. Could be tired engine mounts. Try brake torqing with hatch off and see if it is hitting.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] new noise after alternator swap [message #304374 is a reply to message #304292] |
Wed, 27 July 2016 16:46 |
Ek_Lektro
Messages: 167
Registered: March 2011
Karma: 2
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Senior Member |
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hey, Thanks for the great suggestions everybody. I’ve got my homework to do now:
> Is it more of a high pitched whine? If so that may be a normal alternator noise...
hey Nathan, i know what you mean, but this is more of a low-end humm…
> Only when accelerating means when engine is producing power (torque more correctly). New shorter belt has alternator swung higher. It may be
> contacting aluminum body spar and conducting "hum" from powertrane. Could be tired engine mounts. Try brake torqing with hatch off and see if it is hitting.
> —
this makes sense, John, and i’ll check it out. The new motor mounts are only a few years old on this coach, but things are still a bit loose up front with regards to cracked aluminum “struts”, on both sides… if that’s what you mean by "aluminum body spar"… Never was a problem before, but we might be on to something here.
> I once had an alternator noise that ended up being that the small alternator fan behind the pulley was making contact with the vacuum feed line for the heater controls. At high RPMs it sounded
> like a bearing going bad...
ok, i’m gonna check for that as well, thanks Tim
> Consider a run down the road with the hatch off.
Seems like that’s in my future, Johnny;
55MPH with the hatch off (with 370 final drive) is gonna be a loud loud drive!
Will report back as things progress…
Thanks all!
Greg / SolarSonic / Los Angeles
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