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Alternator squealing under load at low idle

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Can Can, Dec 30, 2003.

  1. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    The cold hit hard here yesterday. Last night I was stopped at a red light and I could hear a squeal coming from the engine bay. The lights were on and the heater fan was on high.

    I got home and checked under the hood and realized that the sound was coming from the alternator. It only happens when the truck is idling and the alt is under a heavy load(lights and fan on).

    Is this a sign of a weak alternator? Or maybe a dying battery? I can replace both for under $200 so I may just do that(both the battery and alt are over 6 years old) and eliminate the need to troubleshoot in -30' weather, but I'm just curious what might be causing the alternator to squeal.
     
  2. slider

    slider 1/2 ton status

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    Loose or burned belt????????? Once its glazed-burnt it will never stop squeeling
     
  3. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    Weird thing is my girlfriends 97' fud taurus did the exact same thing with the heater on high,lights, windshield wipers... started humming at idle and the belt wasn't slipping because it's serpintine. Maybe your altenator(and hers) are about to give out. Do they make noises besides the belt anyone?
     
  4. emoo99

    emoo99 1/2 ton status

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    Thats kinda wierd i changed my alternator today kuz everytime i was at idle with all my accessories on mine would squeal really bad and it wouldn't stop unless i turned it all off and gave it some rpm's and it finally crawled back up to 14 volts.. All day today no squeal, got my alternator at shucks for about $115 and it's a 92 amp.. the biggest they carry for our trucks, plus it has a lifetime warranty, can't beat that.. buy some belt lube stuff and wait a day or 2.. see if the squeal goes away, just don't waste your money on an alternator if you don't need one, kinda sounds like you do if it's only at idle when your drawing more amps than it's puttin out..
     
  5. 83ZZ502_Jimmy

    83ZZ502_Jimmy 1/2 ton status

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    Sounds like the belt to me. But a new battery is certainly good insurance in -30 deg weather. /forums/images/graemlins/smile.gif

    John
     
  6. R72K5

    R72K5 Banned

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    would be either worn glazed pulley, or worn glazed belt, or both, or misaligned pullies

    i would go with new pulley if its not already new, pulley is about three bucks at a lcoal eletric motor shop and is easy to change, all you need is impact gun and socket and the pulley nut will come right loose /forums/images/graemlins/laugh.gif

    either that or its internal wear of alternator, probably bearings dried up and burning, does it make any growling noise ? or anything ?
    or only squealing ? try spinning alternator by hand with belt off and see how it spins, it should spin quietly and smoothly if is in good shape


    good luck /forums/images/graemlins/laugh.gif
     
  7. BamBamblazer

    BamBamblazer 1/2 ton status

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    I had the same thing on an 86 i used to have. Replaced the belt, no difference. Finally figured out that the bushings or bearings(i dunno what it has) on the alt. were worn and that was causing the squeel. Just a thought as it happened to me. /forums/images/graemlins/confused.gif
     
  8. slider

    slider 1/2 ton status

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    UMMMM serpentine belts can slip when the tensioner wears out. Had a customer's truck that kept over heating found the tensioner would move when the load changed and then the belt would slip, not much but enough to make the truck run warm while driving, It was fine at idle. I got lucky and remembered one of our instructors at school had the same problem.
     
  9. dyeager535

    dyeager535 1 ton status Premium Member

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    I'd probably pull the belt and spin the alternator by hand. If its the bearing(s) or other internal pieces, that noise should be evident when you turn it by hand, or you should feel the "roughness" in how it turns.

    There is probably some endplay measurement for the alternators, but if this one is strong enough for you, a rebuild kit for one costs $25 here, and is EXTREMELY simple to do. I understand not wanting to work in the cold, but you'd have to pull it anyways if its the problem. I believe the kits don't come with the rear bearing, and although it sees no load really, I replace it too. (I think my last rebuild took 30 minutes including time to pull and replace it)

    If you wanted to attempt the rebuild yourself, buy the kit, head home, pull the belt, and check if the alternator is the cause or not. If it isn't, return the kit and fix the problem. If it is the problem, you've already got the belt off anyway, now you can take the alt. inside and rebuild it.

    I really don't know of any test for mechanical, not electrical, problems with the alternator. There may be one or two in the manual, but I don't have mine handy.
     
  10. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Thanks for all the input, brothers. I'm gonna check out the belt/pulley tonight and go from there. I'll keep you updated when I find something out.
     
  11. K05Aggie

    K05Aggie 1/2 ton status

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    My alternator started squealing three days ago. The next day I could smell it burning up while driving with the windows down (it's still in the 70's here) and the case was unusually hot. So I bought a new one and pulled the old one off. Immediately after I took it off I couldn't get it to spin 1/4 turn, but now that it is cool it spins freely and smoothly.
    I'd guess in your case the belt is slipping.
     
  12. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    I should have updated this a couple of days ago. I ended up getting rid of the squealing by tightening the belt and gently sanding the belt and pulley. I was able to pull the alt about a 1/2" tighter on the pivot!!!!

    FWIW, there was no play in the pulley and no audible signs of internal wear. The pulley spun freely in both directions with no grinding etc...

    I wonder how the belt got so loose all of a sudden? /forums/images/graemlins/confused.gif
     

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