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89 Chevy Alternator or belt??

Discussion in 'Truck & Equipment Repair' started by dichdoc, Jan 10, 2011.

  1. dichdoc

    dichdoc Junior Member
    Messages: 27

    I have an 89 Chevy 3/4 ton 350 with serpentine belt and dual batteries. Lately when I lift the plow the volt gauge drops to around 9 and everything dims and slows (It always dimmed but volts seem lower than I had noticed before) it used to rebound as soon as you shut the load off but now it seems to hang down around 9-10 volts. Today I popped it in park and revved the motor there was what sounded like belt noise and then the volts came back up. Thoughts?? The batteries were new last year and I have checked my grounds. TB
  2. kashman

    kashman PlowSite.com Addict
    Messages: 1,070

    look at your pulley
  3. dichdoc

    dichdoc Junior Member
    Messages: 27

    The alternator pulley? What should I look for? loose bolt securing it to shaft??
  4. theplowmeister

    theplowmeister 2000 Club Member
    from MA
    Messages: 2,617

    ether your batteries is not fully charged (slipping belt) or you have a bad batteries

    plow draws ~ 150 to 250 amps plus wipers headlights radio heater fan
    Altimeter 90 to 160 amps
    so the difference comes out of the batteries

    bad batteries, connection can cause voltage to drop, batteries not fully charged will have a drop in voltage.
  5. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    ya check for a glazed over belt . might be slipin. might also wana check to see if the belt self tensioner is getting stuck or weak and not holding the belt tight.

    and good upgrade is a 2-4ga wire from the alt back power post directly to the battery hot post. the weak little factory wire looses amps on big draws from stuff like plow motors.

    and if you realy wana help the system try one of these guys alts. http://shop.ebay.com/alterstart/m.html?_nkw=&_armrs=1&_from=&_ipg=25

    i got there 200 amp and it has let my truck run like a new one for electric . just a idea.

    i have a federal signal all light old street hawk bar 60-70 amps alone by its self all lit up. then heater on high / wipers goin / truck lights / plow lights / truck volts to run motor it was killin the 100 amp stocker. i got there 200 amp upgrade alt cs130 stock now cs144 from them direct fit and its 125 amp at 800 rpm and 210 amp at full output.

    my truck runs great. nothing dims. and my battery dosnt boil from to much power also.
  6. maverjohn

    maverjohn Senior Member
    Messages: 902

    I run the same truck you do and I have the same drop as you do, but it always return to 13.5 volts after the load is off. I'd try the belt first, It's the cheapest.
    Sweetk30 has some good points if you have other electrical problems.
  7. dichdoc

    dichdoc Junior Member
    Messages: 27

    So do you just add the 2 ga wire and leave the stock hooked up as well? The factory looks like it goes back into the wiring harness on the passenger side. I'll pick up a belt tomorrow and try it.
  8. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    you can just add it. since the voltage is regulated inside the alt.

    actualy if you did a bigger alt and diddnt upgrade the wire it would burn up real quick.

    the stock wire is fine for most everything. but the bigger wire option is a vary comon over looked thing.
  9. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    ya i had basicly to much amp's required and didnt have the amp's the system needed. so i upgraded real quick. and it solved all my problems. payup
  10. dichdoc

    dichdoc Junior Member
    Messages: 27

    Replaced belt and added a 2 ga wire direct from Alternator to + battery terminal. Seems to have helped. Gauge rebounds quicker will knwo more with some snow. TB
  11. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    glad to hear you seen some improvment already . wesport
  12. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    How old is the belt tension-er? It may be getting tired. I have seen plastic pulley's wear out too on them. Clean ALL your grounds, ALL black wires connected to the engine and frame. Protect with Dielectric grease! You can get bigger output alternators on the Internet. An automotive rebuild shop in town can rebuild your stock one for about a $1.50 an amp. So it will fit in the same spot.
  13. sweetk30

    sweetk30 PlowSite.com Addict
    Messages: 1,588

    the upgrade unit i got bolted right in place and same belt.

    plus my local guy never could give me a stright answer or time frame.
  14. MickiRig1

    MickiRig1 PlowSite Veteran
    Messages: 3,617

    Some engines have space constants with bigger size upgrade alternators.So you have to upgrade the one you have.Keep in mind too, that an alternator only puts out about 1/3 of it's rating at idle.Might even think about an add on volt gage. You should be running 13.5 --> 14.5 volts when running. If it's dropping your loosing ground somehow.
    Last edited: Jan 12, 2011