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Alternator Testing

Discussion in 'Intermediate CJ-5/6/7/8' started by bigjohn, Apr 3, 2020.

  1. Apr 3, 2020
    bigjohn

    bigjohn Active Member

    Kelso Wa
    Joined:
    Mar 18, 2010
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    1,054
    I noticed my charging system wasn't charging the other day on my 74. I contemplated switching to a delco 10si or 12si like I did to my other 5, but thought it best to just run stock Motorola since there wiring is relatively unhacked.

    So I put a new alternator and regulator on land it's still only charging at 12.6v. It goes up to maybe 12.9 with the thre rpms up, but turn the headlights and it drops to low 12. Add the heater fan and its like 11.6v at a little over idle. I changed the wire ends on the starter solenoid and alternator as they were corroded and frayed. This made little difference. I've measured voltage at the ignition side of the solenoid, the battery pole of the alternator and the battery.

    The amp gauge reads just positive with no lights, at zero with the lights on and revved up, and negative with headlights and heater on. The alternator light is functioning correctly, coming on with the motor off key on, and goes away when started. It flickers on briefly when you shut off the ignition as the motor slows to rest.

    Are there any other tests I can do without braving the flaps for alternator testing?
     
  2. Apr 3, 2020
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    cordele, Ga.
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    Make sure the voltage regulator has a good ground and the three wire coupler connections are clean. Be sure the belt is tight.
     
  3. Apr 3, 2020
    timgr

    timgr We stand on the shoulders of giants. 2022 Sponsor

    Medford Mass USA
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    The flowchart in the TSM covers a bunch of things like Walt mentions. Battery cables, tight belt, etc.

    The Motorola alternators were well known for bad diodes. The TSM covers this - they expected the mechanics to disassemble the alternator, unsolder the diodes, and test them with a volt-ohm meter. If you want to take the alternator apart and see what's up, the TSM will show you how. I've taken Delcos apart, but not Motorolas - I think it's pretty easy, since the brush assembly is removed before the case halves come apart.

    However, I think it's unlikely you will find replacement parts so you can repair your Motorola alternator today. The reman factories have the volume to get these obsolete parts, but it seems unlikely they would be available through retail channels today. Even if they were, you probably could not fix it for the cost of the reman. If you had an oscilloscope, I would expect the shape of the charging waveform to show the effect of bad diodes.

    Could be a regulator problem too. Again, the TSM has diagnostic tests for the electrical system. It's the last item on the flow chart.
     
    Last edited: Apr 4, 2020
  4. Apr 3, 2020
    bigjohn

    bigjohn Active Member

    Kelso Wa
    Joined:
    Mar 18, 2010
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    1,054
    Ok thanks guys. One more item, it still runs with the battery disconnected, just not at idle and a little more roughly. This tells me it's charging, just not where out should.

    I'm really regretting poor life choices... can I use the alternator bracket from a later 10si clad 304 and bolt a delco Remy on without having to cut and rebuild the existing bracket? I'm already $110 into this Motorola and already over it.
     
  5. Apr 4, 2020
    zila

    zila I throw poop

    Rock Springs,...
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    Oct 6, 2003
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    1,201
    I have a 304 and ditched the Crapola alt for a Delco. I believe mine is a CS 130, but can't remember. Anyhow Everything fit cept the rod thing going to the block. I measured both alts and shortened this piece the difference.. It had to be re-threaded but everything fit up correctly.
     
  6. Apr 4, 2020
    bigjohn

    bigjohn Active Member

    Kelso Wa
    Joined:
    Mar 18, 2010
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    1,054
    There solution was too embarrassing to not share.....

    Loose belt. :banghead::censored:

    The bright side, every connector to the alternator is new now....
     
    Lockman, Walt Couch and Fireball like this.
  7. Apr 5, 2020
    Keys5a

    Keys5a Sponsor

    Florida Keys
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    Glad you found the issue and have it charging again!
    -Donny
     
  8. Apr 5, 2020
    Walt Couch

    Walt Couch sidehill Cordele, Ga. 2024 Sponsor 2023 Sponsor 2022 Sponsor

    cordele, Ga.
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    There have been thousands of alternators sent to rebuilders as cores only to find nothing wrong. Loose belts are very common with alternators.
     
  9. Apr 5, 2020
    zila

    zila I throw poop

    Rock Springs,...
    Joined:
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    As are loose battery connections
     
    Walt Couch likes this.
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