New Alternator-Old mounting bracket doesn't fit?

Discussion in 'Troubleshooting & Diagnosis' started by wdstamper, Dec 29, 2017.

  1. FlaJunkie

    FlaJunkie Veteran Member Lifetime Gold Member

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    I bought a 12SI alternator from these guys. It works very well in the new harness and is internally regulated. It is beefier than the original alternator and provides better performance over a "one-wire" racing alternator for street use. It costs about $170. It outputs 140 amps. There is a higher output one available. You need to decide how many amps you need. Do you have electric fans or a high amp sound system? If not, the 140 amp model is fine.

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  2. wdstamper

    wdstamper Veteran Member

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    I looked up the Lester 7137 number and cross referenced to the replacement model which has the wrong bolt pattern for my car. I also found a Wilson 90-01-3109 allternator that should bolt right on assuming the picture is correct. Thanks for everyone’s help.

    Walt.
     
  3. McCune

    McCune Veteran Member

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    7137-3 15 SI . What year are you working on? That Wilson # crosses to a 7137-3. Delco #s are 1101044, 1101066, 1101088, 1101093, 1101442, 1105186, 1105342, 1984271.
     
    Last edited: Dec 30, 2017
  4. wdstamper

    wdstamper Veteran Member

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    McCune:
    My car is a 1981 z28. Is that the wrong one? Thanks.

    Walt
     
  5. McCune

    McCune Veteran Member

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    I believe your car was option with the higher amp 15 SI alternator. The original alternator you posted appears to be a original unit. it even had the plastic clip that is next to the battery stud. I would put that same 15SI back on your car and not try to hack a 12 SI in its place. Did you also notice that the adjustment bolt is a 10mm bolt and not a 8mm?
     
  6. wdstamper

    wdstamper Veteran Member

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    I did not. I went back to the auto parts store and retrieved my old alternator. I think at this point I’m going see if I can have a local shop rebuild the unit. Thx.

    Walt
     
  7. Dave Nelson

    Dave Nelson Veteran Member

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    That would be the best option.
     
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  8. Damon

    Damon Veteran Member

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    Yeah, that's a 15SI or 27SI alternator. Despite their higher designation number, they are basically the same operating principles as the common old 10SI series alternators. Physically larger case and higher output rated, but basically the same electrically-speaking and still with exposed cooling fan blades.

    The 12SI is a later design alternator (and a direct bolt-in for any 10SI alternator, but NOT for a 15SI or 27SI) with enclosed plastic cooling fan blades, much better low RPM performance and with amperage ratings of various models comparable to the old 15/27SI. This is still all v-belt vintage stuff I'm talking about here- roughly 1985-down.

    The 15/27SI is a bit of an oddball, but if you're going for that vintage look they work OK. If you're building a high RPM engine you should know that they tend to "explode" at high RPMs with some regularity.

    My Malibu came with a 10SI (63A) from the factory that I replaced with a later model 12SI (94A). Doesn't sound like much of an upgrade but it bolted right on and holds onto target voltage like a pit bull even at idle. The plastic cooling fan on the front doesn't look right for my vintage of Malibu but I don't care. It works far better than the stock unit in the real world.

    Last thought- the rear bracket retaining bolt on pretty much any GM alternator serves no real purpose. You can hack the arm off it and run it like it's just a spacer and you'll never have a problem. The attachment arm on yours is absolutely unique to the 15SI/27SI series of alternators and won't fit anything else, as you have learned.
     

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