Alternator Pulley
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HT4100 4.1, 4.5, 4.9 Discussion, Alternator Pulley in Cadillac Engine Technical Discussion; 85 sedan deville... i've had the car for about 3 years...no major problems (replaced faulty ECM; caused parasitic drain to ...
  1. #1
    pfeil1sp is offline Cadillac Owners Member
    Automobile(s): 1985 Cadillac Sedan DeVille
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    Alternator Pulley

    85 sedan deville...

    i've had the car for about 3 years...no major problems (replaced faulty ECM; caused parasitic drain to battery, belt issue...i'm getting to that)...one issue i just can't seem to resolve...

    the alternator pulley on this car is CLEARLY not the right one. 6 grooves...so we're good there...but the dimensions - specifically, the WIDTH, are off. this causes a misalignment with the rest of the pulleys, forcing the belt to "bend" to the right about 4 or 5 mm. this in turn chops apart about half the belt, leaving me with nasty looking, albeit functional, 4 grooved belt.

    my question is simply this: does anyone (possibly an 85 deville owner) have the correct dimensions for the alternator pulley? if it helps, the car has a 108 amp alternator. i also understand that there exists two different pulleys (black and gold) which correspond to different belt lengths. as i know i have the wrong pulley on there now, i'll take any dimensions available, black or gold.

    dimensions of my absolutely wrong pulley:

    6 groove
    approx. diameter = 55mm (2.165 in)
    approx. width = 27mm (1.06 in)
    approx I.D. = unknown...but this fits perfect on the alternator, so it must be comparable to the correct I.D.

    any help would be great!

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  3. #2
    carnut is offline Cadillac Owners Master
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    Re: Alternator Pulley

    Years ago when I had this issue, I went to an auto parts store and asked to look at the old alternator cores they were returning. Found the correct pulley and had them swap it over. Gave the counter man a $5.00 tip! Obviously you carry in your alternator.

  4. #3
    Slacker is offline Cadillac Owners Fanatic
    Automobile(s): 1987 Cadillac Fleetwood Brougham
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    Re: Alternator Pulley

    Just replaced my alternator on my '82 Deville and I have the same exact problem!

    I revved the car high to test to make sure everything wasn't going to blow itself up.. and the alternator belt came off and was eaten by the fan. (I turned the car off but I guess the difference of a second makes a big deal when you're in a blender. )

    When I got out, I noticed that the alternator seemed recessed a little bit compared to the fan pulley. When I had my old core at the parts store they looked the same, but I guess it's a small difference that's only noticeable by standing and looking directly at the two pulleys.

    Is there a way to make the pulley stick out maybe 1/2 an inch further?

  5. #4
    carnut is offline Cadillac Owners Master
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    Re: Alternator Pulley

    Your car is a rear wheel drive. The original poster's car is front wheel drive. You have separate belts, he has one. On my Eldo's alternator, there is a tubing spacer at the rear mounting lug of the alternator itself. Is yours missing? Without that spacer, the alternator would be loose between the 2 bracket mounting holes, effectively moving the alt. about a 1/16 inch back. 1/2 inch misalignment is very severe, something else is either mounted wrong or spacers are missing? Be aware that if the smog pump belt is loose on your car, the alternator belt will slip on the water pump pulley. That leads to weak batteries and belt squeal with A/C on.

  6. #5
    Slacker is offline Cadillac Owners Fanatic
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    Re: Alternator Pulley

    Thanks for the help.

    Sorry, my mind slipped and I thought 85's were still rear wheel for some reason.

    The tube spacer is there... I used some washers to hold it forward more. And yes, it was way less than 1/2 an inch after inspecting again. (Chalk that up to bad on the fly measurements in my head. )

    I actually had that problem with the smog pump when I bought the car. The original owner must have driven it like that because they bent the pulley in the process some how. I replaced the smog pump and tightened it up (What a pain!) and now that's running well.

  7. #6
    carnut is offline Cadillac Owners Master
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    Re: Alternator Pulley

    Pheilsp, both the gold and black pulleys are the same width, just different diameters. So, theres something else misaligned. some alternators have a spacer ring under that pulley to move it forward on the shaft. Could that spacer be too narrow?

  8. #7
    ehall's Avatar
    ehall is offline Cadillac Owners Connoisseur
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    Re: Alternator Pulley

    I've gone through multiple alternators over the years, and one thing I've noticed is that some of the pulley are visibly pressed in too far. What I've done in those cases is use some good washers as spacers on the bolts. Your alternator should have two mounting tabs on the front and a third on the rear. Depending on where you put the washers, you can move it around a few mm at a time.

  9. #8
    pfeil1sp is offline Cadillac Owners Member
    Automobile(s): 1985 Cadillac Sedan DeVille
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    Re: Alternator Pulley

    Thanks for your help everyone. I've been informed that there should have been a spacer underneath the pulley, and that this likely was lost when a previous owner replaced the alternator (guy at autozone knew my problem before I explained it to him...I asked to see some alternators with pulleys...he asked if I had an alignment problem on the belt). This is what I originally thought the problem was, but I wanted to make certain, as I would rather have the correct pulley than a spacer on the wrong one. Turns out I do have the correct pulley (and it's gold btw), and thanks to a $0.34 purchase at the hardware store, an adequate spacer. The new belt is on, working just fine.

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