Declucthable fan doesn't de-clutch...it sticks 'on'
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Thread: Declucthable fan doesn't de-clutch...it sticks 'on'

  1. #1
    Fellow Frogger!
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    Default Declucthable fan doesn't de-clutch...it sticks 'on'

    The de clutchable (504) radiator fan on the younger of my 404s sticks in the locked position even after the power is switched off.
    Is this likely to be a problem of an electrical nature or something to do with physics...like sticking on the water pump shaft? It can usually be persuaded to back off after some manual manipulation with the motor switched off.
    The air gap is set to spec.

    All informed advice always appreciated

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    Cheers

    John

  2. #2
    1000+ Posts robmac's Avatar
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    Two suggestions, but based on conjecture rather than experience.

    1) Something mechanical. Ie springs with lost tension or mechanical jam.

    2) Magnetization of the magnet armature.

    In case two you hook the clutch coil up reverse polarity for a couple minutes to demagnetise.

    The first case is inspect and rectify.

  3. #3
    Fellow Frogger! stew's Avatar
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    What happens is the clutch faces are worn and slipping under magnetism. There are areas where it micro welds itself together hence the sticking together. You need to remove the hub and machine the faces back square to each other. We used to machine around 0.004" more off on the inner ring face on the pulley which helped the old springs in the front hub de clutch. Was it 0.7mm clearance or so?? if you have a look you will see some metal filings developing in the gap!
    robmac and Beano like this.

  4. #4
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    Thanks Rob and Stew,

    I'll get to and remove the thing and have a good close look at it next week.

    John

  5. #5
    1000+ Posts Wildebeest's Avatar
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    John,
    Despite good advice given my first thoughts were to clean the gap between the halves with something like spray degreaser or brakeclean. Then open the specified gap by a thou or three.

    PS. This is the lazy mechanic coming out in me!

  6. #6
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    Quote Originally Posted by Wildebeest View Post
    John,
    Despite good advice given my first thoughts were to clean the gap between the halves with something like spray degreaser or brakeclean. Then open the specified gap by a thou or three.

    PS. This is the lazy mechanic coming out in me!
    Wildebeest,
    I did something like a proper job today...pulled out the radiator, took off the pump and pulled the pulley off the pump.

    It all came apart nicely and when compared to a couple of spare water pump clutch mechanisms the non compliant unit definitely had weaker springs than the one now installed. I just gauged by 'feel' the pressure required to depress the fully backed off clutch onto the pulley.

    The clutch now installed looks like quite a youthful example with only factory black paint,shiny bolts, clean nylon bits and a yellow dot for some reason or other. It obediently clicks on and off and locks the fan as one would expect.

    This has been a learning process for me. You've got to love this a/frogs fraternity for the expert advice and input

    Thank you all

    John
    Wildebeest likes this.

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