What is the small round metal "ball" mounted to the front of the sub-assembly cross member?

Discussion in 'Gen 2 Prius Technical Discussion' started by TroyF, Nov 20, 2017.

  1. TroyF

    TroyF Junior Member

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    What is this, and is it important?
    When I removed the cross member sub-assembly from my 2005 Prius, this small metal "ball" thing fell to the ground. It was attached to a large washer on a small bolt at the front of the cross member bracket, and just behind and above the center engine mount. I am holding it in my hand in the picture near where I think it goes. It is almost all solid metal with a large hole in the center, and 3/8 inch of rubber pad at the bottom where I presume it attaches to the cross member bracket. I have everything painted black now, but it was quite rusty, and the rubber portion barely hanging on.
    So I am wondering if I should try to reattach it, and is it really important - or just leave it off? My best guess is that it helps dampen vibration somehow. The only way I see to reattach it would be to weld a bolt onto the cross member and bolt this down. But that would defeat its vibration dampening qualities (if it had any).

    Troy
     

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    #1 TroyF, Nov 20, 2017
    Last edited: Nov 20, 2017
  2. MickyMatter

    MickyMatter Active Member

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    I'm not sure. But after a Google Image search for the part number of the cross member, I found these pictures (2008 Toyota Prius Sub Frame - 51201-47030 - Used - A Grade.)
    It looks like a absorber for a special frequency. So for a proper function the correct mass and the right stiffness of the rubber is needed. Normally the rubber is vulcanised directly to the metal. Maybe a good adhesive will do, but I doubt that it will last forever.
    The cube in the near seems to be an absorber, too, but of course for another frequency.
    I think these absorbers are only for a better comfort and not for a longer lifetime of the cross member and the nuts and bolts (fatigue stress).
    If there appears a NVH problem in the late development process, an absorber or damper is often the right solution to reduce a "boom"/"eak"/rattle occurring in special situations.
    For lifetime issues such an absorber for a fix frequency is too risky. At the one hand often you can't reduce the problem of fatigue to one frequency, because the parts are stressed with different frequencies from ignitions and tooth wheels and so on, and reducing only one of them won't help a part living much longer (except it's the eigenfrequency, but this can be changed easy) and on the other hand Temperature and ageing changes the frequency of the absorber and reduces it's function. And a lost absorber can't work, too.
    Only my personally theory! So I, personally, would try some powerful adhesive and if it's getting lost, ¯\_(ツ)_/¯


    SM-G900F ?
     
    #2 MickyMatter, Nov 21, 2017
  3. Dxta

    Dxta Senior Member

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    That seems to me it came out from a failed engine mount.
    We of those have some stuff like grease embedded in them. If that stuff isn't in the engine mount you removed it again, replace the mount. You'd probably start hearing clunky noises now.

    Dxta
     
    #3 Dxta, Nov 21, 2017
  4. valde3

    valde3 Senior Member

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    Maybe it was hit with jack when lifting the car at some point. Or maybe it was hit with somethong on the road. If this was my car I would probably just leave it out. It’s there to reduce some vibration but probably you won’t feel any difference. And it’s very unlikely that the vibration would be strong enough to brake anything.

    No it’s not. See the link that MickyMatter posted it’s a mass damper.
     
    #4 valde3, Nov 21, 2017
    Dxta likes this.
  5. TroyF

    TroyF Junior Member

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    Yes, that picture shows the absorber in the place that I thought, and your description fits what I thought would be the function. I had to look up "eigenfrequency" as that is a new word for me. It doesn't appear that Toyota sells this part separately that I can find. I will put my cross member back together without the part at this point.

    Thanks.

    Troy
     
    #5 TroyF, Nov 21, 2017
  6. TroyF

    TroyF Junior Member

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    The absorber was so rusted that the rubber was separating from the metal it had been vulcanized to. I think it was just hanging onto the bolt protruding from the cross member, and when I tipped the cross member over while removing it, it just fell off. It is above where the jack would be, so the jack couldn't hit it.
     
    #6 TroyF, Nov 21, 2017
  7. valde3

    valde3 Senior Member

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    I was mostly thinking that if somebody didn’t know or accidentally jacked from wrong place. But I didn’t really look into it so maybe it’s actually not possible.

    But that won’t change my opinion about the part. If actual engine mount is ok I would just leave that part out.
     
    #7 valde3, Nov 21, 2017
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