spin front wheel/hub while on stands, should opposing wheel turn the opposite direction??

Discussion in 'Gen 3 Prius Technical Discussion' started by viciousthinker, Apr 7, 2021.

  1. viciousthinker

    viciousthinker Junior Member

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    ok all, if you can decipher that title it kinda says it all, but to elaborate... i noticed a long time ago that when my 2012 Prius is elevated on jack stands (no e-brake set) if i try to spin the hub it spins freely, AND the opposing front wheel starts spinning too... the opposite direction. while it made little sense to me i assumed it was normal... is it? i’ve also noticed even aside from the (weird?) rotation there is a disturbing amount of play felt when i go back and forth fast... almost a slack feeling.

    within the last hour i was harvesting some brake bits off my forlorn 2010 “parts car”, which i lost to a headgasket failure years back... just out of curiosity i tried to rotate the drivers side front hub... and it moved all of a centimeter before meeti nd heavy resistance, i didn’t try to force it... but i noticed that the opposing hub didn’t move one iota, not a millimeter.

    which behavior is normal???:eek:
     
    #1 viciousthinker, Apr 7, 2021
  2. ChapmanF

    ChapmanF Senior Member

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    There is a differential mechanism that connects the two drive axles to the output of the transaxle. To allow the car to turn corners, it has to allow the two wheels to rotate at different speeds. It enforces the relationship that (final drive rpm) = (left wheel rpm + right wheel rpm) ÷ 2.

    If the car is raised, and it's in Park, the parking mechanism will prevent the final drive from turning; its rpm is held at zero. That forces the differential to make the left and right wheel rpm add up to zero; in other words, to be equal and opposite.

    In every gearbox there will be play; you are feeling the lash between the gear teeth in the differential, between the gear teeth in the final drive, and between the pawl of the parking mechanism and the notches it drops into. That's all normal.

    The heavy resistance in the parts car is what's not normal. The first thing I would suspect would be a dragging brake on the 'other' wheel, assuming you hadn't removed the brake on that side yet.
     
    #2 ChapmanF, Apr 7, 2021
    CR94 likes this.
  3. Team_Geek

    Team_Geek Member

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    This video is from Chevrolet back in 1937. It is a really cool video to visualize how a differential works.



    There is some back story and funny business to start the show off. Details start around 3:30. It’s a really neat old video and I’d recommend just watching the whole thing through.
     
    #3 Team_Geek, Apr 7, 2021
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