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Thread: Issue with Tightening Rear Axle Nuts

  1. #1
    Join Date
    Apr 2002
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    Overland Park, KS
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    4,054

    Issue with Tightening Rear Axle Nuts

    So perhaps I am just loosing my mind here or having a senior moment, but this seemingly mundane task of torquing down the rear axles nuts has my completely confused. I've worked on these cars for years and have had half shafts in and out of these cars dozens of times, but it has been a while. This latest work involved changing the axle seals and replacing both half-shafts with re-manufactured Ford parts and those silly aftermarket nuts (think Dorman style) on my 1997 with an automatic transmission. There is probably a simple explanation for what I am finding and you will probably all laugh at me, but I can't get it through my non-engineering mind....

    When I go to actually torque down the axle nuts, the half shafts just turn, as if the car isn't in park. I go to turn the nut on the right side, and the hub and half shaft both turn, and so does the one on the other side. I try the left one, and same thing. I rolled under there to ensure I got both shafts fulling "clipped" into the differential, and they are nice and tight and I heard that nice "click" sound when inserting them. When I try to turn the half shafts by hand up close to the differential, they engage the pinion gear and won't turn as the car is in park and the driveshaft will not allow it. Just as you would expect.

    So... how in the world can I spin the whole assembly when trying to torque down the axle nuts, as if the pinion gear wasn't there or the car was in neutral, yet when I turn the half shaft by hand it won't move. I thought perhaps something was slipping in one of the joints of the half shaft, but if that was the case, then the movement shouldn't be transferred from one end through the differential to the other end. It all seems to be connected and working in that regard. The splines on slide well into the hub, nice and tight but without issue, and the hub turns when the half-shaft turns, just as you would expect it to.

    The car was being driven without any noticeable issues to the rear end other than leaking seals and a half shaft with a torn boot. The factory trak-loc worked well, and inspection when I pulled the cover to change the fluid didn't reveal anything out of the ordinary. No pieces in the case, clean parts, no sheen to the oil from metal shavings, no broken clutch teeth, etc. I can torque the axle nuts with the wheels back on the car and on the ground, but shouldn't I be able to do it without as long as the car is in park? What am I missing here?

    Thomas

  2. #2
    Join Date
    Jun 2013
    Posts
    128
    That's normal, just put a long bar through the wheel studs on the other side have it pressing against the floor. Thiten the axel, then switch sides.

  3. #3
    Join Date
    Feb 2003
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    Tinton Falls, NJ
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    1,502
    With an open differential, when you turn one wheel, the other will turn in the opposite direction, even if the car is in park. Snug up the nut, then install the wheel with the center cap off, and drop the car back down on the ground to do the final torque with the wheels on the ground and the car in park.

  4. #4
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    Apr 2002
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    Overland Park, KS
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    Thanks guys. It has been years since I've done this, so I just wasn't sure. The differential does have trac-lok (verified when I had the cover off), but I guess that works the same. I just couldn't get it right in my mind as to how that is possible, probably because I don't have a good enough understanding of how everything works in the rear end.

    So looking at a picture of the carrier itself, I think I might finally get it. I'm a little slow sometimes. It would appear that when you turn the half shaft, it is turning the gears in the carrier, but it is just those gears that are turning. You are not rotating the whole carrier unit, to which the ring gear is attached. Since you are not turning the ring gear, it is not attempting to turn the pinion gear. When you are driving the car, the input is coming from the opposite end. It starts at the pinion gear, transfers to the ring gear, which turns the carrier and the smaller gears inside of the carrier and transfers power out to through the half shafts to the hubs and wheels that are bolted to them. Just needed a little engineering lesson....
    Last edited by Thomas A; 10-20-2016 at 11:31 AM.

  5. #5
    Join Date
    Jul 2003
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    Ottawa, Ohio
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    5,397
    I usually mount the tire back on and lower it down to use the friction of the pavement to tighten the axle nuts.
    SCCoA Member#: 2515
    1990 SC AOD 2.1L Kenne Bell
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  6. #6
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    Dec 2007
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    Salem, OR
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    6,340
    Quote Originally Posted by Thomas A View Post

    So looking at a picture of the carrier itself, I think I might finally get it. I'm a little slow sometimes. It would appear that when you turn the half shaft, it is turning the gears in the carrier, but it is just those gears that are turning.
    Remember that the SC's diff locks input torque to both wheels evenly when one axle shaft spins at a (non trivial) different rpm from the other. The basic purpose of any diff is to allow the rear wheels to spin at slightly different rates when turning. The purpose of a locking diff is to make sure the power goes to both wheels when needed.

    Ken

  7. #7
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    Feb 2003
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    Here's a really good old video describing how the differential works

    https://www.youtube.com/watch?v=yYAw79386WI

  8. #8
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    I always do it with the car on the ground and the center cap out. Pop it in when im done.
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