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U Bolts Torque Value

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by Rideandrepair, Aug 25, 2020.

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  1. Aug 25, 2020 #1
    Rideandrepair

    Rideandrepair Road Train Member

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    2000 Freightliner Classic. Anyone know what the proper torque for new U Bolts on the rear drive axle, to get proper stretch. Any special procedure? Only changing one set,(2) on left rear drive.
     
    Rideandrepair, Aug 25, 2020
    Rideandrepair, Aug 25, 2020
    #1
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  3. Aug 25, 2020 #2
    AModelCat

    AModelCat Road Train Member

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    Depends. What suspension are we dealing with?
     
    AModelCat, Aug 25, 2020
    AModelCat, Aug 25, 2020
    #2
    Rideandrepair Thanks this.
  4. Aug 25, 2020 #3
    Rideandrepair

    Rideandrepair Road Train Member

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    Airliner
     
    Rideandrepair, Aug 25, 2020
    Rideandrepair, Aug 25, 2020
    #3
  5. Aug 25, 2020 #4
    BoxCarKidd

    BoxCarKidd Road Train Member

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    You can Google that by U-bolt diameter. Yours are probably 7/8's. A 7/8's open end wrench will loosely fit over the bolt. Those torque to around 480 FT LBS off the top of my head.
    Most people do not have a torque wrench for that. Buy a torque multiplier or swag it.
    One hundred foot LBS is equal to 100 pounds hanging on a one foot long wrench at a 90 degree angle. While that probably does not really help you much a four foot pipe on a ratchet pulled 100 foot pounds works out to around 480 ft lbs. We do not normally use a torque wrench on them but use one to check what we are doing occasionally. They kind of come to a tight spot with four and a half feet of total pull. Stop there and recheck them a month later.
    There are exceptions like some Macks with grade 8 u bolts. Rechecking is probably more important than being at the exact torque spec.
     
    BoxCarKidd, Aug 25, 2020
    BoxCarKidd, Aug 25, 2020
    #4
    spsauerland, tommymonza and Rideandrepair Thank this.
  7. Aug 25, 2020 #5
    Shawn2130

    Shawn2130 Heavy Load Member

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    I’m about to do u-bolts tomorrow as well.

    freightliner airliner too.

    Now I don’t have to look up torque specs as it already showed up here. Thank you guys. :cool:

    18E9FBC8-CEB9-4B86-88D3-562718830EBD.jpeg

    The U-bolts have come loose and the spring (I think) has dropped or twisted causing the air bag to look crooked.
     
    Shawn2130, Aug 25, 2020
    Shawn2130, Aug 25, 2020
    #5
    Rideandrepair Thanks this.
  8. Aug 25, 2020 #6
    Rideandrepair

    Rideandrepair Road Train Member

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    Thanks for the rule of thumb tip. I’ll use the 4’ cheater. Then after I get rolling, have the Truckstop use their tire torque wrench on it. I’ve seen them use it for U bolts. That makes sense. I have a broken shock mount, to replace, so I got it and new U bolts.
     
    Rideandrepair, Aug 25, 2020
    Rideandrepair, Aug 25, 2020
    #6
  9. Aug 25, 2020 #7
    Rideandrepair

    Rideandrepair Road Train Member

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    That’s how mine looked when the torsion bar mounting ear broke, U bolts never loosened up, good time to inspect and change the torsion bar(s) if needed. I guess you know, U bolts are a one time use item, once they’re stretched when properly torqued, they supposedly can’t be re used, because they won’t stay tight. Good luck, lining it up. We used a bottle jack, along with floor jack on mine, when the torsion rod ear broke. It can be done that way, one at a time. But if you’re doing them all, with torque rod disconnected, I guess it doesn’t matter. I’m Leary of dropping the whole axle, and lining it up. If you have the means though, probably best. Good Luck.Be safe.
     
    Rideandrepair, Aug 25, 2020
    Rideandrepair, Aug 25, 2020
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  10. Aug 25, 2020 #8
    BoxCarKidd

    BoxCarKidd Road Train Member

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    You surely know you have something else going on there. Normally a pin between the axle housing and spring or bracket maintain alignment. You need you look a little deeper while you are working on that.
     
    BoxCarKidd, Aug 25, 2020
    BoxCarKidd, Aug 25, 2020
    #8
    spsauerland, Rideandrepair and Shawn2130 Thank this.
  11. Aug 25, 2020 #9
    Shawn2130

    Shawn2130 Heavy Load Member

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    Yes, I’ll be taking it apart to see what’s wrong.

    All the other bags are straight and good.

    Truck only has 405,000 kms on it.
     
    Shawn2130, Aug 25, 2020
    Shawn2130, Aug 25, 2020
    #9
    spsauerland Thanks this.
  12. Aug 25, 2020 #10
    Rideandrepair

    Rideandrepair Road Train Member

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    Looks like a new air bag. Maybe it’s installed wrong. They have dimples on the top that align with the bracket, and a lot of wiggle room for adjustment. That’s looks pretty extreme though. Was the old one that way?
     
    Rideandrepair, Aug 25, 2020
    Rideandrepair, Aug 25, 2020
    #10
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