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why cut and turn the knuckles

Discussion in '40- & 55-Series Tech' started by bad_religion_au, Sep 17, 2003.

  1. bad_religion_au

    bad_religion_au

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    why when doing a spring over do you cut and turn the housing, i am aware it's to get the pinion pointed towards the tcase, but couldn't you turn the whole axle as one piece, and just run the knuckles at the angle?

    don't wish to step on toes, just want an explanation, as there is bound to be one, i just couldn't think of one
     
  2. theo

    theo

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    To maintain caster.
     
  3. bad_religion_au

    bad_religion_au

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    knew there'd be a reason. thanx
     
  4. rusmannx

    rusmannx

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  5. woody

    woody Internet Fireman Staff Member

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  6. dd113

    dd113

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    Bascially, what happens is that the wheel will be inclined forward because you moved the springs up. The smaller the lift and tire the less you will notice this on the road. You can end up with bump steer and the truck will wonder all over the road. Sort of dangerous. Same thing happens with spring and shackel lifts although it is much worse on shackle lifts. Shims will fix of help fix castor issues but you can only go so far. About 4 degrees is it. By cutting the knuckles you rotate them back to their "original" position relative to the ctr line of the axel.
     
  7. Jackson

    Jackson

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    [quote author=dd113 link=board=1;threadid=5351;start=msg42132#msg42132 date=1063814493]
    Bascially, what happens is that the wheel will be inclined forward because you moved the springs up. The smaller the lift and tire the less you will notice this on the road. You can end up with bump steer and the truck will wonder all over the road. Sort of dangerous. Same thing happens with spring and shackel lifts although it is much worse on shackle lifts. Shims will fix of help fix castor issues but you can only go so far. About 4 degrees is it. By cutting the knuckles you rotate them back to their "original" position relative to the ctr line of the axel.
    [/quote]

    Excellent explanation - thanks.
     
  8. Slowerthanu

    Slowerthanu SILVER Star

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    When I eventually do my front spring over, I am going to cut and turn more for the improved caster than the pinion angle since my front end is pushed forward 4 inches over stock, When I do a Toybox I am going to be looking at a 40 inch front shaft. The pinion will not be pointed up very far at all.
     
  9. theo

    theo

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    [quote author=dd113 link=board=1;threadid=5351;start=msg42132#msg42132 date=1063814493]
    . . . You can end up with bump steer . . .[/quote]

    Actually, bump steer is a different beast. It occurs if your drag link is many degrees out of parallel with your tie rod so that when one wheel travels up over an obstacle or down into a depression, the angle between the link and the rod changes and pushes or pulls the tie rod (and wheels) sideways. Kind of like collapsing or stretching two legs of a triangle.

    Castor causes the entire front of the vehicle to raise up slightly when you turn the wheel. Then there is a gravity-driven tendancy for the wheels to return to straight ahead when you release the steering wheel. (At least that's my simplistic understanding so far. There's lots more complexity but I haven't tried learning it.)
     
  10. sdgraber

    sdgraber

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    Just listening in...that was a helpful desription and visual on bumpsteer and caster...I'm doing a SOA with on my 40 and that clears a few things up...thanks

    Scott
     
  11. hendo

    hendo

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    i think if you dont have a way to make sure your axle is straigth have a pro cut and turn your axle its pritty cheap but you know its done right alot depends on the welds of your axle ends,try calling jmr 805 584 0191 hes doing mine ask for jim