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Cross Over Road Characteristics

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by DPI, Oct 17, 2001.

  1. DPI

    DPI 1/2 ton status

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    I installed my cross over and now I am noticing some weird road manners. When I hit a dip in the road it wants to move my steering wheel a little. Does any one else have this, and is it normal? It did not do this before the cross over. I would not call it bump steer, but it is similar. I am thinking it is from the weak Chevy frame moving a little where the shackles are located. There is a a lot of movement in the shackle bushings and frame area arond the shackle mounts when the steering wheel is turned side to side while not moving I have the ORD shackles and bushings installed. I would like to know if this is normal. I am moving my axle forward 1.5" so this may git rid of some of the problem on the rear spring bushings since there will be less leverage on them.

    4.56 Geared, Power Locked, Dana 60
    4.56 Geared, TSM Disc Braked, Detroit Locked, Corporate 14
     
  2. JST12

    JST12 1/2 ton status

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    Here is my thinking on this... The axle wants to move straight up when you hit a dip with both front tires. The cross-over drag link is connected at an angle downward. As the axle wants to move up, the draglink wants to move in an arc. This would either push the axle sideways (in the same arc) which is unlikely, or push the pitman arm and thus steering wheel the opposite way. The way to correct it is using a drop pitman arm which provides a draglink parallel with the ground, or add a track bar which forces the axle to move in the same arc as the draglink. Just my thoughts. See ya. JT
     
  3. Zepplin

    Zepplin 1/2 ton status

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    I don't know if this will solve it but, I would recommend purchasing the steering box brace. Maybe the frame is flexing too much. Give Stephen a call.

    74 Blazer
    Zepplin
    Check out my Blazer
    [urlhttp://community.webshots.com/user/zepplin1976[/url]
     
  4. DPI

    DPI 1/2 ton status

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    I have the brace installed. I think I have bought at least one of everything stephen has manufactured, except the doubler.
    I do think it is in the frame flexing somewhere. I am just not sure where. My guess is where the rear shackles mount to the frame.

    4.56 Geared, Power Locked, Dana 60
    4.56 Geared, TSM Disc Braked, Detroit Locked, Corporate 14
     
  5. ZZ4x4

    ZZ4x4 1/2 ton status

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    If you hit an even dip with both front tires (not a pot-hole) and the wheel moves the same way each time and then back to the center,it is not your frame flexing and the brace won't help here. This is a common occurence with steering geometry issues. I have dealt with this over the years on several trucks and always fixed it by moving the pivot points ( dropping the pitman arm, or for track bar trucks, moving the mounting position) Look under the truck and trace the motion of your linkage vs the springs. Are you using a dropped pitman arm? JT (formerly JST12)
     
  6. DPI

    DPI 1/2 ton status

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    Yeah, I am using the drop pitman arm. You described it correctly, and the steering wheel only moves slightly. But when I first felt it, it kind of caugt me by suprise. Do you have any ideas of how to correct this since I already have the dropped pitman arm?

    4.56 Geared, Power Locked, Dana 60
    4.56 Geared, TSM Disc Braked, Detroit Locked, Corporate 14
     
  7. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    I think the only way to help what you describe is to make sure the pivot points (the tie rod ends) are level. As long as one is above the other, you will have this sort of thing, it is just not NEARLY as pronounced as it is on a non-x-over rig (which has a shorter radius due to short drag link). Technically, even with the pivots perfectly level you would get some feedback like this since it is still moving on a arc due to one end being vertically stationary and the other moving vertically (or more accurately, moving vertically with respect to each other). Something has to give. Beyond that, you would need a panhard rod to force the axle to move in the same arc as the x-over link, which, in turn, leads to different issues with suspension bind (particularly with articulation). Other than trying to make the pivots as level as possible (without too much trouble) you are getting well past the point of diminishing returns.

    Bad Dog

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  8. kchecca

    kchecca Registered Member

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    Does your truck have a track bar installed? It goes from the axle on one side to the frame on the other. It should be parallel to the steering drag link.

    It basically causes the axle to shift to the side during flex, which sounds bad, but in fact will be better since you wont get that steering wheel bounce.

    If there is no track bar, the best thing to do is make your drag link as level as possible.

    --------------------------
    Keith C
    Bigbird '00 Jeep TJ
    Grandpa's '77 Blazer
     
  9. DPI

    DPI 1/2 ton status

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    OK, this is making a ton more since. I guess I can live with this, and like I said it is not that bad, especially with the increased steering ability. My rockstomper drag link has a 4.5" drop in it, I think that will be as level as it gets. I may look into adding a track bar for more stability.

    4.56 Geared, Power Locked, Dana 60
    4.56 Geared, TSM Disc Braked, Detroit Locked, Corporate 14
     
  10. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    A dropped drag link only helps the angles at the ball joint (tie rod end) to keep it from binding. It does absolutely nothing to fix bump steer. You have to get the pivot points (in this case, the tie rod ends) to be level in order to minimize it (not eliminate it). Remember, the arc is defined by the radius from one pivot to the other. Bending the line between them has no affect at all when determining the arc. To change that, you would need a dropped pitman arm or a raised steering arm on the pass. side knuckle. X-over will not eliminate bump steer completely although, by increasing the radius of the arc, it does dramatically reduce it (all other things being equal). The main purpose of x-over (other than *reducing* bump steer) is to allow full range of steering while twisted up.

    Just a guess but, I suspect that your original steering setup (before x-over) had the ends relatively level so you would see little bump steer (no worse than factory) but loose almost all steering when the driver's tire is stuffed or drooped. The x-over, with bent link, seems worse because of the exaggeration due to the preset (at rest) angle on the link.

    Also, be careful with the trackbar/panhard idea. This opens a whole can of worms including frame breakage and suspension binding while articulated. These issues are VERY non-trivial. Stephen (quite capable in anyone's book) at ORD even ran into many serious problems trying to make this work right on his rig. That is one of the reasons leading him to ultimately go with 4-link and coils. Of course, this is getting so far over the the curve on past the point of diminishing returns that it is not very realistic except for the ultimate in hard core wheeling (re Stephen). If all your concerned about it a small amount of twitch, I wouldn't even consider anything more than dropped pitman/raised arm to get them as level as possible (within the limits of interference with other components).

    In short, IMHO, don't put too much time into it, it isn't worth the trouble.

    Bad Dog

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  11. Donovan

    Donovan 1/2 ton status

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    I think that we are forgetting one element. The X-Over Drag Link and the tie rod needs to be parallel to each other at rest. If they are not parallel you will get bump steer because when the axle move up in travel the axle moves back also. When it moves back the drag link will try to turn the wheel. Just something to think about.

    Donovan
    <a target="_blank" href=http://www.rustbucket.rockcrawler.com>www.rustbucket.rockcrawler.com</a>
    Got Leafs??
     
  12. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Good point, I had forgotten about the axle moving back as it goes up. Same principle, just a different plane. The vertical plane is generally the bigger problem due to lift, suspension movement, and articulation. However, if it starts out very far off of parallel in the horizontal plane then that could certainly exaggerate the effect.

    Bad Dog

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     
  13. BadDog

    BadDog SOL Staff Member Super Moderator Author

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    Hmmm, you know, it might be possible to even use that to some advantage. The passenger side is usually lower than the pitman arm, often resulting in a bent drag link like 90k5 has (needed to clear x-member too). When the axle moves up, that would push the pitman arm out, away from the frame, moving the wheel to the left (or causing the truck to turn right). In order to minimize this, the two pivot points need to be as close to level as possible but this is often (generally) not possible due to obstructions. Since the axle also moves back, it might actually be possible to (minimally) cancel some of that by having the pitman joint located ahead of the steering arm joint. This would be more trouble than it's worth since the only way (that I can see) to do that would be relocate the steering sector (not impossible, but likely not worth the benefit). Since the rearward movement is only a small fraction of the vertical movement, a significant offset (to move the pivot further along the arc where rate of change per unit of movement is greater) would be necessary to make an appreciable change. That much offset would itself cause additional problems. Oh well.

    Or, you could just modify/box/reinforce the frame, add a trackbar and four link, a couple of coil-overs, and call it a day. Oh wait, that is what Stephan and Steve Frizby (sp?) did. [​IMG]

    Anyway, just thinking...

    Bad Dog

    85 K30 CUCV, 350 TBI, TH400, 205, D60/C14, 4.56 Locked
    Some day: 4" lift, 44" tires, massive cutting, shorter wb and rear overhang.
     

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