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  #11  
Old 11-02-2010, 11:05 AM
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Based on the work you've done I'm going to assume all of the front end components are in good shape, including your leaf spring bushings. Even if they are new, you have to make sure they are the right size and don't let the thru bolt have any slop. Also make sure your u bolts are tight.

It doesn't sound like axle wrap to me, but it definitely sounds like torque steer.

On my SOA 40, under hard acceleration, it leaps to the left until you shift or let off the gas, then it it shifts back to the right until you hit the gas again, then it leaps back to the left again. Thats with a 2F, with your 5.3 you're putting out a lot more HP which probably makes it even worse.

I do have a trac bar so I know it's not axle wrap on mine. Also, on leaf spring vehicles, when you increase the ride height and/or add softer springs you increase the odds of changing the suspension geometry. When you accelerate the entire body/frame has a tendency to rotate in a clockwise manner (viewed sitting in the drivers seat) because of the engine torque being transferred. Taller suspension components have more leverage and typically give you more flex. As the weight shifts towards the passenger side that spring will flatten (lengthen) and the drivers side will raise (shorten) which has the effect of turning the solid axle ever so slightly towards the drivers direction. Thus the pull to the left. Thats why it is important you have no slop in your spring bushings. This suspension shift is made worse by the torque steer caused by the locker. The torque steer is one of the unfortunate effects of the lunchbox style lockers.

I have another rig with a Detroit Locker in the rear and the torque steer is present but virtually nil with that unit. With an ARB unit there is zero torque steer when it's unlocked, but the downside is the higher cost for the Detroit or ARB.

If you can add a sway bar to your suspension it will help reduce some of the body rotation but you won't get rid of the torque steer completely unless you change lockers.
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  #12  
Old 11-02-2010, 01:04 PM
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Strange that Marco doesn't have that problem, though, seeing as he has a V8 in his truck too. Did you drive Marco's truck to make sure he's not "not-feeling" something you feel? Or that he's not lying to you?
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  #13  
Old 11-02-2010, 01:49 PM
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Yes, it is a 62, sorry for not clarifying.

I thought the thrust angle would cause it to move one way or another all the time, not just under acceleration. Whatever the issue is, keep in mind that sitting still, or coasting I should say, all is fine. It only is an issue when power is applied to the rear wheels.

I have driven his and I didn't notice it, but he has ARB lockers instead of the Aussie I have, so maybe he would experience it if he did. He said he used to have aussie in the back though, and there's no way he wouldn't have noticed it. By pulling the steering wheel, I mean the steering wheel is at the 3 o clock position when accelerating to overcome the pull.

All bushings are new. The lift was just put on about 2 months ago.

I rechecked my caster and it looks like I have 0 on the PS and 1-2 degrees on the DS so I'm going to add some shims tonight and see what happens. Not sure how I am off from when I checked it 2 months ago (still post lift).
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Old 11-02-2010, 01:55 PM
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Trey's pulls much worse than mine did when I had the Aussie. I drove it and it is literally all over the road. Feels like mine did when the caster was not steep enough, but is amplified.
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  #15  
Old 11-02-2010, 02:02 PM
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How do you measure caster without a fancy alignment table?
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Old 11-02-2010, 02:04 PM
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I just put an angle finder on the knuckle at the knuckle bolts. Same with measuring pinion angles and such.
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Old 11-02-2010, 02:51 PM
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This is certainly not axle wrap. Likely torque steer, or roll steer, like randy suggested.

What angle is your drag link at? Likely not the cause but extreme drag link angles can cause issues.

Get the caster fixed. That cross caster will hose you a bit, but not a ton. Is positive good on these trucks?

I have some roll steer in my truck due to the rear link design. With leaf springs, you have a similar issue with roll axis, but it isn't as pronounced.

As for vibration, perhaps the locker isn't functioning properly? Did your drive shaft come apart and possible the joints are out of phase now? I'm guessing you and marco checked out the bearings before sticking it in. You should have no play in the pinion flange.
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  #18  
Old 11-02-2010, 03:01 PM
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My drag link is not anything extreme I don't think. It is angled down so there is a bit of bump steer, but it is the same angle anyone with an OME lift would have.

I'm doing 3 degree caster shims tonight so I will post up afterwards how that helped out. From what I understand, 1* of caster (top of knuckle 1* towards the rear) is stock, but that many people run 4-6* without issues.

My understanding is that there is no real bad effects on steering to be anywhere from 2-9* or so. More than that supposedly can induce the death wobble, and obviously the more caster you have, the more effort you have to use to move the wheel from center. Also, you don't want to go so far that you throw the pinion angle off.

I'm not sure yet on the vibration. It was a used diff, but Marco and I looked at it and he didn't seem to think there was any excessive play in it. Once I get my steering figured out I will probably pull the locker and leave the diff and see if it still has issues just to isolate which of the items is causing the problem.
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  #19  
Old 11-02-2010, 03:46 PM
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The caster correction should help but it will not eliminate torque steer. You get that from the body roll and the fact the locker is applying more power to one wheel than the other for a short period.

Be sure and check your front cross member to make sure it is not loose or cracked. If it is it will allow the front to flex more exxagerating the problem.

As far as the diff causing vibration on decel. The first thing that comes to mind is what Ike suggested, DS out of phase (though it should also cause vibration on acceleration too). Next likely would be a bad pinion bearing. When you accelerate the torque forces the bearing into the cup removing slop, but when you decel it pops it out of the cup if there is excessive play. That can let the flange wobble a little but it has to be really worn. The other possibility is the locker is locking/unlocking causing wheel hop or jerking. If you pull it as a test you'll answer that question fast enough.

I don't believe any of your issues are related to the placement of the TC in relationship to the diff pinion flanges. I have seen people run toyota TC's set up for offset differentials and run them into a centered diff. The only issue they ever have is premature u joint death. There is enough travel in the DS slip joint to ensure any TC movement is not being transferred to your front axle.
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  #20  
Old 11-02-2010, 05:40 PM
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Good thoughts, I'll look at it tonight.

As for the driveshaft, it is not out of phase. I did disconnect it from the diff to change it out, obviously, but I didn't pull it apart, and I also looked at that again last night to make 100% sure and the yellow dots from when it was balanced and shortened (5.3 conversion) still line up on the yoke and the shaft.

that's good to know that being off center from tcase to diff will not cause an issue as that was one of the main things I was looking at.
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