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  1. #41
    Clod Hopper's Avatar
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    Quote Originally Posted by Scott@Rockstomper
    Anyway, back to the DW, this calls for more info on kingpin inclination too--changing wheel backspacing can impact DW, because the contact patch is (ideally) relative to kingpin inclination (which is a generic term that applies to all steer axles, regardless of the actual pivot joints used). I'm curious as to what the kingpin inclination is on a newer D30 (or a balljoint 60) relative to some of the older stuff, and all of that could be relevant to why some axles DW under certain rigs, but not under others.
    You talking camber here? yeah, backspacing affects the scrub, turning angles and issues with camber. I don't see it doing much to caster. But definitely wheel spacing affects DW. A stock vehicle can be fine, but put on aftermarket wheels with less backspacing and suddenly DW is a problem. I found this on my XJ. Put on the 4.5" lift, no real problems running the stock wheels and tires (aside from the looks I got from others), but swapped to aftermarket wheels and bigger tires, I crossed the threshold and started wobblin'.

    wobblin'......

    Just now realized I shoulda called the truck the "wobblin' goblin". I just never think of the good stuff when it is appropriate.
    Proudly un-offended.

  2. #42
    Tube Monkey Scott@Rockstomper's Avatar
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    Quote Originally Posted by Clod Hopper
    You talking camber here? yeah, backspacing affects the scrub, turning angles and issues with camber. I don't see it doing much to caster. But definitely wheel spacing affects DW.
    Nope, not camber (hopefully with a straight axle, we don't need to worry about it, but for the IFS/IRS crowd, it definitely does matter too), but the angle that the steering pivots around that looks like a big A when viewed from in front. Normally, that pivot axis, extended through the ground plane, passes through some part of the contact patch, for the sake of reducing scrub, and is therefore impacted by tire height, tire width, wheel offset, and a few other things as well.

    Knowing that we can't really change kingpin inclination without changing axles, I'm curious as to if there's a "break point", such that, above a certain tire size, you have to go to a different axle (for the different kingpin inclination) to even have a decent chance at beating DW.
    Thanks to: United Four Wheel Drive Associations and Stay the Trail Colorado, for their support of all of us and the sport in general.

  3. #43
    Clod Hopper's Avatar
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    Quote Originally Posted by Scott@Rockstomper
    but the angle that the steering pivots around that looks like a big A when viewed from in front. Normally, that pivot axis, extended through the ground plane, passes through some part of the contact patch, for the sake of reducing scrub, and is therefore impacted by tire height, tire width, wheel offset, and a few other things as well.
    still sounds like camber. I guess I need a picture.

  4. #44
    Captain Radon Steve's Avatar
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    Quote Originally Posted by Clod Hopper
    Just now realized I shoulda called the truck the "wobblin' goblin".
    Hittin' the bottle again, huh Chip?

    Quote Originally Posted by Scott@Rockstomper
    Knowing that we can't really change kingpin inclination without changing axles, I'm curious as to if there's a "break point", such that, above a certain tire size, you have to go to a different axle (for the different kingpin inclination) to even have a decent chance at beating DW.
    I don't think you have to go to larger axles/different kingpin inclination with larger tires to "beat" DW when everything's new and tight, but if you want to keep it at bay for any length of time that's probably true. 40" TSL/SXs on a D44 shouldn't have DW if everything is tight and it's set up correctly. However, it will certainly cause much faster wear on all of the front suspension components than the same tires on a kingpin D60. So, you're more likely to develop DW sooner with big tires/small axle than big tires/big axle.

    You're right tho Scott, less backspacing and larger tires certainly make the entire suspension system less stable, putting you closer to DW.

    Anybody heard of anyone running Mog axles complain about DW? Maybe that's the real solution.

    BTW, I did have to adjust the camber on my front EB D44.

  5. #45
    Clod Hopper's Avatar
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    Quote Originally Posted by Steve
    Hittin' the bottle again, huh Chip?
    Nope. Refer to post on hangovers in the chitchat. Maybe too many mountain dews, m&ms and christmas cookies? I am a jittery mess this time of the afternoon.



    Quote Originally Posted by Steve
    BTW, I did have to adjust the camber on my front EB D44.
    did you do that with a shim behind the spindle? Offset ball joint? Vertical housing massaging with granitic impacts?

    is it the D50 that has the weird double cam adjuster to reset caster and camber?

  6. #46
    Captain Radon Steve's Avatar
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    Quote Originally Posted by Clod Hopper
    did you do that with a shim behind the spindle? Offset ball joint?
    Shims. When I built the axle a few years ago I found this "spacer thingy" behind the spindle. Took it off. Put it back on after installing the locker, alloy shafts, etc. Tire leaned WAY in at bottom. Took it to an alignment shop and paid the guy to take it apart and reinstall shim correctly. He took the time to school me on solid axle camber adjustment. Lesson learned.

  7. #47
    Tube Monkey Scott@Rockstomper's Avatar
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    Quote Originally Posted by Steve
    Anybody heard of anyone running Mog axles complain about DW? Maybe that's the real solution.
    No, but I have heard a number of complaints about Mog axle camber (it's actually significant), and a similar number of complaints about Mog axle top speed (50-ish, and IIRC, extended travel at that speed necessitates periodic cooling-of-the-portals stops as well).

    Perhaps below 50mph, DW is less of an issue?

  8. #48
    Clod Hopper's Avatar
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    Quote Originally Posted by Scott@Rockstomper
    No, but I have heard a number of complaints about Mog axle camber (it's actually significant), and a similar number of complaints about Mog axle top speed (50-ish, and IIRC, extended travel at that speed necessitates periodic cooling-of-the-portals stops as well).
    I don't see why mogs would be exempt from caster requirements. Geared as low as they are, I can see top speed limits and heat generation. Inside those hubs is alot of spinning gears and not that much lube volume to dissipate heat.

    Quote Originally Posted by Scott@Rockstomper
    Perhaps below 50mph, DW is less of an issue?
    Usually hear 40 - 45 mph as the edge of DW hell. Different for different rigs, of course, I have heard problems as low as 30mph. But 45 is a common threshold.

  9. #49
    Tube Monkey Scott@Rockstomper's Avatar
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    Quote Originally Posted by Clod Hopper
    I don't see why mogs would be exempt from caster requirements. Geared as low as they are, I can see top speed limits and heat generation. Inside those hubs is alot of spinning gears and not that much lube volume to dissipate heat.
    Nono, camber. The tires, looking from the front, are out on top, in on the bottom. Wears the tires funny unless you have tons (literally) of weight on them (in which case, it wears the tires faster, but evenly). Much more so than any other straight axle rig I've ever seen.

    AFAIK, Mog caster is roughly normal, relative to other stuff out there, just a couple of degrees.

    As a sorta-devils-advocate question... how come stock Scouts don't have DW with zero caster? (inability to exceed 30mph in stock form disregarded)

  10. #50
    Clod Hopper's Avatar
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    Quote Originally Posted by Scott@Rockstomper
    Nono, camber. The tires, looking from the front, are out on top, in on the bottom.
    whoops. Never realized they had weird camber, but that does explain why some pics of mog axles looked funny. just chalked it up to perspective issues.

    Quote Originally Posted by Scott@Rockstomper
    As a sorta-devils-advocate question... how come stock Scouts don't have DW with zero caster? (inability to exceed 30mph in stock form disregarded)
    Scouts are on leaf springs right? From what I have gathered, leaf sprung fronts are less prone to DW. As are radius arm setups. The stocker ford system is almost anti wobble with the big C-bushings on the axle. That is what I have under my XJ now, no stabilizer or anything. Never a wobble, shimmy or anything. Very stable.

    The majority of DW compaints I have run across are the typical 4link and a trackbar with coils type frontends. Course my experience my be biased based on the vehicles I tend to deal with. I don't spend much time in scout, cj and similar forums to know how much DW is a problem for them or how they overcome it.
    Last edited by Clod Hopper; December 7th, 2005 at 05:00 PM.

  11. #51
    Tube Monkey Scott@Rockstomper's Avatar
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    Flexier suspensions tend to be more prone to DW than stiffer ones--I think that's where the leaf spring thing comes to play. EB's are notorious for DW issues, once they get flexy--in stock form, about the only thing that can make DW show up is ball joints nearly falling out.

    Gonna make me read a whole lot more of the Milliken book than I ever intended here... not that it's a bad thing (it's well written and interesting) but there's a lot of it there.

  12. #52
    Thanks guys! Great post!! Alot of it was way over my head but I think I have an idea where to start. I have had death wobble that keeps getting worse and worse and no time to hook up with someone to fix it. Thanks again!
    "As you move through this life and this world you change things slightly, you leave marks behind, however small."― Anthony Bourdain

  13. #53
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    Ok guys, did a little digging tonite. Lord of the Rings was on but not much else, and it was too cold to work on the jeep. So I surfed around Pirate and did a little digging. Here is what I found:


    • Caster on rear steer is primarily unnecessary. No real explanation on this, but the guys running it seem in agreement. From JR:” There's no reason for any caster with full hydro as the rams don't care about any small amount of steering input that caster could give. Run it straight-up.” Coyote11 provides: “I did a search and found that Jason Paule builds them with zero castor in the rear steer application.” Elfcruiser responds: “It will turn easier with 0 caster. Other than that, if you're not using it at speed on pavement, it won't matter too much a few degrees one way or the other.”
    • Some have suggested about 2 deg for no real reason other than to account for any slop in the system. From Stazworks: “I definatly agree that some caster in the rear is good, if it was set at 0 deg. it would cause premature wear of linkage. There is always some tolerance of slop in a system so if it is set at zero the wheels will chatter back and forth till it becomes noticable. It may take a long time to notice this unless you see some speeds once in a while.”
    • Full hydro rear systems that have no bushings (all hard items like hiems and such) will no likely be subject to DW. Essentially, there is not typically enough slop in the system to allow it to start. Course it is important to replace worn steering components.
    • Interesting suggestion from Station: “One advantage to having rear caster is that you can program some lean of the tires when they are steered. This can make them turn just a bit sharper , and can combat tire roll. This is something alot of people don't consider at all when thinking caster angle. Even with negative caster your front steering can still have good self centering characteristics , but the tires will lean out on corners like a Wino on a bicycle and cause the tires to roll really bad. I have witnessed one case of this that was so bad that on a 44" swamper the rim would almost touch the ground when steering while moving on smooth flat ground at road pressure.”
    • With regard to rock crawling (not street driving), JR continues with: “From a rock crawling standpoint, it has been discussed to use a lot of positive front caster, like 10 or more deg. The idea being that the front tires flop out and grab more into the rocks on the side when they are turned. On the rear, the same applies only opposite, a lot of negative caster. I have positive caster on the rear and hate it. On steep up hills, the effective wheel base seems to get shorter when the wheels are turned and makes the car easier to roll ( well, it does for me).” Station responds: ” I agree with this logic. I am running (I guess I should say rolling around instead of running somewhere around 6* of caster front and rear. Obviously positive in front, and negative in rear. This gives the tires a nice lean into corners which gives the bicycle effect that makes the vehicle steer sharper due to an arc shaped contact patch on the ground. My 120" wheelbase buggy ,as it sits, turns ALOT sharper with just front steering than my 95" wheelbase , F/R ARB'd TJ does. Mostly due to the awesome steering angle of the mogs , but I do believe the caster helps it out an appreciable ammount.”
    • With regard to using rear-steer in a DD, RedBullJeep had this to say: “even a tiny amount of play in the rear steering can cause havoc. The front end is being pushed and your caster takes care of any play (in theory). The rear is DOING the pushing and caster will do nothing to help you if there is any play anywhere. The RockIt gets squirrly after about 15 MPH. If I pin the rear-steer, then 35-40mph is acceptable but then if it's pinned, the use of rear-steer is gone. Yes, you can make a tight rear steer setup, but one little problem on the trail or road will change that very quickly. I recommend against it.”
    • There is thought about how rear caster interacts with front. Tony K gives “Remember that with caster, the tire "lays" over a little when turning. Sometimes this helps in the front by decreasing the contact patch area and increasing the lbs per square inch you have remaining.” Then Redrangie added “That's exactly right. Think of it as the "quickness" of the steering. I would put your rear caster at equal or less than your rear, or you will have bad oversteer, not too noticeable at slow speed, but a drag for keeping your line. Since the rear is most LIKELY being set up to "help" the front, I would make it at zero or thereabouts.”

    Alot of the provided information is more directed at issues related to rock-crawling, but some has to do with riding on the street. The more detailed info came from threads which had more to do with the steering system and return to center hydro systems. Ironically, Scott popped up in many of them, so it is possible that I am not providing anything new here, other than collecting it to one place.

    Basically what I put together is although caster is not important, it cannot hurt to run some minor caster, which can help if the steering system becomes loose from wear. Also, some toe in is important.

    Does any of this help or spur other questions?
    Last edited by Clod Hopper; December 7th, 2005 at 09:20 PM.

  14. #54
    Captain Radon Steve's Avatar
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    So I guess when I said this:

    Quote Originally Posted by Steve
    I suspect you'd still want some positive caster to help them return to center easier, but since you probably have full hydro rear steer, that's not an issue. Since the rear axle is "trailing" instead of "pushing," my gut feeling is that anything a few degrees either side of zero would probably work fine.
    on page 1 of this thread I was essentially correct?

  15. #55

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    SAI is basically a caster like angle, though viewed from the front. On a strut system your points of register would be the center of the upper strut bearing and the lower (only) balljoint. It's a number normally pulled only on days like today, where we're analyzing a car to see what that curb shot did.

    As said above, the more the caster the more the camber will change when turned. Caster also provides a lifting force, that's why it increases stability to a point. When the wheel turns the chassis rises, and the countereffect is to keep the wheels straight.

    Scott.. excellent point re: too much caster causing horizontal oscillations. I can pull some SAI/IA numbers on Super Dutys if it'll help.

    Scrub radius has a big effect too. An XJ with the most violent wobble I've seen was cured by putting the wheels out another 5/8 per side.

  16. #56
    Clod Hopper's Avatar
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    Quote Originally Posted by Steve
    I was essentially correct?

    But Steve, you are ALWAYS correct! No one ever doubted that!



    (geez, how does he walk through doors with a head that big?)

  17. #57
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    Where was this thread 6 months ago!!!!! I JUST ( as in 3 days ago ) finished my 6 month battle with DW. This would have helped out a lot.

  18. #58
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    Quote Originally Posted by WhtJeep
    Where was this thread 6 months ago!!!!! I JUST ( as in 3 days ago ) finished my 6 month battle with DW. This would have helped out a lot.
    Hey Steve (well really Eric, but I know Steve is reading this...) I know the idea of a tech area has been bantered about in the past. Any new thoughts on this? A list of links to the "better" threads organized by topic?

    Just reviving a random thought......

  19. #59
    Your what hurts? Shifty's Avatar
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    Steve,

    I am not real familiar with the measurements/angles and such that go into an alignment. When a shop like Firestone does your alignment they just set it to "factory specs", correct? I guess what I am shooting at is that I run a 2" lift on my TJ with 31's , and still have what you labeled as a decaying respone. I wrote it off as nothing more than the after shocks of a bout of serious DW until I read your post. I have done all of the suggested "cures" for the DW (new steering stabilizer, tighten up the front-end, alignment, balance, blah, blah, blah) How could one calculate what specs the caster,camber, toe, thrust, etc. should be at to compensate for the change in the dynamics of the front end? Very informative write-up. Thank You.

    Rob
    I'm robbing a bank because they got money here. That's why I'm robbing it. -Sonny (Al Pacino)
    http://www.coloradocarry.com/forums/...referrerid=528 For the love of CCW

  20. #60
    I am new to this forum and a google search landed me here. I have a 96 Cherokee Classic with 236,000 miles. Just had the original shocks replaced. Now i get the "Death Wobble" especially when hitting bridge joints that are angled on a highway overpass(WOW) it wobbiles. I am guessing from what I am reading I should replace the trac bar. Can i do this myself or does the vehicle need to be lifted. And once that is done, do i need a wheel alignment?

  21. #61

    red neck fix

    I have had death wobble on several axles under my jeep. The problem is, we think it should act some what decent on the road after running INdy. I have not had a lick of death wobble since installing a red neck Hydro assist ram. Now I also do all my own alignments and set at an 1/8th inch toe-in so there is some error in it.

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