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Death Wobble (FAQ?)

Discussion in '40- & 55-Series Tech' started by 90 Weight, Mar 6, 2007.

  1. 90 Weight

    90 Weight

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    Alright I noticed that there isnt anything in the FAQ about solving death wobble...and It seems like a common enough problem that maybe this could go into the FAQ

    Im looking for a list of all of the possible causes of death wobble. Having allready seached, it seems most of the threads are very specific to peoples vehicle.

    Thanks for any info.


    EDIT: HERE IS A LIST FROM THE FSM (THANKS IDAVE)

    wobble (Small).jpg
    wobble (Small).jpg
     
    Last edited: Mar 6, 2007
  2. Tankota

    Tankota

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    Anything associated with the entire front axle including steering, suspension, tires and wheels. That should cover it. ;p

    I haven't searched the FAQ but a writeup/list of how to go about fixing it along with stories of other peoples fixes would be a nice addition to the site.
     
  3. 90 Weight

    90 Weight

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    yea thats why I started this thread.


    Ok so I have read through some of the previous threads...thougth I would make a rough list of the stuff I know would possibly cause death wobble..and list the stuff I know is not wrong with my vehicle


    All of my bushings are NEW poly. so thats not a possibility

    My knuckles are freshly rebuilt (driven bout 10 miles on them) so thats out too.

    Any other axle related seals etc are all new (10 miles driven) so thats not a possibility,

    My wheels were recently ballanced...so that shouldnt be an issue.


    In my case I KNOW that the main cause...if not the only cause, is that I have done NO alignment. In fact just looking at the front of my vehicle, you can see the actually have a toe OUT rather than how they are supposed to be (toe in).

    If not just that, the only test drives Ive been on, I havent had shocks, so that probably contributes to it being wobble prone.



    If someone knows the specific toe that they should be adjusted to, that would be a good addition.
     
  4. SUMMIT CRUISERS

    SUMMIT CRUISERS SILVER Star

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    My 78 did this with recently balanced BFG Mud's. Got it up to about 50 and it scared the ___ out of me. I rotated them from front to rear and the death wobble went away. I believe one of the front tires was probably not in balance.
     
  5. bustanutley

    bustanutley

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    bent wheels is normally my problem. Not properly preloaded knuckles is very common, I preload mine to 20ft-lb as opposed to the suggested 8? in the FSM, but I run big tires. Worn spring bushings or anything in that connection. Wheel bearings not preloaded enough, once again I go over the spec. Tires are always a possibility, I run 4 golf balls in each of my tires for dynamic balancing.

    The ultimate band-aid => hydro assist :grinpimp:
     
  6. mmmahhmatt

    mmmahhmatt

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    on a skateboard we called them speed wobbles, & were common @ high speeds. usually if you tightened your trucks you could reach higher speeds before crashing...
    if there are any loose or worn components to the steering or front end of your fj it would be similar to skating w/loose trucks. but since everything is new & presumably tight, it's your lack of proper alignment. big tires like to follow every crack in the road, and a short wheel base makes it more noticable. (you can carve much faster on a longboard w/o speed wobbles.)
    i don't know proper alignment spec. on a 40, but you can use a tape measure to get close @ home. measure inside distance between front rims @ 3 and 9 o'clock and set to the same #. then get an alignment asap. it only takes a few miles to ruin expensive tires.
     
  7. Pin_Head

    Pin_Head

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    It is a combination of 1 or 2, + 3.
    1) Wheel alignment: Too little caster, too much toe in or toe out.
    2) Wheel/tire problems: out of balance, run out in wheel, out of round tire wheel.
    3) wear or slop in anything that locates the wheel. Frame crack, spring bushings, U bolts, tie rod ends, knuckle bearings, wheel bearings, drag link, center arm, relay rod, steering box.

    Since there are so many possibilities it is difficult to diagnose.
     
  8. 90 Weight

    90 Weight

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    Stoopid question alert: what is "caster?"

    is it the word used to describe toe in and toe out?
     
  9. mmmahhmatt

    mmmahhmatt

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    if toe in & out is level, camber is plumb. (level in a vertical direction.)
    negative camber=/ \
    positive camber=\ /
    or is it the other way around?

    ok, i checked myself. mabye caster refers to front axle degree as it relates to driveline angle- it may have changed with shackle reversal?
     
    Last edited: Mar 6, 2007
  10. KOOTENAY KRUZER

    KOOTENAY KRUZER

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    toe in refers to the wheels being closer together at the front than the back. toe out of course is just the opposite. camber refers to the wheel leaning in or out rather than being exactly vertica. caster refers to the kingpin angle leaning forward or backward from vertical. The kingpin angle on your 40 is the line between the center of the top and bottom bearings on your Birfield housing.
     
  11. Pin_Head

    Pin_Head

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  12. Strait Cruisin

    Strait Cruisin

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    Castor is the front/back angle of a line between the top and bottom knuckle bearings/ball joints. Not really set-able on a pig unless you use wedges between the spring and the axle but then you get to worry about drive line angles.

    Camber is the in/out angle of the same line.

    To in/out is the parallel planes of the wheels.

    Castor determines how well a vehicle tracks down the road, the further the bottom ball joint is ahead of the top, the more stable it is. Less castor is quicker steering but it wanders more. Castor has little effect on tire wear. Uneven castor values will cause a pull toward the negative value.

    Camber determines how the tire sits on the ground, tipping out or in. To much either way will take the rubber of the sides of a tire and will cause the vehice to pull toward the side with greater camber. Wear will be smooth though.

    Too much toe in or out will cause the greatest tire wear. Run your hand across a tire that has been scrubbing and it feels like someone has been working on it with a DA sander (which is about the truth). Most rear wheel drive cars run with an eight to a quarter inch toe in, front wheel drive cars about the same but toe out.

    You can ball park toe in with a tape measure. Just roll the vehicle back and forth a bit to relieve any tension and measure similar tread groves front and back. You can also jack it up and spin chauk marks on the tires. Chauk marks will also show you any out of round or wheel runout problems you may have too.
     
  13. F-junker

    F-junker

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    Caster: This is the measurement of the degrees in the steering axis. Your wheels turn leaft and right on this plane. Most think of this angle as being 90 degrees, but it does vary depending upon how the vehicle is set up. From the factory it should have about 1 deg positive caster. Think of these degrees of measurement taken from a circle with the very top being zero.

    When susupension mods are performed such as leaf srping lifts and shackle lifts, the original caster is often affected. The caster is a function of the mounting plates on the bottom of the axle and their position to the trunion bearings (knuckle bearings).

    BEFORE YOU REPLACE ANYTHING ELSE, CHECK YOUR CASTER ANGLE!!!!


    Generally speaking, when your lift a truck you will wind up with negative caster or another words the wheels actual steering into the ground in front of them as your driving down the road. That force exerted on the suspension causes vibration and bucking in the suspension. I mean to tell you it's freakin' scary when it happens and you don't know whats going on. I thought the truck was going to upend and flip!

    The easiest way to fix it is to use shims under the axle plates and get that positive caster back. Tom Wood's Driveshaft sells some realy nice steel shims in a variety of angles. I just ordered a set of 8 degree shims for my rear springs. I used 4 degree shims up front and got about 1-2 degrees + caster up front. that solved all of my problems up front so far. good luck and I also agree that a death wobble FAQ should be in place as I and many others probed this thing for a while here.
     
  14. agent orange

    agent orange

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    I recently traced the death wobble i get periodically to a worn ujoint at the steering box end of my steering column (better word...?). The top joint is tight but the bottom is worn out.
     
  15. 90 Weight

    90 Weight

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    im going to take the cruiser to the alignment shop trmow and have them set everything up... I actually dont have any shims under my axle....and its so bad I cant attach my front driveline...I assume a shop that does alignment will have shims and set it up properly...
     
  16. Tankota

    Tankota

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    Couple other things to think about.

    Friend of mine had all of his tires aired up to different amounts = death wobble. Aired them up evenly = no wobble.

    My steering box has alot of slop in it that I can't adjust out. Gonna have to replace it (probably with a YJ jeep box;p )

    Friend of mine had the wobble...turned out to be a cracked frame where his steering box mounted.
     
  17. IDave

    IDave

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    Toe In

    Forgive me if someone else answered this already and I missed it.

    The toe in should be 3-5 mm according to the FSM for an FJ40. This means that the distance between the center points of the two tires should be 4mm less in front than in back.

    I have read elsewhere that this determination is for bias-ply tires, and that for radials, a toe-in of "0" is correct.

    I would certainly fix the "penguin-toed" arrangement you describe.
     
  18. IDave

    IDave

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    Wobble

    A succinct list of causes and repairs from the FSM, most of which have been mentioned.
    wobble (Small).jpg
     
  19. 90 Weight

    90 Weight

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    Thanks IDAVE, thats exactly what this thread needed!
     
  20. Tankota

    Tankota

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    I'll add more thing...
    I can drive at ANY speed in the sand with no death wobble at all. Hit the pavement or gravel road and it comes back. I think the sand is slippery enough that it just can't get started whipping back and forth.