snap oversteer (1 Viewer)

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Is it possible that your panhard bar geometry tends to roll the top of the axle forward when you turn one way and backward when you turn the other way. The result being an increase in caster when turning direction A and a decrease in caster when turning direction B.

Ref: "The Caster angle is the ability of the front suspension system to self centre under cornering loads. Too much caster and the front of the car will understeer more (positive caster), too little and you will get oversteer handling characteristics (negative caster)."
 
I mean during the forces of driving. Lateral G's cause a push force in panhard which maybe pushes on the bracket on your axle. When turning the other way the pull force in panhard pulls on the bracket. You'd be able to judge by observing at what speeds and therefore lateral forces this occurs at maybe. Or put a go pro camera under there.
 
I get that feel if the shackles are a little loose, I would make a slight panard bar adjustment and see if it persists, maybe it is just the way your links feel and you get used to it . I do believe the drag link angle lends to the loose area you feel getting into the turn , I know the feeling
 
all in all, though, those are good thoughts for diagnosing the issue presented.

there isn't a shackle to be found on my '40. And at the moment everything is brand new. As for pushing brackets, the frame is pretty stout since I boxed it and fully welded it.... the lower arms all ride on a 2x4 1/4" wall cross member...
 
Well I hope when you figure it out you'll let us know the cause. I still say steering box.
 
Are the suspension links rod end or rubber filled joints? If spherical rod ends it kind of eliminates my suggestion of axle roll. I was thinking rubber like a stock 80 series has. They could move around quite a bit.
 
Last thought. With regard to your steering box pitman arm and steering arm at the king pin axis. Is it possible that the geometry of the pitman relative to the steering arm is causing a non-linear behavior? Hard for me to describe. But if your pitman is straight when your wheels are straight then it will have equal sideways movement in both directions when you turn the wheel. But if your steering arm was 45deg to one side when your wheels are straight (exaggeration for description) then it would behave nonlinearly. When you turned one way your wheels would turn more than your input. When you turned the other way your wheels would not turn as fast as the steering arm was brought towards straight ahead from 45 deg. You could measure everything up and model it in Solidworks to see the behavior although this would be a bit of work.
 
SuperBuickGuy said:
for the record, my first car was a 1962 Buick Skylark with bias ply tires on it, the FJ40 I owned in Reno (number 2) never had a radial tire on it.... point is, I've more than just a little experience with the quirks of bias ply tires.... this isn't a bias ply tire problem.
Click to expand...
How many cars with 38" swamper bias ply tires have you driven?
When you have eliminated all the possible solutions it's time to look at the impossible solutions.
Swampers are odd beast, try rotating the tires, just straight across, left to right.
 
rusty_tlc said:
How many cars with 38" swamper bias ply tires have you driven?
When you have eliminated all the possible solutions it's time to look at the impossible solutions.
Swampers are odd beast, try rotating the tires, just straight across, left to right.
Click to expand...

oh my goodness, you caught me, I've never driven a car with 38s on it. Of course, I've driven dozens of trucks with them on it. This is, however, the first 4 linked, extended wheelbase, FJ40 with a Chevy 350 and 5 speed that I've driven with 38.5s. You think that's relevant? oh wait, I did drive a buddy's FJ40 with 42s on it, but it was an automatic - so perhaps I should go find someone else with a similar '40 so I can be sure? schmidt man... really?

that said, it's a good idea to swap sides - I'll give it a shot.
 
SuperBuickGuy said:
oh my goodness, you caught me, I've never driven a car with 38s on it. Of course, I've driven dozens of trucks with them on it. This is, however, the first 4 linked, extended wheelbase, FJ40 with a Chevy 350 and 5 speed that I've driven with 38.5s. You think that's relevant? oh wait, I did drive a buddy's FJ40 with 42s on it, but it was an automatic - so perhaps I should go find someone else with a similar '40 so I can be sure? schmidt man... really?

that said, it's a good idea to swap sides - I'll give it a shot.
Click to expand...
This is when we need the eat a dick emoji on this site.
 
SuperBuickGuy said:
when sarcasm just isn't enough, emoji
Click to expand...
Since you appear to be completely fxxxing clueless;
When someone offers a helpful suggestion reply graciously.
Do not boast about how fxxxing great you are, and all the fxxxing wonderful things you have fxxxing done.
Nobody gives a fxxxing s***.
I am pretty fxxxing sure you were not running bias ply 38" swampers on your fxxxing Skylark, I have no fxxxing idea when you owned your fxxxing FJ40 in Reno and if 38" swampers were available at that time. Nor do I fxxxing care.
By the way I am totally fxxxing impressed that you drove a "friends" FJ40 that had 40's.
And nobody buys your fxxxing sarcasm s***, which you seem to trot out every time you fxxxing piss people off. You are a fxxxing pompous ass, work on changing that.

Think this before you hit the post button;
"How would I feel if somebody replied to my helpful suggestion this way?"

I hope you take this in the constructive manner in which it is intended.


Then go fxxx yourself.
 
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rusty_tlc said:
How many cars with 38" swamper bias ply tires have you driven?
When you have eliminated all the possible solutions it's time to look at the impossible solutions.
Swampers are odd beast, try rotating the tires, just straight across, left to right.
Click to expand...

since we're being all honest and crap - try reading your post without getting a condescending prick. All I did was repeat your words back to you "oh, swap your tires" and you blow up. The irony is it's your own words that irritated you.

Funny thing is, I wasn't dissing your response, the words I said I meant.... it was a good idea and I will try it...

seriously, grow some thicker skin.

Oh yeah, and also - I seriously thought against asking the question here. I asked it elsewhere and in 4 posts had 3 different ideas that have merit - all without drama. What I don't get is anywhere else, it's never a problem - but on 4x4 forums, it's like people are trying to pose to look smart....
 
Who narrowed that axle? Are you sure the caster is the same on both sides? Also what amount of caster is it set at?

Who built your link suspension?

IMO the cause of left/right difference is related to your suspension causing the distance between the steering box and passenger side tie rod end to change. As the body roll happens the change in that distance causes a steering change. Combine that with negative camber and toe out that both tend toward oversteer and it may be a few small things that add up to a problem. Especially if you're only in the low single digit caster range. I prefer to run around 6* caster on my FJ40, but it's also using the Toyota SAI, I don't know what SAI range Dana axles normally run at or how you'd then want to set your caster.
 
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