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HELP ! Death Wobble. Caster angle ?

blu3fan

NAXJA Forum User
Location
Arizona
Hello again guys. Im back with another question.


92 xj 4.0 242.

my 4-5 inch lifted cherokee had some slight wobbles.
I suspected it was due to caster angle.
Bought core 4x4 adjustable control arms.
and moog v8 grand cherokee steering rack.

Set it up and I am missing something here.

So. To ensure positive camber. I should have 4-6 degrees of positive camber is what im reading and hearing

Yet this seems impossible to achieve. the driveshaft at that point would be severely angled on the U joint of the axle itself. the amount of force needed to bend it that much seems impossible.



I set it to -4 degrees from where it was before. It drove badly.
set it at 0 today took it out for a drive. was fine until 45. then holy crap death wobbles.


help? how am I supposted to angle this ?
 
my main question is. how do I get the axle to bend that far backwards. I jack from the track bar to bend it backwards.
any other ways to do this ?
 
-what upper control arms do you have?
-what lift is in there (i know the height I want to know the lift or what pieces
-since its a 92 im assuming its a hp30 you have unless swapped with something else
-What track bar are you running
-What steering setup are you running
Their is a method to my madness here....then I will answer how you can achieve your desired caster numbers
 
I run 2.9* of caster on my 2000 with perfect control!
 
First, the t-case drop isn't doing your front driveline any favors. You're far better off with an SYE and no drop. I'd say you still need a bit more caster. Generally speaking having the top of the axle rolled back 5-8 degrees is the working area. Too much or too little will give you a case of the wabbles. Mine is really happy at about 6 with similar lift height on 33s.
 
First, the t-case drop isn't doing your front driveline any favors. You're far better off with an SYE and no drop. I'd say you still need a bit more caster. Generally speaking having the top of the axle rolled back 5-8 degrees is the working area. Too much or too little will give you a case of the wabbles. Mine is really happy at about 6 with similar lift height on 33s.


so.
Were at 4degrees positive caster angle now.
Im reading some things. and im just utterly lost here.
I am reading things telling me screw the caster angle and to just make sure the U joint in the front has 0Degrees pivot.
Doing this would put me back at -4/-6 degrees caster angle. *back where I was at. I could do 85 on the freeway here. with just a slight wiggle.


which is correct ?
 
At 4+ i Took it to 45mph. seemed okay. then at about 50 I felt a little shudder. slowed down and knew it wasnt fixed.
 
Okay. So I’ve done some reading.
The double Cardon joint needs 0-1degree input.
By adjusting my steering down. All I have done is shifted the weight from the outside of the tire to the inside.
Makes it better but not fixed.
Adjusting the axle shaft to be 0 degrees and just dealing with having negative castor is the best we can do without cutting the ears off
 
Beside the alignment issue, you have loose parts somewhere in the suspension or steering, or both, that's allowing the death wobble to occur.
It's time for a complete inspection.
Have you had someone sit in the driver's seat and rock the steering wheel back and forth while you get under the front end?
Look and use your fingers to feel for movement in bushings, ball joints and tie rod ends.
Track bars are especially prone to problems, tighten the track bar frame bracket and the rest of the front end hardware to FSM specs.
 
LazyXJ though you are correct that many times DW is caused by worn parts I can assure you that even with EVERYTHING brand new you can get death wobble simply from having the caster out of whack. When I first got our shop comanche I replaced every piece of the front steering and suspension system with new. Every single wear part down to the shocks, bearings, ball joints, control arms, brakes, and steering. Caster was at 9 degrees and hitting an expansion joint would send it into such violent death wobble the freaking ashtray fell out and the glove box opened. This was stock height with stock tires. I rolled the axle forward to 6 degrees and it's smooth as glass driving 80 with one finger on the wheel.

As for the OP, you're getting confused with 2 different things. Pinion angle and caster. They are connected because it's a solid axle, but because it's your steering axle you have to compromise on one or the other. You can't have both perfect without cutting the knuckles off and rotating them. Since you seem to want the thing to drive properly you're going to need to forget about the pinion angle for the time being. Also stop using positive and negative terms, because I'm betting nobody is following you. As I said before you want the top of the axle rotated BACK, which means pinion down. Call that positive or negative or whatever I don't really care, but having it rolled forward is a big no no. You want the contact patch of the tire to trail behind the line that is projected through the upper and lower ball joints. This is what makes the steering want to return to center. You need enough caster for it to want to go straight, but not so much that it snaps to straight and starts shaking like mine used to do. Too much or too little are both bad. Here's a diagram that might help, it's showing a strut suspension, but the concept is the same.
caster-diagram1.jpg
 
In a perfect world you'd have the pinion in line with the driveshaft, and the proper amount of caster. In this case you can't have both (not easily anyways) so you deal with a less than optimal pinion angle so that it'll drive without being a safety hazard.
 
5" on factory mounts/arms isn't helping either. You should consider DB's.
 
If all the suspension and steering parts are quality brand name parts, as suggested, control arm drop brackets will be an improvement to both the suspension geometry, and the ride quality. If any of the suspension/steering parts are not in best condition, they probably should be replaced.

Did you list all the modifications, and their brand name/type ? Have you checked the axle end track bar mounting bolt for an ovaled out bolt hole ?

Nearly everyone, balances the pinion angle against the caster. Just enough pinion angle to reduce or prevent vibrations, and just enough caster at the same time. Neither one will be perfect, but both will probably be close enough.
 
Just a recap from a guy that has dealt with helping dozens of guys cure DW over the last 20 years, DW is normally caused by a cluster of issues, rarely only one.

Fixing one issue, may or may not "cure" DW. DW is basically an instability in the steering system allowing it to oscillate. Historically I have seen almost all cases to be related to mounting points or joints that have looseness or play, allowing things to shift back and forth.

Surprisingly enough, holes in brackets that have been worn into oblong instead of tight fitting holes have been a common culprit. The key is to find out where there is ANY play in any mounting or joint. Castor just makes this worse.

Without cutting the knuckles loose from the axle, rotating them, and re-welding them, castor vs pinion angle is always going to be a trade off.

It only takes a few minutes to find the looseness, but it takes two people. Just grabbing a joint and trying to wiggle it does not work. You have to have one person inside, rocking the steering back and forth while you observe each and every attachment and joint for movement. Once the looseness is found and fixed, find a happy medium on the pinion angle/castor and give it a shot.

Steering dampers do not cure DW, they only mask it and tend to be a short term fix at best.
 
Nothing is loose.
As someone stated before. When this type of dw happens with castor.
The front axle danm near fell off.
This is due to the u joint angle
So. If I’m at +4 I wanna aim for +6/+8?

It seems counter intutitive
 
As old_man correctly stated, DW is almost always a combination of worn/loose/damaged steering and/or suspension components. Very rarely is one single item the cause, or the cure. Caster issues may or may not trigger the DW, but it not the root cause of DW.

I am done here ….
 
As old_man correctly stated, DW is almost always a combination of worn/loose/damaged steering and/or suspension components. Very rarely is one single item the cause, or the cure. Caster issues may or may not trigger the DW, but it not the root cause of DW.

I am done here ….


Okay. I understand your point.. but.
Let me give you a little background here.
This all started when I lifted it with the stock control arms.
It had a Tiny Tiny wobble at about 70. not drive effecting at all.
I knew my ball joints and other things on the front needed being done. So I figured why not. just do it all.

In the last month.
I have replaced.
Hub Bearings. Both sides. Timken.
Axle shaft u joints. Both sides Dana.
Control arms. core 4x4 upper and lower.
Upgraded steering rack to v8 grand cherokee rack. Moog.
Both upper and lower ball joints Both sides. Dana.
Upgraded to fancy axleshaft seals. the billet aluminum ones.


Three days ago. I adjusted my caster from the -4 it was at. where the Driveshaft pinion was almost straight to the xfer case.
but I had read this was bad. due to the axle having nowhere to "rest on"
Drove it up the street and the thing at about 45 after showing no vibes til that point... Pretty much she tried to eat the front axle.
I suspect that adjusting the pinion angle to 0 degrees caused the turning forces to bind the u joint in the driveshaft at that speed.


Now. with the axle at +4 degrees. The springs are literally ) <--- thats what they are doing.
the driveshaft is looking to be at quite the angle to the xfer case.


.
I understand the problem that without adjusting position of the C ears on the end of the axles I cannot get an ideal situation.
how much angle can I get on that front driveshaft U joint before its gonna bind at speed ?
 
*** Currently at +4 caster It drives to 45mph. Im too scared to go further until I confirm this after it almost totaled itself on the test drive At 0Degrees



Anyone who says caster angle cannot cause death wobble. Doesnt know what death wobble is yet.... trust me you don't want to know.



There was a comment about the ashtray coming out. Not surprised. it was that bad.

When mine shook at 0 Degrees my rearview mirror clip on. came off.. that thing holds on tight.



Been driving this car and working on it for 12 years.
This is something beyond death wobble. maybe it should have its own name... LOL !!!
 
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