Death Wobble, cannot track it down

[Tools R Us]

... All that being said, I don't think caster is the cause of your death wobble.

Agree, most times neutral caster is the most "shake proof", excessive caster for the setup (positive or negative) tends to be more shake prone.

CV front shaft?? you mean DC???

The answer to that is no, but that only causes drive line vibes, which I have. Barely noticable though.

Agree, drive shaft vibe has nothing to do with death wobble.

Death wobble can be frustrating/elusive to figure out. The things that I have seen cause it:

Tires, especially tall/heavy tires that have sidewall area balance issues. This causes the tire to oscillate (turn) back and forth. Can be difficult to find on some balance machines, especially with tall/heavy tires and with them it can be difficult to 100% rectify.

Anything that will allow the frame to have side to side play over the axle. In the '80 case, the panhard is the most common offender. The taller the lift, the more leverage the frame carried mass has over the axle, bushings, etc, added weight only makes it worse.

Excessive caster for the setup can cause it, will make it more shake prone.

Excessive play in wheel, knuckle, bearings can cause it, but mostly falls with the next group.

Steering box, tie rod ends, etc, on a proper setup they can have an amassing amount of play and not cause death wobble. Death wobble is very violent, puts huge loads on components, so most often play in these parts is the result of the beating, not the cause of the problem.

Steering stabilizer, a properly setup rig should run fine without it. It's job is to reduce kick back in the steering wheel, so is for operator comfort. They can mask the issue, but if there is an issue, it is best to find/repair it.

Unfortunately, death wobble is one of those things that is almost impossible to diagnose over the web, need to see, feel, etc, to get a handle on it.

 

[Ebag333]

Caster is determined by the angle of the steering axis in relation to the road. Frame angle can affect caster angle.

The higher you raise the back, the more you point the front at the ground. Caster is essentially how far up or down the front axle is pointed.

I see what you're saying, but you're still not going to make that large of a difference unless you have something silly, like 5" of stinkbug.

Raising the back does pivot the front around the spring perches (close enough to the axle for our purposes), and since the front arms mount behind the axle it will lift it up some. But because it's pivoting, and because the front arms are far closer to the front axle than the rear, an inch or two of stinkbug won't make a significant difference in the height of the frame side of the control arm mount.


Regardless, his caster is above 0*. I've seen (and driven) plenty of trucks with negative caster, and no death wobble. If he was running -3* caster, yeah, I'd say that could be a factor, but being positive? Unlikely that's the culprit.

 

[rove_mcanus]

Have you checked your wheel bearings and/or kingpin?

x2. Most people don't do these up tight enough.

For a wobble to occur that is so violent you have to slow down/stop there must be something loose or worn in the front end creating enough free movement for momentum to build.

Tyre imbalance and alignment is only the catalyst to the death wobble.

Since your castor is .6 degrees, then you must either have more then 6 inches (close to 7), or you have the wrong slee arms (or the slee arms were made wrong). To measure lift you must go off the distance between the metal spring perch, and the rubber/plastic bump stop (toyota call it a spring follower) inside the coil. Standard spec is something like 1 inch, but you should find out exactly what.

Also at this height you should really consider drop boxes.

 

[rove_mcanus]

Just another thought, you say you have new oem (rubber) bushes. It's possible with the angle of the radius arms, added weight of rims/bigger tyres and the increase of force from bumps at highway speeds, you are actually getting movement in the rubber of the bushes. You could try some firm poly bushes instead.

 

[sleeoffroad]

I actually sent him a PM after I saw my numbers.

There shouldn't be a need for plates, or bushings though. The Slee arms are designed to put the caster back into operating range with the Slee 6" lift kit.

Hopefully he will post up and hopefully all I need is plates or bushings to remedy this, although I don't know why I would,.

Do you have 6" of lift or more? The caster is not ideal but it is not that bad either. I highly doubt that it is the cause of your death wobble.

The initial arms we made for a 5" lift when we used J springs with spacers, then we went to 6". Do you know when these were sold? Are you original owner?

There is a possibility of using caster bushings with the arms, just not at full adjustment. One has to make sure that the notch in the arms are not going to touch the axle housing when rotated.

When we ran UA with the shortbus, it had terrible death wobble. It was set up correctly in caster but it had hydro steering. We could not solve it and ran out of time before the event to trouble shoot it. We ended up running the road sections of the event with the front suspension sucked down onto the bump stops. We later figured out it was related to how the body swayed and upsetting the frame. This in turn caused the panhard (both front and rear) pulling on the axles and changing he steering and it then went into a harmonic that just amplified to a point where you could not control it.

I would try to lower the truck and see if you still have it. I would also try to get the back down and see if that changes. With the rear end high, the panhard is at a pretty good angle. Any body movement is going to make the rear axle steer and you might be compensating for that up front and starting the wobble.

 

[sleeoffroad]

but I don't, with a heavy ass bumper and winch it causes the springs to compress more and you don't have 6" anymore, the 1" spacer doesn't even add an inch to it....

How is this possible, unless the spacer is compressing.

 

[lt1fire]

How is this possible, unless the spacer is compressing.

I don't know about this but I measured the same points before and after the installation and got about 1/4 of lift.

 

[lt1fire]

Do you have 6" of lift or more? The caster is not ideal but it is not that bad either. I highly doubt that it is the cause of your death wobble.

The initial arms we made for a 5" lift when we used J springs with spacers, then we went to 6". Do you know when these were sold? Are you original owner?

There is a possibility of using caster bushings with the arms, just not at full adjustment. One has to make sure that the notch in the arms are not going to touch the axle housing when rotated.

When we ran UA with the shortbus, it had terrible death wobble. It was set up correctly in caster but it had hydro steering. We could not solve it and ran out of time before the event to trouble shoot it. We ended up running the road sections of the event with the front suspension sucked down onto the bump stops. We later figured out it was related to how the body swayed and upsetting the frame. This in turn caused the panhard (both front and rear) pulling on the axles and changing he steering and it then went into a harmonic that just amplified to a point where you could not control it.

I would try to lower the truck and see if you still have it. I would also try to get the back down and see if that changes. With the rear end high, the panhard is at a pretty good angle. Any body movement is going to make the rear axle steer and you might be compensating for that up front and starting the wobble.

No but somewhere I have the original invoice from you, i'm 99% sure it was your 6inch and not the old OME 5" you first started selling.

When you say body sway are you saying that the body to frame mounts might be bad or need to be replaced.

 

[sleeoffroad]

No but somewhere I have the original invoice from you, i'm 99% sure it was your 6inch and not the old OME 5" you first started selling.

When you say body sway are you saying that the body to frame mounts might be bad or need to be replaced.

No, complete body with frame moves.

 

[sleeoffroad]

I don't know about this but I measured the same points before and after the installation and got about 1/4 of lift.

I doubt that 1" spacer will compress to 1/4". The only other thing might be that the shocks are completely topped (extended) out and keeping the lift at the height you measured.

 

[lt1fire]

I doubt that 1" spacer will compress to 1/4". The only other thing might be that the shocks are completely topped (extended) out and keeping the lift at the height you measured.

well i'm not going to debate this, I will submit to the fact that I might have measured wrong. :whoops:

i'll load up the rear of the truck and see how that does it but i've been fully loaded before and still got it.

I'll also replace the axle housing in December after the last ride of the season and replace all the barings in the process.

I'll report back after that.

 

[Ebag333]

The only other thing might be that the shocks are completely topped (extended) out and keeping the lift at the height you measured.

Interesting thought.

lt1fire, what shocks are you running? If you measure the length of the shock when neutral (flat ground), what does that read?

 

[lt1fire]

Interesting thought.

lt1fire, what shocks are you running? If you measure the length of the shock when neutral (flat ground), what does that read?

Shocks aren't maxed out can't remember the specs off hand though.

 

[krzyabncanuck]

Al, Call me, just dealt with this on a cruiser at my shop. It was a 40 series but my way of checking for what it was should work for you to.

 

[Dave 2000]

And what was the reading on the spring gauge when you check the knuckles as per post #15? If we can ensure the basics are right then it is another doubt removed.

regards

Dave

 

[lt1fire]

Within spec per FSM

 

[lt1fire]

Al, Call me, just dealt with this on a cruiser at my shop. It was a 40 series but my way of checking for what it was should work for you to.

Darin shoot me a PM, my days are kinda hectic with work right now.

 

[semlin]

lie down under the front and systematically look at all the steering joints, the knuckle housing and the control arms while someone turns the wheel from lock to lock and then half turn to half turn rapidly. something may announce itself to you.

 

[Ebag333]

I was just reading through LT's front axle troubleshooting thread. Have you walked through his troubleshooting steps recently? I'm sure you've done it all before, but I'm guessing things have been changed/tried since then....

 

[weigellj]

All I can add is my grocery getter gets the death wobble at 35-40 MPH. Very violent

I have the slee 4" lift springs and the mr gasket rubber/poly spacer.

new MTR kevlar 35" tires that are balanced
New OME stabilizer.
New everything in the front, nothing is bent or moves or has play.

I believe it is the caster that is off and causing this on mine, and possibly yours.

On all of the rigs I have ever drove or seen with the death wobble, the main issue was the caster.

FJ40's and 60's, the fix seemed to be the cut and turn and most that had the wobble, it was completely gone

I am going to dig into mine tonight and see what my caster is at with my degree wheel.

Sorry I cannot ad more to the solution of your problem.