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Old 08-12-2014, 04:06 PM   #1
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Is this the death wobble?

Hi,

I've been out on the same road and twice now in two different directions and in two different places I have enjoyed/endured/survived a wild ride.

Details:

1- driver alone-once with dog- 1985 Advanced 4x4 leaf spring conversion- very short front end shock travel- +\- 3 inches
2- light load- 6800 lbs total GVW
3- 35- 40 mph
4- road not pot holed, but not very smooth either
5- I hit a series of 2 or 3 small bumps

Then BLEHHHCK! The van feels like I've dropped the driveshaft with a crazy vibration that threw the mutt off his perch to the floor. I feel no pull on the wheel. The van stops straight and normal. I park, crawl underneath expecting the chucked pole vault tool to be lying on the ground and nothing. All driveline parts feel tight. Wheels too.

I think the series of bumps is setting up a bad cyclic vibration that the shocks with their limited travel and perhaps old age are unable to control.

It feels like the left front end is going to fold over and land on the road.

Any thoughts appreciated.

Regards,

Gavin
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Old 08-12-2014, 04:09 PM   #2
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Re: Is this the death wobble?

Quote:
Originally Posted by Pntyrmvr
Hi,

I've been out on the same road and twice now in two different directions and in two different places I have enjoyed/endured/survived a wild ride.

Details:

1- driver alone-once with dog- 1985 Advanced 4x4 leaf spring conversion- very short front end shock travel- +\- 3 inches
2- light load- 6800 lbs total GVW
3- 35- 40 mph
4- road not pot holed, but not very smooth either
5- I hit a series of 2 or 3 small bumps

Then BLEHHHCK! The van feels like I've dropped the driveshaft with a crazy vibration that threw the mutt off his perch to the floor. I feel no pull on the wheel. The van stops straight and normal. I park, crawl underneath expecting the chucked pole vault tool to be lying on the ground and nothing. All driveline parts feel tight. Wheels too.

I think the series of bumps is setting up a bad cyclic vibration that the shocks with their limited travel and perhaps old age are unable to control.

It feels like the left front end is going to fold over and land on the road.

Any thoughts appreciated.

Regards,

Gavin
Yep, that's it.
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Old 08-12-2014, 08:13 PM   #3
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Re: Is this the death wobble?

Some light reading:

viewtopic.php?f=3&t=9967

http://www.sportsmobileforum.com/viewto ... 9&start=15

Basically install dual opposing gas pressurized shocks like TurboStew did (and I did on his recommendation) and if the symptoms go away, then it is death wobble.
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Old 08-12-2014, 10:47 PM   #4
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Re: Is this the death wobble?

I thought the death wobble was more associated with a coil setup rather than leaf springs?
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Old 08-13-2014, 07:38 AM   #5
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Re: Is this the death wobble?

Quote:
Originally Posted by JoeH
I thought the death wobble was more associated with a coil setup rather than leaf springs?
No truth to that.
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Old 08-13-2014, 08:05 AM   #6
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Re: Is this the death wobble?

Quote:
Originally Posted by Pntyrmvr
The van feels like I've dropped the driveshaft with a crazy vibration that threw the mutt off his perch to the floor. I feel no pull on the wheel. The van stops straight and normal.
If it were "Death Wobble" you would feel it in the steering wheel and I mean really feel it - even see it as the steering wheel shakes back and forth.

"Death Wobble" is when the tires/wheels and steering components move rapidly left to right, right to left, at an uncontrolled rapid rate.

It is steering movement through worn or weak steering or suspension components, initiated by either an uneven surface, out of balance tire/wheel, or impact with something.

The "Death Wobbles" are caused by the self-centering characteristics (Steering Inclination Angle and Caster) of the front suspension and component wear or weakness. When one front tire, say the Right Tire/Wheel, is deflected away from center by hitting a bump, rain groove, tire problem, alignment problem or whatever, it in turn drags through the steering components, the Left Tire/Wheel away from center also. Because there is wear and flex within the steering components (tie rods, tie rod ends, drag links, idler arms, etc.) and suspension components (I-beam bushings, Radius Arm bushings, Ball Joints, etc.) there is a delay between the initiating Right Tire/Wheel and the reacting Left Tire/Wheel. Then, because of self-centering, the Right Tire/Wheel tries to move back to center just before the Left Tire/Wheel tries to move back to center, which because of the above wear and flex, is also being forced back over by the Right Tire/Wheel through the steering components. What happens is that the Right Tire/Wheel and Left Tire/Wheel get out of phase with each other and start a resonance that compounds until both Tire/Wheels are fighting each other and they are oscillating wildly back and forth out of phase. This harmonics will generally only stop when something disrupts it like turning the steering wheel quickly one way, slowing down, slamming on the brakes or even by hitting another bump.

So, the reason that you get so many different recommended fixes for the problem (new I-beam Bushings, new tires, new shocks, re-alignment, etc.) is because that all of them individually or several combined can be the trigger for “DEATH WOBBLES”. My experience has been that incorrect caster and toe settings are the biggest culprit. By incorrect, I do not mean based on the factory settings; those are for stock setup. Once you have lifted or modified the suspension or changed the Tire/Wheels factory setting may not be optimal. New components, being tighter will help to solve the problem, but I have found that more caster is the best solution assuming all good parts. Adding more caster increases the self-centering characteristic and helps to keep the Tire/Wheel tracking true and less likely to deflect away from center. “That same effect is what makes the truck want to go straight down the road at speed b/c each front tire is trying to get to it's lowest (unloaded) position. The lowest position for the left front is at full right turn and vice versa. At some point (hopefully going straight) they reach a balance.”

Interestingly, on some vehicles, removing caster seems to help as well.

Quote:
Originally Posted by Pntyrmvr
I think the series of bumps is setting up a bad cyclic vibration that the shocks with their limited travel and perhaps old age are unable to control.

It feels like the left front end is going to fold over and land on the road.
All that said, I don't think you are describing "Death Wobbles" - it sounds more like suspension related as you noted.
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Old 08-13-2014, 09:11 AM   #7
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Re: Is this the death wobble?

Quote:
Originally Posted by BajaSportsmobile
Quote:
Originally Posted by Pntyrmvr
The van feels like I've dropped the driveshaft with a crazy vibration that threw the mutt off his perch to the floor. I feel no pull on the wheel. The van stops straight and normal.
Woops, missed that part. Yeah, steering wheel would be going side to side.

When I had it on my old van, it was a very simple (once you find it) issue. The track bar had wallowed out the upper mount that Quigley installs, probably because the bolt had come loose because it was installed the wrong direction and was hitting the axle. Allowed the track bar to move a tiny little bit. Had my guy fabricate a new stronger mount, install new bushings and the bolt correctly, and no problems.

Which reminds me, I should check that on my new van.
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Old 08-13-2014, 09:20 AM   #8
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Re: Is this the death wobble?

Quote:
Originally Posted by BajaSportsmobile
Quote:
Originally Posted by JoeH
I thought the death wobble was more associated with a coil setup rather than leaf springs?
No truth to that.
OK, but will you agree that this term is most frequently associated with a Quigley 4wd conversion?
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Old 08-13-2014, 09:23 AM   #9
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Re: Is this the death wobble?

Quote:
Originally Posted by rallypanam
Quote:
Originally Posted by BajaSportsmobile
Quote:
Originally Posted by Pntyrmvr
The van feels like I've dropped the driveshaft with a crazy vibration that threw the mutt off his perch to the floor. I feel no pull on the wheel. The van stops straight and normal.
Woops, missed that part. Yeah, steering wheel would be going side to side.

When I had it on my old van, it was a very simple (once you find it) issue. The track bar had wallowed out the upper mount that Quigley installs, probably because the bolt had come loose because it was installed the wrong direction and was hitting the axle. Allowed the track bar to move a tiny little bit. Had my guy fabricate a new stronger mount, install new bushings and the bolt correctly, and no problems.

Which reminds me, I should check that on my new van.
Good to see that you found the root cause. I've seen too many people slap a steering stabilizer (or two) on steering/DW issues and consider it fixed, while the underlying problem hasn't gone away, and will likey continue to degrade until a catostrophic failure results.


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Old 08-13-2014, 09:35 AM   #10
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Re: Is this the death wobble?

Quote:
Originally Posted by BroncoHauler
Good to see that you found the root cause. I've seen too many people slap a steering stabilizer (or two) on steering/DW issues and consider it fixed, while the underlying problem hasn't gone away, and will likey continue to degrade until a catostrophic failure results.


Herb
Completely agree. Like turning up the stereo when the motor's making noise, steering damper just masks the problem.
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