definitive cause of death wobble

[ihscoutsniper]

I recently purchased and retrieved my A3, I had kenny pick it up from Mccoy and bring it to his shop. He sent a video of the deathwobble, we test drove it and found the same problem.
After some inspection, everything looked ok in the front end except that the passenger steer tire had an odd scalloping to the tread, so we switched it out with the spare which was new. This seems to have helped a little, and on the 9 1/2 hr trek home it never reoccured.
the next day however it was back and often pops up at mid range speeds, you can seemingly power through it and it smooths back out around 45 .
i have been trying different air press. as this does seem to have some effect.
Does anyone know a definite cause and repair to eliminate this problem as it seems to be (in my opinion) the only flaw in the A3?

 

[Bob H]

It will only get worse.
In my experience death wobble isn't usually just one part, it is the sum of the worn parts, i.e. bearings, kin pins, tie rod ends, steering linkages and yes the tires. An issue with A3's is the tires, if they sit flat for a long while, like waiting to come up for auction for 2 years, the sidewalls are seriously compromised and unsafe. Always put your best tires up front. To inspect the tires properly, inside and out, they need to be dismounted.

 

[gringeltaube]

.... And don't forget tire/wheel balancing! I would put that on top of the list...

G.

 

[Z71]

Is balancing singles required by the Army TO? No such requirement exists for M35 equipped with 9X20 NDT tires.

 

[ihscoutsniper]

I had a theory going in my head, it may not be the cause but I think it accentuates the problem.
Firstly has anyone seen or heard of anyone putting the bigger tires on an A2 and then getting death wobble?
If not we have to look at the primary difference in the front ends, which would be the air assist for the steering. Seeing how this is accuated leads me to believe that a little bump steer could start the system fighting itself in a back and forth reaction, leading to the heavily pronounced death wobble.
Now this is not to say the front end parts aren't in need of attention, just that I can see where this would really cause an uncontrollable wobble..
I am considering disconnecting this system for a test drive and seeing what happens.
Any thoughts?

 

[nk14zp]

Sounds like a great idea.

 

[gringeltaube]

Is balancing singles required by the Army TO? No such requirement exists for M35 equipped with 9X20 NDT tires.

Well, don't know, prob. not...
But who cares; we already learned that keeping front wheels & tires (yes even brake drums!) well balanced makes a huge difference for everything going over 25mph. Unbalanced front tires, be it super-singles or not, will cause anything ranging from slight shimmy to the most fierce death wobble!

See this thread: http://www.steelsoldiers.com/deuce/32924-14-5-xl-rear-tire-harmonics.html

G.

 

[monkster]

Bob H is right it is the some of the whole. I have had this with 10 wheeler grain trucks. Put new king pins in replaced tie rods only to find we had a bent axle. Now granted this is nt a 6X6 trk but it made the caster and camber wrong.

 

[hoop]

Front end alignment.

 

[cranetruck]

Match the front tires by wear, date code and manufacturer, that has been my cure over the years, even with a good front end alignment and new shocks.

 

[renovate7]

How many miles on the truck? If it's not many I doubt steering components are worn out. My A3, like all the others, had a very noticible shimmy around 40 mph. I aired the tires to 52 psi and added 1.2 lbs of lead shims on each wheel opposite the CTIS system. . Others add 3 full size lug nuts to do the same thing. This made my ride very smooth. If you have a bad tire that will certainly contribut a lot to it. Put your 2 best tires on the front, no matter what else you do. Also make sure the treads are pointed in the right direction. If one is pointed to the front and one to the rear this may cause issues...Not sure if your problem is like a DEATH WOBBLE I had in a 50 Chevy years ago. At 45 the car would occasionally shake so violently you thought the whole front end was coming out of it. Scared the bejeebers out of the passengers. Turned out to be BAD kingpins.

 

[tigger]

In the semi's it is usually kingpins or spring shackles!

 

[paulfarber]

The best tire advice I have:

All tires on an axle should be within 1/4inch diameter. Properly inflated (50PSI for hard surface roads) and must have a shraeder valve cap!!!!!

Tire balance is not an issue until you hit 50+MPH. Below that its not a concern.

My 42 jeep and 43 CCKW have repair steps to adjust the steering gear. There are only three moving wear parts: kingpins, tie rods and the pitman arm and drag link.

On a jeep rebuild the first thing you do is throw away those parts and buy/rebuild them.

 

[ODdave]

There are only three moving wear parts: kingpins, tie rods and the pitman arm and drag link.

Might wanna re-word that.

 

[jeep454x4]

And that is why I love my M35A2 takes a lickin and keeps on tickin no wobble probble here

 

[AMX]

And that is why I love my M35A2 takes a lickin and keeps on tickin no wobble probble here

The A2 also doesnt have a 382lb. wheel/tire assembly.

 

[ODdave]

The A2 also doesnt have a 382lb. wheel/tire assembly.

mine dose......

 

[gringeltaube]

It may not be that heavy but yes, much more than a stock 20x7.5"wheel + 9.00-20 tire which comes close to 220lb.
In addition to it, if you decided to retrofit an A2 with 14.5 tires/11"wide wheels you better do balance them, before. Even if you are not planning to go faster than 45mph....

G.

 

[ODdave]

G, how are you guys balancing them? with a spin balancer or a static/bubble type? I ask because shops around here wont touch a tire this size

 

[paulfarber]

Might wanna re-word that.

No, those are the correct parts. I am talking about the steering part. You *could* add the steering box, but unless its been run dry or defective its not a *WEAR* part.

The axle has rotating part, but we are talking about steering components.. and those are the only steering components on the truck.

Springs do not steer the truck, they are there to absorb road loads transmitted to the truck via the tire.