I have rebuilt my entire front end, 3" drop axle with 6 deg shims for caster, reverse eye mono-leafs, all new bushings, new tie-rod, and tie rod ends adjusted with 1/4" tow in and still get death wobble occasionally when I hit some bumps or potholes. Any ideas on what may be the culprit and how to resolve this issue?

 

Something went wrong in your design. Long " weak" springs exacerbate the problem. Maybe a bit much caster. How much slop in the steering box at center position? A panhard bar will correct it.

 

Springs aren't weak, extremely stiff, too stiff. Steering box is fairly tight without much slop. I have noticed that lower tire pressure increases the wobble occurring. Currently running bias ply @ 22psi.

 

These are the specs I use-
caster 3 degrees min...4 degrees max, max variation between wheels 1/2 degree.....camber 1/4 degree min 1 degree max, max variation between wheels 1/4 degree....toe in, in inches 0 to 1/16 max....king pin inclination 4 degrees + or - 1/2 degree, the specs are the same for the 250 also
6 degrees caster is kind of on the high side
I use an 1/8" toe instead of 1/4"

Raise your tire pressure to 30PSI

 

Any lateral movement (side to side)? If so a panhard bar MAY help. You may want to recheck your bolts and such on the front end to double check that they are all tight.

Good Luck,
Paul

 

I totally agree, also a steering damper may help.

 

Absolutely agree. If everything else checks out then a steering stabilizer is the way to go. It makes a big difference when installed on 4x4s particularly with larger than normal tires.

 

X3 on the steering stabilizer

 

I disagree on the steering damper. All they really do is hide the problem.

I'd try fiddling around with the toe adjustment. You mentioned that you set it at 1/8 instead of 1/4. Try setting it back at 1/4 or even a little more and see what happens.
If nothing else its easy enough to set/reset and it won't cost you anything

Good luck
Bobby

 

The tighter the toe the more stability you'll get. 1/8 toe is ideal with independant suspension, but with a straight axle 1/4 is desired. Toe at those measurement's will never cause a wobble, it will cause wandering if anything (neg toe will really cause a wander) A steering damper does just what is say's, it dampens the harsh jarring incured with a straight axle with large tires ( older 4 wh dr trucks ) Running this combo with bias ply tires is even worst.
Loose parts and Caster angles are what you have look at first

 

I agree the steering stabilizer should be a last resort thing. Better to find the real problem and fix it right. I noticed you said you had 6 degree caster shims, but you didn't say what your actual caster measurement is. Have you ever had the truck aligned at a shop with the proper gauges and equipment? I would be good to know where your settings truly are. With your chassis and suspension mods, you could be way off. And 22 pounds of air in the tires is basically flat. The specs in the shop manual recommend 36 psi with the 6.00/6.50x16 tires. 30-32 would probably be sufficient and give you a better ride. That's my 2c.

 

I agree the steering stab is just a band aid to hide the wound. I would look hard at the bias ply tires. There's a reason why they are obsolete. The belts often slip which causes a squirm. That squirm can easily turn into a death wobble. They also tramline, i.e. follow the seams and cracks in the road. Do you know anyone who you can borrow a set of radials from that will fit your truck for testing? Too much caster can exacerbate the issue, as can too low air pressure. Ever see a solid front axle dragster with a lot of caster come to a stop after a burnout? Talk about death wobble...
Final place I'd look at is at the wear and free play in the steering box. Lock the pitman arm with two C clamps on the frame so it can't move. Mark the steering wheel with a piece of tape, and measure how far it moves from one side to another. More than 3/4" can also produce death wobble and tramlining.

 

I concur that everything else should be checked first, but I have seen many vehicles that had this condition where everything was correct and to spec and verified several times and it still had the problem just as Schmitty describes. Also note that he says that it gets better with the tire pressure lowered to 22 psi.

A tire with a slipped belt will be felt worse at low speeds. You should readily notice this Schmitty.

Steering stabilizers are not obsolete, in fact just the opposite. You will find them as OE on most true off-road or performance models with big tires.

By all means check everything or have it checked on calibrated equipment but when everything is set correctly and if you find that you still have the problem, don't frustrate yourself.

 

I know it doesn't sound right but the toe adjustment can and will effect the death wobble. The drag link on my 49 was bent down. One day while working on the truck I took my floor jack out there and "jacked" it back into shape. Since the drag link is behind the axle when I jacked in back into place it increased the overall toe-in adjustment. The next time I drove the truck I had death wobble. I never had it before messing with the drag link. Several weeks had gone by and I didn't immediately recognize what I had done.
I checked the front end for slop and ordered up all new spring bushings, tie rod ends, etc. After replacing everything I still had death wobble. I went back and remeasured and reset the toe. For the life of me I can't remember if I added a bit more toe or decreased the amount of toe but it cured the death wobble.
I've had the truck on the road now for several years, Tire wear is good, there is no feathering of the tread and no death wobble.
Again, its an easy thing to check and adjust. If it doesn't cure or help the death wobble you aren't out anything but an hours labor and a frosty beverage or two.

I agree on getting rid of the bias ply tires....thats one change you'll never regret. Yes, there is a place for a steering damper, but in this case it would be just a mask to hide the real problem.

Good luck
Bobby

 

lowering air pressure improving the wobble can definitely be linked to bias belted tires. Having worked at a service station during the switch from bias ply to belted bias ply to radials and driving vehicles with each, I had a lot experience with the ideosyncrosities of each of them.
Lowering the pressure allows the belts to apply less contact with the road, the center of the tread recedes or "humps up" away from the road where it will have less affect.

The stabilizers are used with large tires because of the effect of the added unsprung weight, the leverage of the large diameter tire and the gyroscopic progression of all that large spinning mass overpowers the OEM steering damping. Try driving one of the SUVs with "dubs" on it, you can barely turn it.