Right, which is why I am still confused why forum users here are saying that the solution is to increase positive caster (no such thing as negative caster on these trucks).

Jim

 

For sure, maybe this will help.

Negative castor is what you find on shopping carts at Walmart etc.

As you can see in the pic, caster either positive or negative to much all equals DW, even if everything else is right




I can solve DW and trust me it was a hard learning process. I got DW, so I stopped in a shop, they said do this, another one said do that, others said just adjust the caster and it went on and on. Sometimes the suggestion helped but mostly it go worse, so bad in fact I could not longer drive it, any speed over about 5 mph and DW just exploded.

So I crawled under my rig and I laid there looking at my suspension, not sure how many hours and how man sketches on paper I made, but my goal was not just to understand how my suspension worked, but how it interacted with each component. Then after a lot of experimentation I began to understand why and with that came how to fix.

 

 

Just to clear this up. Shopping carts have zero caster but they have "trail". Trail is the distance between where the steering axis intersects the ground and the tire's contact patch. The shopping cart's steering axis (caster pivot) is vertical, but the axle is offset from the steering axis which puts the contact patch of the tire behind the pivot (steering axis).

It is the stabilizing force resulting from "trail" that counters the oscillation that is DW. DW occurs when the force of the oscillation becomes greater than the stabilizing force of "trail".

Ever see a shopping cart that has one front caster that wobbles crazily when you push the cart? That's the exact same thing as DW.

 

This subject is very interesting. Now for another question, What is different about the F 450 other than the wider axle. Its not talked about in the TSB ?

 

I do not know enough about the 450 to address as I have never owned one. I am sure theyu get DW just like any other vehicle can. You do not have to have a front driving axle to get DW, any car can can get it. The only times I have seen it on a passenger car it was due to worn bushings + low air in the tire(s). Worn bushing was in the lower A arm at the front and the tire was low on air.

 

Yes and no: IF you are OEM and DW occurs, my first advice is alignment and tire rotate, balance and door jam air pressure, if that does not cure it then it's something else besides caster, wheels/tires etc.

In my previous post it was caster that caused DW and in this case it was too much.

That said any component can play a part DW but some are more active than others such as the Track bar, Steering stabilizer and alignment/tires/wheels.

 

I have cured death wobble on many a vehicle especially jeeps. Used to build custom suspensions, not bolt on... from scratch builds

worn track bar, worn tie rods, having the vehicle (toe in) too high, too little caster can all cause death wobble. the system must work in harmony

death wobble on a brand new truck would be odd but it is possible
on a brand new truck i would look at toe and caster first.

to answer a previous question, the OEM sets the caster at the ragged edge of just enough because it makes the vehicle turn easier, more caster will make a heavier steering feel , the return to center will be a bit lazier and it will increase the turning radius of the vehicle. we used to build massive jeeps with 7 degrees of caster, they did not have the turning radius of a stock caster jeep, but you could take you hand off the wheel at any speed without fear of any movement.

my 2000 f250 7.3 and my 2005 excursion v10 were both set at 5 degrees of caster, guaranteed they took the road straighter than most other fords, I have not had my 2010 f350 for more than a couple months but i can feel a few things up front that i do not like. Ill go through it this next month or so.