Death Wobble - Possible Resolution

[sidetrak06]

Originally Posted by rallypanam

Sorry for the interruption to a great discussion... But this just showed up on my faceblog feed and I immediately thought of his thread:

I can't believe you waited until now to share this. This is obviously the CORRECT radius arm setup for minimum binding!

[sidetrak06]

In regards to my previous response, I will say that having the arms angled definitely stresses the poly bushings more than a parallel setup, which I could see leading to premature failure = movement. This could have an effect on my axle movement.

Please post if you see the geometry of this situation differently than I do. Maybe I am looking at this in the wrong way...

[arctictraveller]

Originally Posted by rallypanam

Sorry for the interruption to a great discussion... But this just showed up on my faceblog feed and I immediately thought of his thread:

[carringb]

Originally Posted by REF

out of curiosity, would it be possible to replace the radius arms with torque arms, like the adj. ones from CCV? would that set up be better?

CCV makes their own radius arm brackets for the '05+ axles and stock radius arms, which appear to have the proper offset to maintain parallel arms.

[sidetrak06]

Originally Posted by carringb

CCV makes their own radius arm brackets for the '05+ axles and stock radius arms, which appear to have the proper offset to maintain parallel arms.

I wonder if I could just use Derek's brackets since the ones on my van are a factory Ford item. I bet my radius arm would be compatible with it. I would have to move the bracket back slightly to compensate for the increased length once it is straightened.

[BajaSportsmobile]

Originally Posted by sidetrak06

This sounds terrifying, I think I will pass on the dynamic test, but I could try the static test if I get some nice ratchet straps.

I can't think of any reason it would be terrifying or cause any problem.

I also think the nonparallel radius arms are not the problem.

[shenrie]

Originally Posted by mgmetalworks

I know this is crude but I only had a few minutes...

crude is chicken scratch on paper with some sort of writing device. your sketch is wonderful for us that have a hard time visualizing. ty

Originally Posted by rallypanam

Sorry for the interruption to a great discussion... But this just showed up on my faceblog feed and I immediately thought of his thread

seems legit...

quick question somewhat pertaining to this thread. theres mention of steering stabilizer shocks in most every thread concerning dw. some say opposing shocks, some have a single. hear positive about both. i personally have a single rancho that im sure needs replaced. regardless, is there any negative effects on the power steering pump using these? seems like your creating resistance against your pump each time you provide steering imput.

im really enjoying this thread. thanks to all who are contributing!

[sidetrak06]

Originally Posted by shenrie

quick question somewhat pertaining to this thread. theres mention of steering stabilizer shocks in most every thread concerning dw. some say opposing shocks, some have a single. hear positive about both. i personally have a single rancho that im sure needs replaced. regardless, is there any negative effects on the power steering pump using these? seems like your creating resistance against your pump each time you provide steering imput.

im really enjoying this thread. thanks to all who are contributing!

I am not an expert on power steering but I will give your question a stab. Unlike your A/C compressor, which has a clutch and can disconnect itself from the drive belt, the power steering pump is always turning. It builds higher and higher pressure and volume as engine RPM's rise and there is an internal bleed off (check ball) if the pressure is too great so that it can continue to spin (pump) without destroying itself or other components.

The steering gearbox in a sense is a hydraulic proportioning valve. Turning the steering wheel does directly turn the tires, but it also controls a valve that directs the pressurized fluid from the power steering pump to one side or the other of a piston that assists with the turning motion. This valve reacts to changes in direction as opposed to a constant direction, which is good so that you don't turn the wheel and it keeps forcing you to turn tighter and tighter until you crash.

Regarding your question about steering stabilizers, yes it will put more resistance on the steering system that must be overcome. However, the job of the stabilizer is to resist sudden changes (bump in the road) but allow smooth changes (steering input). Just like a syringe, you can put very little force on the end and slowly empty the syringe. Or you can push very hard and it will empty only slightly faster. I don't know enough about the system to be able to tell you if the power steering pump and gearbox react to the additional resistance of a stabilizer and increase their operating pressure. I can promise you though that the damage in one bout with death wobble is much greater on your steering system than anything else and if that means you need to replace a $45 power steering pump a year earlier...count me in.

[E350]

This happens with all DW threads. The proverbial some of us are feeling the elephant's legs others the tail others the snout and all coming up with different conclusions.

carringb is smarter and more experienced than I am so I am reluctant to disagree with what he said about the trapezoid effect. I had the same question raised by sidetrak06 who, good on him, has the tenacity and the curiousity and adventurous spirit not only to want to build a rig like that (I probably would go with Baja's the long track Dana 50 if I could do it over again) and the tenacity to rework his design until he gets it right.

But for those of you who remain interested let's peel this onion a little further.

1. Some of you are thinking statically.

For you, stiffening up the frame, rejiggering the geometry of the frame, or buying a majic snake oil track bar is what you will spend your money on thinking that it will cure the DW. But in my opinion it won't.

2. A very few of you are thinking dynamically.

And it is always a minority who are thinking dynamically.

Bear with me here. My original hypothesis was half-assed and half-way in between static and dynamic thinking. For those of you who can follow my thinking that it was the "punch and rebound of an air-filled rubber tire" which caused the back and forth steering (wobble) transmitted through the tie rod, this always bothered me about my hypothesis: "Alrighty then! But why can't I cause DW with the vehicle stopped?" E.g., punch the tire sideways and see the other tire punch back and set up the DW reaction? Obviously movement is required, but if we put the vehicle on a flatbed (I actually visualized this in my analysis - this is how elemental my pitiful mind is) regardless of the flatbed's speed, the DW would likely not occur on the van on the flatbed. So the missing force in my hypothesis must be rotation not movement.

That's where Bajasportsmobiles's spinning gyroscope and bcaine's angular momentum stuff comes in. Just like a spinning top wants to stay spinning around its vertical axis, a spinnng tire must want to spin around its horizontal axis. Push a spinning top off-center (i.e., off the axis of its spin) and it immediately bounces back to its vertical axis. So that's what must be happening with the wheels in DW. Anything can push the spinning wheel off of its horizontal axis. A bump in the road, the other tire punching the wheel through the tie rod, etc.

Now here's where some static stuff comes in. A flexing frame or suspension can also likely cause a spinning tire to come off the axis of its spin. The bigger the ball joints, the bigger the hubs, the stiffer the axle, the stiffer the radius arms, the smaller the wheels and tires, the less likely that DW which is caused by frame flex will occur.

sidetrak06: Dude, you hung a way huge spinning mass on the ends of your spindly little E350 frame. The C channel frame can't handle this, the ball joints, the hubs, the axle spindles, the size and mass of the wheels and tires, everything is designed to be balanced. Your wheels and tires put that system out of balance. So you will get frame induced DW. In otherwords, your tire is hit, some component in your frame/suspension flexes in response, the spinning tire wants to return to spinning on its horizontal axis so the tire moves to recenter itself pushing through the tie rod and setting up the same reaction in the opposing tire.

DW is a turning event. That is why your steering wheel rapidly turns back and forth during DW. And that is why damping the tie rod eliminates DW.

3. Some of you just want the DW to stop.

Dual opposing gas pressurized SHOCKS don't put much added resistance on the steering box like dual steering stabilizers would and it eliminates DW caused by "punches" (i.e., bump steer) transmitted through the tie rod.

[sidetrak06]

I understand what you are saying about damping the tie rod. My point is that the first and most important issue to tackle is the movement of the axle, which is clearly seen in video #9 to be happening in the bushings of the radius arm. This movement will force a turning radius onto the steering system:



As the axle moves fore and aft, the vehicle reacts by turning right, left, right, etc. until the movement in the axle stops, which stops the DW. I am sure I could reduce the effects of this reaction to axle movement with dual steering shocks, but that is not the goal...yet. I need to keep the front and rear axles parallel throughout suspension travel. Once this is accomplished I am not fighting an inherent issue of random steering angles being introduced.