|
Death Wobble cause?
I started a new thread as there may be several out there regarding the 'Death Wobble', I did not want to exclude any...I am only somewhat familiar with the total content of the threads as I am a latecomer to the topic...BUT, I was reading the 2019 Ford SuperDuty brochure, the section about the fully boxed stronger frame, being 24-times stronger than that of the previous generation, and this statement caught my eye...refer to the excerpt in this thread, perhaps the 'older', 'weaker' 'more flexible' open channel frame performed a function when a particular dynamic was occurring, perhaps it absorbed what is now being transferred to the 'only other' 'flexible' components of the underpinnings, the wheel/steering/suspension system...Ford specifically mentions improved RIDE and STEERING as benefits (aka CHANGES) to this new Super Duty, perhaps in reality it's not going as planned resulting in 'Death Wobble'...any thoughts? [not sure if an image or link will appear for my visual aid]
https://cimg9.ibsrv.net/gimg/www.for...7b5a73d64d.png |
I have never experienced the death wobble on my 2017 F-350. They said that about my last F-250 and I never had a [roblem with it either.
|
I personally dont believe “frame beaming” necessarily would be the cause of a wobble. Now bad parts, bad tires, bad alignment combined with frame beaming and you could have a problem. Personally i think ford has had a bad batch of mis machined suspension parts. I am leaning towards mis machined tapers on the pitman arm where both the track bar on the 4 wheel drive, and the centerling on the 2wd are attached. I started a thread last night “first post lil’help here” because i am having a chatter problem with my f250. I had it fixed and within 500 miles it has returned. It is not a death wobble, but it shows precursors for it. Its like an uncontrolled undulation in the steering wheel when driving over ruff pavement. If you want to read my story check out my thread. I have a 2 wheel drive so my suspension parts are different, but it is still an “old school” steering system with center linkage and a steering box. The style of steering on both the 2 and 4 wd trucks will be susceptible to “death wobble” under the right circumstance. If frame beaming were the issue i believe that “death wobble” issues would be more wide spread. |
It’s a clear combination of unspeuung weight, vibration harmonics and bad alignment issues. Predominantly caster. If you read up on some of the threads, and there are some techs that have posted the alignment spec sheets it’s all about getting the caster on both sides with proper shims. Every piece is manufactured, and every piece is built to tolerances, the wrong comibination, and the only way to spades the issues is camber shims to get out to the +3-4 degree mark on both sides. To get the proper set up, a technician or mechanic needs to know their work well. You want to see the detailed print out before and after this work, and when the issue is corrected, you want the print out of exactly what all the settings are. my 2005 had 4 alignments in its life, I wish I had those sheets to show you, but the only time I experienced this was after a long run on old tires, worn out, and ready for new and an alighpnment. Every time, the same tech, minor adjustments, and everything back to normal. Don’t cheap out whenever you put on new tires, the teuck should be checked for alignment. Not just that it’s in spec, but where exactly for all specs on the report. so far, 2017 is not showing any signs, just put new tires on, full alignment at 41,000 Km. They didn’t have to change a thing. if your lifted or levelled, this gets even more complicated, heavier tires, wheels, lift, should require all new alignment parts, adjustable track bar, and even more important a tech really knows what their doing. hope this helps, I am not a mechanic, or a tech, but I do read a lot and haunt these forums. If I can help, I will if you have more questions. |
Thanks mhoefer, that makes sense, the ‘stacking of tolerances’ agravating the situation...I am awaiting delivery of my 2019 crossing my fingers...thanks for the thorough explanation. |
All mechanical assemblies have a resonating harmonics, that includes the steering gear and front hub and wheel assemblies of a vehicle. Because of the nature of a beam axle and the rather large and heavy front wheel/tire/hub assemblies they have a rather low frequency for that harmonic and considerable inertia. Worn steering gear components, or components that are at the loose end of the tolerance range, allow for the natural harmonic to continue its oscillation after an initiating event, like a bridge expansion joint.
It is caster, and its resulting "trail" (the distance between the point where the steering axis intersects the ground the contact patch of the tire), that provides the stabilizing force to the steering gear and prevents the natural harmonic/oscillation to continue after hitting a bump. Its the same principle that stabilizes the front wheels (casters) of a grocery cart when in motion. These trucks don't have much caster to begin with. And if your caster setting isn't maxed out then the stabilizing load from caster is reduced and the steering gear and its steering stabilizer are forced to take most of the load. That load will ultimately wear, or damage, the steering gear and steering stabilizer. Those damaged parts, with the resulting slop, allows for more un-checked oscillation and that is what causes the "death wobble". The fix is to replace any of the steering gear components that exhibit any slop and max out the caster setting. If I remember correctly, the factory caster spec is something like 3.8 degrees. If you get one of the kits I would set it at 4.5 degrees or even as much as 5 degrees. edit: Incidentally, a stiffer frame (or chassis) will always result in improved ride quality and reduced NVH (noise, vibration and harshness) because the frame is an undampened spring. A suspension impact is transmitted to the frame through the suspension, springs and shocks. The frame then flexes and rebounds. The bigger the hit the bigger the flex and the more cycles of rebound. A stiffer frame reduces the amount of flex and rebound (amplitude) and the number of cycles that occur after the event. The stiffer the suspension (springs and shocks) the greater the load transmitted to the frame/chassis and thus potential for flex. The stiffness of the frame only has a slight effect on what we call death wobble because death wobble is the harmonic of the steering gear and wheel/tire/hub assembly and not the frame. Although the steering gear ultimately mounts to the frame so there is some effect. |
What confuses me is if increased caster helps then why is ford reducing it to the minimum spec range in step 7 of the tsb? |
Originally Posted by Clubwagon
(Post 18363207)
All mechanical assemblies have a resonating harmonics, that includes the steering gear and front hub and wheel assemblies of a vehicle. Because of the nature of a beam axle and the rather large and heavy front wheel/tire/hub assemblies they have a rather low frequency for that harmonic and considerable inertia. Worn steering gear components, or components that are at the loose end of the tolerance range, allow for the natural harmonic to continue its oscillation after an initiating event, like a bridge expansion joint.
It is caster, and its resulting "trail" (the distance between the point where the steering axis intersects the ground the contact patch of the tire), that provides the stabilizing force to the steering gear and prevents the natural harmonic/oscillation to continue after hitting a bump. Its the same principle that stabilizes the front wheels (casters) of a grocery cart when in motion. These trucks don't have much caster to begin with. And if your caster setting isn't maxed out then the stabilizing load from caster is reduced and the steering gear and its steering stabilizer are forced to take most of the load. That load will ultimately wear, or damage, the steering gear and steering stabilizer. Those damaged parts, with the resulting slop, allows for more un-checked oscillation and that is what causes the "death wobble". The fix is to replace any of the steering gear components that exhibit any slop and max out the caster setting. If I remember correctly, the factory caster spec is something like 3.8 degrees. If you get one of the kits I would set it at 4.5 degrees or even as much as 5 degrees. edit: Incidentally, a stiffer frame (or chassis) will always result in improved ride quality and reduced NVH (noise, vibration and harshness) because the frame is an undampened spring. A suspension impact is transmitted to the frame through the suspension, springs and shocks. The frame then flexes and rebounds. The bigger the hit the bigger the flex and the more cycles of rebound. A stiffer frame reduces the amount of flex and rebound (amplitude) and the number of cycles that occur after the event. The stiffer the suspension (springs and shocks) the greater the load transmitted to the frame/chassis and thus potential for flex. The stiffness of the frame only has a slight effect on what we call death wobble because death wobble is the harmonic of the steering gear and wheel/tire/hub assembly and not the frame. Although the steering gear ultimately mounts to the frame so there is some effect. DW is the result of reciprocal motion, on a horizontal plane with ever increasing harmonics as a result of slop in 1, some or ALL suspension components. If you truck was aligned properly to begin with and you have kept your components within OEM specs and you don't much in the way of off road travel or using the curb to stop instead of brakes the Alignment plays a less important role, that said the first thing I recommend is that alignment be checked and wheels balanced and proper air pressure (mostly to eliminate them from the search). DW is more prone on front axle (4x4) vehicles, but almost any vehicle can suffer fro DW and until you have gad DW on a motorcycle at highway speeds you don't know what scary is. Generally is the result of worn components from shocks to ball joints and everything in between. More often than not it begins at a worn track bar and a failing steering component shock, which is the job of the shock to mitigate the reciprocal motion. It's frequently easy to fix if and when you can isolate the component(s) that contribute to the slop. Alignment and tires in spec and replace the Steering stabilizer, then see if you still have the problem. Generally if your vehicle is OEM that will fix it. Throw on a set of huge tires and lift kits then all that has to be dialed in to compensate for parameters outside of OEM specs. |
Originally Posted by Uzumati
(Post 18363843)
What confuses me is if increased caster helps then why is ford reducing it to the minimum spec range in step 7 of the tsb? If you are experiencing DW on an OEM truck and alignment and tires were in spec the my first action is to replace the Steering Stabilizer more often than not this solves the problem, next step is the track bar after that we are grabbing at straws until we get the right one. I look for a weak front shock, bad ball joint and a worn out rubber bushing. I have never not fixed it when a vheickle came into my shop and most often is been a major challenge because 99% of the vehicles carried large ties and lifts. |
everything ive read about stabilizer location would suggest ford made a mistake by mounting it to the drag link
|
I have just 600 miles on my F350 Super Duty Platinum model. The tires felt out of balance from the get go and very often I will feel what I consider a mini Death Wobble in the making. I have been waiting two weels for the parts of TSB # 18-2268 to come in. |
Originally Posted by andybull
(Post 18364288)
I have just 600 miles on my F350 Super Duty Platinum model. The tires felt out of balance from the get go and very often I will feel what I consider a mini Death Wobble in the making. I have been waiting two weels for the parts of TSB # 18-2268 to come in. |
Originally Posted by 17 Oaks
(Post 18368860)
Do you have a link to TSB # 18-2268??
Jim |
Originally Posted by Uzumati
(Post 18363843)
What confuses me is if increased caster helps then why is ford reducing it to the minimum spec range in step 7 of the tsb? https://www.ford-trucks.com/forums/1...l#post18355185 I get all the arguments about more caster, but I don't see anyone on this forum with a truck under 12-15k miles with DW solving it with 4.5+ degrees of positive caster. |
Originally Posted by TXKR
(Post 18368889)
No one can explain this to me. I am currently bypassing the dealer and working this my way in this thread:
https://www.ford-trucks.com/forums/1...l#post18355185 I get all the arguments about more caster, but I don't see anyone on this forum with a truck under 12-15k miles with DW solving it with 4.5+ degrees of positive caster. That said this begs the question of why to you increase caster to stop DW??? Bigger tires is the reason. Bigger tires, bigger contact patch, same goes for low air pressure. The parameters of the OEM suspension are fairly tight and when any mod is made that changes those parameters it can sometimes have a roll thru effect meaning that it impacts other parameters. Remember that suspension is a lot of complex angles interacting with each other. Change one, you often have to change others. |
| All times are GMT -5. The time now is 01:24 AM. |
© 2024 MH Sub I, LLC dba Internet Brands