DW! Need longer arms for more caster

[HLewallen]

As stated in another post - just had my first Death Wobble experience. Running BFG 315s (probably not for much longer) with DRC Race. Just got out of the alignment shop (same one that aligned after the KORE install) and found out the truck is maxed out at only 2. 5 degrees of caster! I guess they forgot to mention that the first time.



Does anyone know of aftermarket trailing arms for third gens that are longer so I can get some more caster? And please don't say KORE - yes those are very nice and I would gladly accept a donated set, but WAY over budget. Tubular and adjustable would be nice.

 

[rbattelle]

DT Profab makes a set that are 1/2" longer (P/N DTP 02008). MUCH cheaper than Kore; not tubular.



-Ryan

 

[HLewallen]

Thanks Ryan. I could not remember the name of those guys! They are checking into it, but back of the envelope calculations say a mixed set of their stock and +1/2 inch trailing arms should give about 3 degrees caster. They are checking into it for me. Hopefully someone at their shop has tried this before.

 

[BHanna]

My ProComp lift with new control arms maxes out at about 3 degrees of caster but I've never had any DW problems. I think they decrease the caster to decrease steering effort. I've been a little nervous about so little caster and have been checking around for longer arms too. My local 4-wheel-parts place says they have some new adjustable ball joints that can increase the caster but I haven't had them put in because I haven't had any problems yet.

 

[Diesel Nut]

Before things get outta hand, I would chect the track bar. I had the death wobble once only after intsalling the spacers and it was a bolt that had broken off mounting the track bar to the axle. Just thinkin and tryin to help out.



Also, and correct me if I am wrong, I don't see caster or camber affecting this. The death wobble is caused by the axle movement in its upwards or down travel having slop (track bar or bad bushings) being able to move around with the steering wheel not moving, making the tires jerk left to right rapidly and violently. I would be looking at what keeps the axle located before I worry about alignment. My 2 cents.





Also, when that bolt let loose, at a stop I could turn full crank either wy and the front end would shift to one side, not steer the tires. I think there is more to this than trailing arms. If not, I learned something new. Cool. Good luck with this, I know how it can rattle ya!

 

[KBertetto]

It sure seems like a lot of folks that get the death wobble, have those BFG 315's. My buddy has a 03 2500 hemi 4x4 with those tires and he said he had it happen to him last week, not sure what he plans to do about it. I'll fill him in on the whole caster dilemma, and to also check all bolts on the underpinnings. He only has 20k miles on the truck, (1k on the 315's), completey stock otherwise.



Bert

 

[BHanna]

I've got 20,000 on my BFG 315s, no DW, and way over half the tread left. Lots of posts attributed the DW to caster reduction but mine is just under 3 degrees and I haven't had it. The track bar could be the problem. I'm going to check mine a little more often just to try to keep the DW away.

 

[kentkroeker]

I would be very careful about adjusting a lower control arm to a position longer than stock. If you do this even . 25" relative to the upper control arm, with the caster mark on the eccentric set in the vertical position, you will have serious front driveline vibrations above 45 mph. On 3rd Gen trucks, if you adjust both arms . 5" longer, you may run into bind on the pitman arm at full-lock left steer as well as interference with the drag link/tie rod intersection at the passenger-side end link mount - and you won't increase your caster angle. In addition, you may exceed the extension capabilities of the front driveshaft. It may work for a while, but there probably isn't enough overlap for long-term reliability. We've tested all this, so that's how we know.



It's been our experience that DW usually has something to do with worn or defective steering components or inappropriate tires. I would inspect these parts before changing caster. When we raced the Baja 1000, I set the caster on that truck to the full minimum position - hash mark on the eccentric facing aft. This equates to roughly zero degrees. I just like the way the truck steers with very little caster. It would never DW unless certain braking bumps caused the stock power steering pump to cavitate because fluid flow became intermittent. We solved this problem by adding an extended reservoir to the power steering pump. Point being that the DW we were able to induce was a steering issue, not a geometry (caster) issue.



That would also explain why certain trucks DW right off the showroom floor. They have a bad drag link, tie rod end, steering box or track bar.



Hope this helps.



Cheers,



Kent Kroeker

 

[Doubleclutch]

Permit me to quote Dieslman's research here:

08-21-2005, 01:04 PM #20

DIESELMAN

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Quote:

Originally Posted by Bertram65

That is fine, but as long as the front of the truck sits higher than it did before the suspension was installed without longer control arms the geometry is altered, the front suspension moves in a arc, the lower it goes the further back it comes tilting the axle forward at the top as it goes. I have the snow plow prep on my truck, I have run BFG 315s and had no problems on stock suspension, I still say there are very few who have had DW with stock suspension, I did not say none, just very few, if you read about it here it is probably pretty accurate to say 90% of the poeple who have had it have altered suspension.





I've had DW with stock suspension, and lifted suspensions, and cured it.



As to geometry, not Exactly, this is true of the FORD front suspension with a SINGLE trailing arm, Dodge has 4 links. On a ford the axle rotates so that lowering the axle (lifting) rotates the axle forward, decreasing caster and necesitating dropped trailing arm brackets equal to the drop of the axle(lift).



On our dodges, the axle is trailed by four links. on each side there is a link above and a link below the axle, these trail back to frame mounting points that are about the same distance apart as they attach to the axle. The effect is that as the axle moves down the lower arm 'pushes' the bottom of the axle tube forward, and the top arm 'pulls' the top of the tube rearward by the same amount, the caster angle does not change.



Now the true geometry is improvised a bit as the spacing isn't the same at both ends of the links, the lengths of the top and bottom arms are offset to account for this and there is a bit of bias so that the caster angle will increase on compression which aids in return to center feel when you are driving over curbs and such.



The actual loss of caster even at 4" of lift is only about 0. 5 degrees, no where near enough to cause DW. (An old Ford F150 swung +/- 5 degrees!).



DW is caused by worn ball joints, tie rod ends, track bar, steering gear, soft or uneven sidewall pressures or stiffness ( want DW, put on BFG 315's and stagger the tire pressure 10 pounds).



Lifting keeps the caster roughly the same, pulls the axle rearward (looks wierd in the wheelwell without extending the trailing arms, really high lifts run out of bar angle/range and need dropped brackets, but not at a resonable 4" lift) and shifts the axle to the side (also strange if you don't change or drop the track bar, but the axle moves side to side during action anyway so the adjustment is only for looks at ride height), and dropping the track bar requires dropping the pitman arm to maintain absolute parallel alignment of the steering and track bars to prevent 'bump' steer.



However, factory alignment sucks and so do most alignment shops. The Caster Cams allow the axle to be twisted all out of proportion causing excessive cross camber caster angles even when overall caster is correct, and tramlining or uneasy feel on a crowned road. If you can't drive your stock truck comfortably with one finger, repair whats wrong, re-align it, then lift it. Don't lift or add 'performance' components to cure the problem or you'll be chasing your tail and cussing your vendor because it will amplify the problem.



DM

__________________

2004. 5 3500 DRW LWB QC 4X4 600 6 SPD LARAMIE

2830RL FW with 2. 8Kw Outback Inverter/500W Solar/MX 60 MPPT/550AH of Battery - Totally UnPlugged!

He sez it much better than I could.

Greg

 

[rbattelle]

Wow, Dieselman really puts things nicely!



-Ryan

 

[MickeyMiller]

I don't want ot jinx myself, but I have 55K miles on my '03 4X4 Quad Cab SB. The last 47K miles with BFG 315s. Rotated, front to rear, every 6K mile, 50 lbs. front, 40 lbs. rear. No DW, nice ride, good traction for the mild off road that I do. I think I still have 10 K on these tires.



Anyone have any feed back on the ride quality of the Toyo 35 X 12. 50's? That's the other tire I am considering, but I'll probably stick with the BFGs.

 

[HLewallen]

Kent, I am seeing some inconsistencies here. On your site I seem to remember something about getting an alignment before you install KORE suspension, becasue sometimes even stock dodges cannot be aligned correctly. That would seem to imply alignment settings are important. It also describes my truck - the modified suspension geometry could not cause a change of 2 degrees in caster, so obviously my truck wouldn't align stock. What I am confused about is your coments concerning lengthening the lower arm being a bad thing. Isn't that the point of the eccentrics? By my calculations, lengthening the lower arm by . 5 inches would result in about 2. 75 degrees more caster - which would just barely give me enough range of adjustment to get to the factory 4. 5 degrees of caster. Could you be a little more specific about the driveline vibrations? Are you talking just due to front driveshaft angle? Why do you think the caster will not change with a longer lower arm? Once again - isn't that what the eccentrics are for? To lengthen the distance between the mounting points of the lower control arm to adjust caster? You are mentioning a lot of places where the suspension interference could occur and saying . 5 inch will do all of this. Is this at full stuff/droop? Maybe on your truck - but are you taking into account the tolerance stack up during manufacturing that led to my truck having very litle caster in the first place? These interferences may or may not occur - it depends on where the truck to truck differences lie in the suspension. Either way, on my truck, lengthening the lower arms will be putting my truck closer to average stock geometry in caster.



Dieselman's writeup references modified suspensions only losing . 5 degrees of caster due to lift, and this not being enough to cause DW. That would imply that caster can indeed play a role if reduced by more than . 5 degrees. Note that 2 degrees (my truck) is much more than . 5 degrees.



I had the alignment shop (PAB here in Tucson) check all the front end components when they aligned it because I didn't want Dodge telling me they are "in spec". They said the entire front end is very tight - the only play they could find was a miniscule amount in a tie rod end that was well within anyone's spec. They said they wouldn't have even mentioned it if I hadn't been overly concerned, and suggested changing it as a last resort. Are these things that unstable? Kent, you may change components all the time on a race truck. Is it not plausible that "street" trucks are spec'ed 4. 5 degrees of caster to keep them from reacting badly to mildly worn front end components?



I wouldn't carry a firearm that could suddenly become uncontrollable.

I wouldn't use a powertool that could suddenly become uncontrollable.

I sure ain't driving my truck right now.



I appreciate the help in figuring out my course of action. And as I tried to imply in my first post - I am trying to find some E rated tires. I hope someone buys my old Power Wagon soon or I will be eating cereal and PBJ for weeks.

 

[Greg Boardman-RIP]

I know that people do not like to hear about the BFG tire having a play in DW but it surely does. I have tested it more than once on my truck by switching tires out to the 315's. It is like taking a DW pill. 65-70 mph and the right bump and DW... Instantly with only a change of tire. I have reciently replaced every componant on the front of my truck. Except the steering box. I wouldn't put those BFG 315's back on a truck if you gave me $10,000 cash. NO WAY!!! Go put a set of new tires on your truck Heath and your DW will Dissapear. If you want, bring it out to the DRC compound and I will personally chase down the cause of your DW and show you how to fix it for NO CHARGE... If parts are needed, you will of course, be charged for them. But I will not charge for my labor as long as you get a new set of Load Range E Tires... .





Greg DRC

 

[JayWm]

Greg, do you a theory on why the BFG's either induce or are susceptible to the DW. It appears that you have spent a lot of time researching this issue and I'd like to hear your thoughts. If you prefer to take it offline shoot me a pm.



Thanks,

Jay Williams

 

[Greg Boardman-RIP]

Jay,

It is no secret that we have an idea about how the suspension works on these truck. I have worked long and hard to understand the DW phenomenon but still I cannot tell you the cure. It is a progression of failures, in small increments, that combined with a "special" type of bump cause the front of our truck to dance like a basketball in a final four game. I am sure that the BFG has an issue that is deep inside the flimsy sidewall or the underrated tread. It is designed for GM to fit the stock H2 truck platform. That is a 1500 Silverado, not a 3500 Ram with a Cummins. It for some reason does not hold up to the abuse of a heavy truck. The sidewall gets soft, and then it cannot supply the support needed to deflect the DW as it occurs. I wish I could give you a better answer but that is it.....

Greg DRC

 

[kentkroeker]

HLewallen,



You're correct when you say that the eccentric on the lower control arm changes the control arm length in order to adjust caster. I may not have been clear when I discussed the consequences of lengthening the lower control arms independently of the uppers. If you lengthen the lowers you will increase caster. But from our testing, . 25" will increase it beyond the comfortable limits of certain parts, one of which is the front driveshaft's u-joint. We were testing a couple of things last week to address certain issues related to a new project, so the effects of our experimentation are still fresh in my mind. We didn't calculate, we measured. And what we found was that a . 25" increase in lower control arm length relative to the upper control arm yielded 6. 5 degrees of positive caster with the hash mark on the eccentrics set vertically. We collected this data from a single truck. This was not an average we derived from many trucks. However, we measured this truck for factory abberations and found it to be within our pre-established mode. For determining certain production dimensions for our parts we like to focus on the mode instead of the median, since large variations from the factory are common. Using mode (the most commonly occurring dimension) is the best when you're mass producing parts, since median (average of magnitude) can be very large. It has to do with how much beer the guy on the assembly line drank the night before or what kind of mood his wife was in that morning.



But I digress. The issue is DW and DW probably isn't going to be cured by adjusting your caster. Caster gives your truck stability and return-to-center. It also affects several other geometric properties of steering. But I wouldn't focus on this to solve your problem.



A lot has been said about running E-rated tires. As we've learned, the E-rating is a measurement of sidewall strength/flex and not simply load rating. An E-rated tire has a stiffer, less compliant sidewall than a D-rated tire.



We know that some trucks DW because of bad components. This explains why some trucks DW from the showroom. We also know that some trucks DW because of bad tires - "switched to Hummer takeoffs and now I've got DW. " In addition, proper tires mask the effects of bad components and proper components mask the effects of bad tires. This explains why some trucks never DW, even with D-rated tires.



So far, nobody has explained precisely why the tire with the weak sidewall can cause DW. We just know from experience that that switching to a better tire can cure it.



Now I'm going to totally geek out:



As your suspension moves up and down (lifted, long travel, or stock) your toe changes. You get an increase (positive) on the down stroke and a decrease (negative) on the up stroke. That's just how your suspension works. A stiff sidewall with a narrow contact patch (OE tire) or the Rickson 19. 5 set up is inherently anti-DW because, even in a high traction situation on pavement, the tread is permitted to rotate slightly around its axis as toe changes during normal suspension cycling. Now, switch to a larger contact patch - the number 315 comes to mind - that's width in millimeters - and a weaker sidewall - the letter "D" comes to mind - that's "ply rating. " Anyway, now you're increasing traction while simultaneously decreasing sidewall stiffness. The result is that instead of transmitting the rotational forces of toe change to the tread, the tread stays planted under 4660 lbs. (front axle - 3rd Gen. ) of diesel beast and every bit of that rotational force gets distributed into the sidewall of the tire. Next you get a harmonic that develops in the sidewall that spreads into your steering and throughout the entire vehicle - DW. Interestingly, it's nearly impossible to get sidewall-induced DW while off-road in low traction situations. The low friction coefficient of good old dirt permits the tread to rotate, so the sidewall doesn't have to bear the brunt of toe change.



We're off-road guys so we like large diameters for ground clearance, wide treads for traction, and thick sidewalls for durability, flat resistance and to protect wheels from rocks. But over time, even tough sidewalls can get pretty beaten up. Boardman once showed me he could make a set of clapped-out E-rated MTR's DW predictably just because he had hammered their sidewalls enough to turn them into mush. And believe me, the MTR is a good, tough tire with a gnarly, thick sidewall. But thrash it enough under the weight of the mighty Cummins and eventually they'll squeal like a room full of schoolgirls. So he switches to a new set of Coopers and instantly, with no other change, the DW can no longer be induced. Figure that one out. We'll have to see how long they hold up. That's another element we're experimenting with - we're currently finding out that not all D-rated tires are weak sisters. Some D-rated tires are holding up pretty well to some serious abuse which leads us to believe that either not all D-rated tires are created equally or DW being most common to one brand and size is relative to the fact that the preponderance of consumers choose that particular tire as an aftermarket replacement.



Here's the point to all this: As you go up in tire size, your contact patch increases. Correspondingly your traction increases thereby necessitating an even stiffer sidewall to transmit normal suspension and steering movements to the ground where they can be dissipated harmlessly instead of into your vehicle where the effects are manifest as DW.



Combine this tire phenomenon with a loose tie rod end or sloppy drag link and you get a pretty scary truck - a truck even scarier than Boardman's off-road driving.



That's what we know so far.



Best Regards,



Kent Kroeker

 

[HLewallen]

Greg - yeah, I know you would help out. Thanks for the offer.



Kent - Ooh - I love it when you geek out Kent. It gives me goose bumps. But speaking of scary driving, how many times has Greg rolled his truck?



Experiment/experience is always better than theory. 6. 5 degrees! With a 1/4 inch? Dang. So much for that idea.



I wouldn't say I'm a firm believer in the BFG 315 causing DW (natural skeptic), but I do think the correlation is too high to ignore. I won't be running them anymore. I will also be acting on the assumption that sidewall strength (and sidewall strength over the life of the tire) is an issue. I have also heard (so rumor only) that the MTR's sidewalls can degrade over time/abuse. What Cooper are we talking about guys? I am trying to find tires right now, but I am going through my Uncle as a courtesy (and because of the discount). He of course can't get 35/12. 50 r17 Toyos due to backorder, so we are investigating other options. TrXus MT is next on the list. Question for you guys - he can also get the 37" Toyo. A long time ago when I was investigating KORE suspension, I was told minor trimming of the plastic inner fenderwell would be necessary to run that tire. With more time and experience now, I would like to ask again how bad of an idea would it be to try to running that tire on DRC Race with stock wheels and 4. 10s? Even if they fit can the brakes handle them (not heavy towing)?



Thanks guys.

 

[kentkroeker]

Heath,



Believe it or not, rolling my race truck was actually less scary than sitting in the right seat of Big Red while Greg once did 70 mph over a blind, MX-style step-up jump at night. I say to him, "Man, I never drive like that - even when racing. " Then I ask, "What if there was some kid on a bike coming up that hill from the other side?"



Without missing a beat, Greg says, "That kid would be dead. "



We have this little game we play with each other. We secretly find some nasty terrain, jump or obstacle, then go over it a hundred times until we find the very limit of what's possible to survive - both humanly or mechanically. Then we say nonchalantly, "Hey, wanna go for a ride? I want to show you something. " The trick is to hit the jump or whatever without warning the other guy it's coming. You watch him very carefully out of the corner of your eye. If he flinches, grabs the dash, even sits up straighter or, God forbid, makes some kind of little noise or squeal in reaction - he gets ridiculed relentlessly for a long time - all good-natured of course. We laugh and laugh about this kind of stuff - but there really is a certain fear factor involved. The episodes always end with one of us asking, "Well, did I scare you? Did I?" Of course the answer is always, "No, that was Nancy-boy stuff. " Then the guy in the right seat searches for something even gnarlier with which to scare the other guy. My favorite one is this eight inch curb to a four foot drop-off I hit at 60 mph - from the highway. Nobody expects it. I say, "look at that llama. " It distracts them for a second and when I launch the truck off the pavement they think the steering column snapped or something. It's so funny - we laugh and laugh and laugh...



About running those 37" Toyos - you have to do a lot of trimming to get them to work - both metal and plastic - and on the OE wheel they will rub your control arms.



By the way, the caster figures I gave you may not end up being the same for your truck - that's just what we measured on one of ours.



Good luck with everything. Please keep us informed about any changes you make and what the results are.



Cheers,



Kent

 

[blake underwood]

Heath,



My favorite one is this eight inch curb to a four foot drop-off I hit at 60 mph - from the highway. Nobody expects it. I say, "look at that llama. " It distracts them for a second and when I launch the truck off the pavement they think the steering column snapped or something. It's so funny - we laugh and laugh and laugh...



Cheers,



Kent

:--) Got any pics or vid. of that one!!!

 

[Greg Boardman-RIP]

Now you all understand here that my friend "The Mad Scientist" has an affinity for a controlled enviroment while out testing. Speeds remain the same, tires, wheels, springs, and such are not messed with. Just one part at a time. Last month Kroeker gave me a Top Secret part to put on my truck while at the KORE Compound. I was more than happy to test it with much vigor!

Off to the testing grounds and a good session of jumping the old "T-REX" Jump. As you approach the jump, sliding sideways is always a good sign of enough speed, you are advised by Mr K to only be traveling about 55 mph for optimum testing. Well, I have been known for insubordination before, we are traveling at about 70 when he says to slow down a little bit. I instantly go flat footed!! Barreling Big Red at a jump that in no way can handle the speed I am traveling. 78,79, 80... ... . Perfect! We jump into the wash and land in the take off ramp, front wheels first. In off roading we call that Casing a jump. The truck leaps into the air in upwards of 6 Feet!!! Kroeker screams " NO NO NO NO NO This does not properly represent what our products are designed for!!!" I just look at him and laugh. . I say, " You have to admit that was cool?" He repeats himself, " No No No No! I again say, " Come on you know that was the coolest thing you have ever seen... ... ?" Then a pause for the Mighty K, Laughing" That was really cool!!!" Then he proceeded to scold me about the reasons not to ever do that with a customer. My reply is always the same... ... . "Don't be a P+ssy" Ha Ha Ha!



Want a ride boys?



Greg DRC