600 Megawatts

LOL ! I just wanst sure how dodge intended them to look.!!!


Cowhand, draw the force diagram for yourself, as soon as you do, it will become clear!

With the rods stacked as I suggested, its not more leverage on the knuckle because the forces are in OPPOSITE directions....


KP

Eskimo

Either system is flawed. Heims should be captured in double shear.

The ideal method would be to weld another bracket off the front of the knuckle (since we don't have kingpin knuckles that make this easier) so that the bolt would be in double shear, and the drag link would be on top of the tie-rod, which IS the proper setup.

Bending a tie rod or drag link intentionally is NEVER a good idea. All tubing is weaker once bent.

This is all moot anyway - heims are not meant for street use, unless you enjoy them wearing out as quick as your trac bar.. I use a very similar system to the OEM Dodge setup on my rockcrawler, and it works very well, and allows for more axle movement before binding than any suspension system made for our trucks will allow...

Cowhand

Agreed, heim should be captured in double shear, but trying to weld a bracket onto the knuckle to capture the ends probably wouldn't be a good thing...

Eskimo, we've had this conversation before... So far my heims have far outlasted the OEM style TRE's, but IIRC, your experience was the opposite. As far as bending the tubing, I'll agree it make it weaker, but with 1 1/4" .250 wall DOM I don't think it's much of an issue.

600, I've seen several knuckles broken off at the end because of the "correct" set up as you believe. That set up works great in double shear, but force diagram or not theory and practice are two different things.

600 Megawatts

Eskimo, you are absolutely correct.

C.H., No problem, dont want to argue, but force diagrams ARE real life.



KP

BigBlue

Force diagrams, schmorce diagrams, the thuren setup looks a lot cooler.

Crimedog

I see wha megawatt is saying. If you put the drag link on top of the knuckle and the tie rod on the bottom, the drag link will put force towards the passenger tire (during a right hand turn), and the tie rod will be pulling the other tire over, casuin the force to be towards the driver side tire. This puts twisting force on the knuckle. Enough to break? Who knows. But what he is saying is put your drag link on the top of the knuckle, underneath the tie rod. Maybe not the easiest, but the most practicle. Like you say, if the drag link gets too far away from the knuckle it gets a lot more leverage on it, this is why it has to stay close to the knuckle.

Now when you make a right hand turn, the drag link will put force towards the passenger side tire, the knuckle will put force in the opposite direction (because it doesn't want to turn), and the tie rod will also put force in the direction of the driver side tire because it has to drag it over. This makes one force push perpendicularly against, and in between two opposite forces. Kinda like taking a pipe holding it in both hands and pushing on it in the middle with your foot. It is a lot more stable. Now if you take one of your hands off the pipe it is not stable at all. Maybe that made a little sense...

I guess that I see the knuckle as being strong enough to handle the twisting force of the regular x over steering, but with both mounted on top it becomes less twisting force.

600 Megawatts

That is exactly correct crimedog


KP

Eskimo

There's a reason why the OEM trac bar is solid... 1.25" OD .250 tubing is not that bend resistant... It's got the same resistance to bending as 1.5" .120, or 1.75" .085 Going to 1.5" OD .250 almost doubles the bend resistance.

This refers to a STRAIGHT section of tubing. Bend it, and those numbers go WAY down.

It's amazing how outer diameter affects the strength of tube so much more than thickness. I've found this out with the numbers, and also in bending tube for cages when our bender was manual.

I've learned alot of neat, useless trivia about the subject since I started messing with linked suspension design.

YMMV, and you may NEVER have a problem... The steering on my rockbuggy is 1.5" .250, but you better believe the links will be 2" OD, .375 wall.

walexa

600, you are correct about twisting action, but is it really relevant here? I've been to school, know all about force diagrams. If you want to look at force diagrams, you need to use a modelling program to model the knuckle and apply realistic loads on it to see the stresses in the knuckle. The knuckle should've come from the factory with a safety factor of 2 minimum, possibly much more. I have not heard about any breaking or cracking. You can say "well if it broke, I would feel sorry for the people in the truck", but apparently they aren't breaking with people like cowhand subjecting the steering system to much more force than the average joe would. The distances (moment arms) created by the thurenfab system aren't tremendous, and that should be taken into account. The closer to the knuckle that the heims are, the more the unit acts as a single point load. I guess I'm just saying that although I love my truck, there are lots of things that aren't perfect, so why try to nitpick something people aren't having problems with. Just my opinion.

Waylan

600 Megawatts

Eskimo, you are right, its all about diameter baby !!!

Walexa, yep, I can't argue with anything you said. I am sure there is a safety factor there, I just dont care for using up 100% more of it than stock on a steering component (but I have no problem doing it with the engine ). And your right, no ones breaking them now, but I would be concerned with fatigue life, and as you know, we have to wait a bit for that to set in....


KP

Cowhand

Granted outer diameter has a big effect on strength, but it seems obvious to me that sizes being equal, wall thickness has a greater significance. I'd much rather run my 1.5" .250 wall than .125 wall. Duh. For that matter, I'd rather run the 1.5/.250 wall than 2.5"/.085 or .125 wall if it's subject to rock dings. Once it's dinged, the thin wall tubing goes down drastically in strength. I've learned alot in the last year about linked suspension as well, enough that I ditched the 4 link and went to radius arms, but then I'm not looking for articulation for crawling.

And I would imagine that the biggest reason the factory track bar is solid is because it's cheaper material and labor wise to cast a bar rather than bend and weld DOM tube.

THURENfab.

you guy's are funny....

a few notes to ponder before people start to listen to and adopt these "facts"?

*steering links and supension links are like apples and oranges. Supension links need to withstand MASSIVE shock forces where steering links take a more "push-pull" force. Just look at a typical steering tie rod end for it's absolute strength and it's not really worth much. Would you use that same TRE on a suspension link?

* The heims I use on my steering kit's COULD be used as a suspension joint, and are NOT the cheapo $13, mild steel joints. Use a small heim as a suspension joint and it will wear out fast, use that same joint for steering and it will last a LOOONG time...

* like mentioned, tube diameter is the most important thing, when it comes to overall strength. The stock dodge SOLID track bar is 1.25" diameter as my track bar is 1.75x.25 wall tube... MUCH stronger with a more mild bend as to resist bending even more... I don't think there is a need to discuss the stock 1" steering's bending resistance...

* my steering kit's are 1.5x.25 DOM..... just try to bend it without bending more important things. Any heavier duty, and it would be just plain stupid on a steering part.....

*now probably the most important issue here...... The whole deal with force/stress models on the stacked heims, vs. heim-knuckle-heim, stock TRE, etc... It is sort of irrelevant, when you take into account that the stock TRE has a better chance of wedging/twisting itself through the tapered hole, and breaking the tip off the knuckle. I have seen this happen along with snapped TRE's way more often than snapped knuckle housings. I agree that the dodge knuckle is not the most heavy duty but I can say that the pitman shaft will snap way before the knuckle.... I wouldn't go full hydro with a stock dodge knuckle but running any type of heim setup has been proven absolutely fine...


Don....

HOHN

Conrad, why go radius arm in lieu of a 4-link? Wouldn't the more-constant caster curve of a 4-link be desirable? Or is the Dodge execution of a 4-link such that it makes it inferior to a radius arm?

I mean, I picture a SLA independent suspension and how it can be dialed in to deliver ANY camber curve you want. A shorter top arm give more negative camber as the suspension compresses. Conversely, a longer top arm would give more positive camber as the spring compressed (I dunno why you'd ever want that, but that's not the point).

So, returning to CASTER, wouldn't a 4-link be more desirable in that the caster curve could be dialed in EXACTLY by adjusting the length of the links and the relative locations of where they attach to the frame? If both links attached to the frame at points that were within the same vertical plane (i.e. one directly on top of the other), wouldn't caster be constant throughout the suspension travel? Or you could make the top link shorter and have more positive caster as the springs compressed, couldn't you?

Just curious as to why you favor the radius arms. A friend has radius arms on his jeep that has a custom fabbed triangulated 4-link.

Check out www.tntcustoms.com for examples of his y-link style radius arms.

Justin