CK5 - The Full-Size GM Off Road Community

OK guys, I'm looking for a little guidance relating to the panhard bar in a front 3-link suspension. I've been collecting lots of data, and photos and studying as much as I can stand in the books....but I'm a "visual" guy, so I decided to do some mock-ups on a front suspension so I could really understand what happens with all the links and how they all affect each other.

So far, I've come up with a set of 36" lower links that look promising. The axle end of the link attaches almost directly on top of the "old" spring perches on both sides, which gives me a seperation of ~32". The other end of the links goes up inside the framerails with a slight taper. The seperation on that end is around 24". The links are basically even with the lower edge of the framerail. The resulting side view shows the lower links have about an 8* angle on them. (Not bad for anti-squat if I'm interpreting that correctly!) <- (EDIT: That should read "Anti-Dive")

I haven't attached the upper control link yet (still trying to figure out where to put it) but I have tried a few different panhard bar combinations....starting with some very LONG ones (42"+), and slowly chopping them down to the 24" one that's in the photo below. My objective was to keep the panhard bar parallel to the axletube and to split the 12" of clearance between the axletube and framerails. I built a 6" riser off the axletube, and a 6" drop bracket off the frame. This "looks" nice, but with the longer panhard bars, it smacks the frame on compression of the passengerside tire.

As I started to understand what was happening, I shortened the panhard, until the bar could "tuck" underneath the PS framerail (which it now does) which gives me more uptravel.

One thing that I've noticed on ALL of the panhard bar setups (but to a lesser degree on the longer bars) is the centerline of the axle is shifting as the axle articulates. I have indicated the centerline in the pics (in green) so show the effect.

I'm looking for feedback on the panhard bar design.....should I give up on keeping it parallel to the axletubes (and draglink) and get a longer bar in there, or should I keep it short and just deal with the (increasingly bad) axle shift that's occurring??


DISCLAIMERS:

1. There is no upper locating link yet.
2. I am not an expert
3. These pictures show an unnatural amount of flex that I can probably not utilize due to other interferences
4. My engine has no oilpan or crank.....I know this. /forums/images/graemlins/grin.gif
5. I am having a LOT of fun playing with this, but I am willing to change this design 100 more times until I get it right.


That being said........onto the pics!


Here's the passenger side view (pretty decent angle on links):
http://www.norcalbigdawgs.net/Gallery/albums/albun65/3Link_Side_View.jpg


And here's the front view with the DS stuffed and the PS drooped:
http://www.norcalbigdawgs.net/Gallery/albums/albun65/3Link_Experiment.jpg


And here's a closeup shot showing the "short" panhard bar, and how it clears the PS framerail:
http://www.norcalbigdawgs.net/Gallery/albums/albun65/3Link_Closeup_001.jpg




Ideas and suggestions are now welcome at this time..... /forums/images/graemlins/deal.gif

Hey Greg, not sure if it would work or not but in race cars they use either a wishbone style track locator or a diagonal track locator. Just a thought, not even sure if you could make either of these clear everything properly.

That is what I have been considering. Not sure if the steeiring forces will affect it.

x

with pass side stuff your axle wants to shift a bit to the pass side as gravity takes its toll right? i know thats what the pan hard bar is, but with the frame flexing, and the axle wanting to move are you sure that what looks like about half an inch will be enough clearance?

you are no expert, and i am just starting to think about learning stuff for a linked front suspension... so you know LOTS more than i. but these frames as you know flex a lot.
Grant

x

First off, I'd like to thank you for post the pics of the mockup since it does a great job of showing the geometry. It looks like the limitations your running into are a result of having to work around a single fixed variable, the stock frame, and not a lack of knowledge of application on your part. No matter how you arrange your links, your going to end up with axle shift using a panhard bar. Running a longer panhard will reduce the shifting but never eliminate it. I'm not a fan of panhards simply due to dropout shift to one side, like getting airborn would produce whether pulling a wheelie up a hill or jumping a whoop at speed. The articulating shift doesn't bother me because it most likely wouldn't be at speed so the weight shift wouldn't be very evident.

Oh, and you think you could dirty up that garage a bit, your making the rest of us look bad!!!

x

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looks like having those 2 links as uppers will allow the lower to run in the very centre of the dif to the tranny crossmember area.

I would look to having a double draglink using an idler arm back at the ds upper link frame mount
Mr Watson stated he had tire to steering box interference that precluded that being done
doing it that way would open up your axle location possibilities
you could run a watts link with the pivot frame mounted, or any length PHB you could fit

beautiful work you are doing there

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I'm intrigued by the "idler arm" comment. This is something I don't fully understand....

Are you talking about this little beauty?:


http://www.offroaddesign.com/images/TTCK5pics/front%20suspension1.JPG


Watson's front suspension confuses me due to the steering box being so oddly placed. Now when I look at the jumble of tubing there I can't really detect what is there as a result of the new steering box location vs. parts for a conventional 3-link!!! /forums/images/graemlins/grin.gif

From what I can gather though, you seem to be indicating that the idler arm creates an "association" between the steering draglink and a conventional panhard bar?? It would appear that the ability of that idler arm to pivot, could allow for it to correct the "misalignment" of the axle from a pure PHB implementation....???

I will try to find some additional pics of the idler arm stuff and maybe build an 1/8" scale model before trying it "full scale" under the frame.

Please keep the insights coming...!!! /forums/images/graemlins/thumb.gif

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Oh, and you think you could dirty up that garage a bit, your making the rest of us look bad!!!

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THANK YOU!

my wife saw these images!

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The garage DOES get dirty....I just clean it before snapping pics. /forums/images/graemlins/grin.gif Plus, the more clutter there is, the more difficult the "backgrounds" are in my photos....it tends to make things hard to decipher.


BTW -> In case you haven't already figured it out, I'm a virgo..... that should explain a LOT! /forums/images/graemlins/rotfl.gif

Now I wouldn't have said anything, but you went so far as to face all the cans and evenly space them, and even align the spray bottles heads perfectly.. heck, you even aligned the jackstands equal but opposite.. if I'm not mistaken, each spec of dirt on that floor is exactly 3 centimeters apart from each other!!! /forums/images/graemlins/thumb.gif I have a feeling choas theory doesn't apply to you - so just build it, how could it go wrong! /forums/images/graemlins/rotfl.gif

Hey Greg, another thing I overlooked the first time I replied, you would need some kind of link going towards the rear of the truck to keep the housing from rotating the pinion since you will no longer have a solid mounting point such as your leaf springs from keeping it from rotating. This is why a wishbone set-up would work best, it would not allow the movement I am speaking of and also it would locate the axle between the frame rails. /forums/images/graemlins/thumb.gif

x

Scott,

I will refer you back to "Disclaimer #1"... /forums/images/graemlins/grin.gif

I've been talking with Triaged quite a bit about some possible designs (wishbones, radius arms, etc) and a lot of the suspension styles that are considered 4-link type solutions, tend to bind and fight each other during articulation..... Dan described it as "your axletube basically starts acting like a 3.5" swaybar..." With all parallel links (4 link) I can remove the binding, but I still need to locate the axle laterally.... (hello link #5!) and that starts to look like a real "tube farm" under the front end....especially with crossover steering and a tie rod and a driveshaft to fit into the mix. /forums/images/graemlins/blush.gif

The more I do projects like this.....the more I'm amazed by what Stephen has designed and built. This is NOT easy stuff.... /forums/images/graemlins/1zhelp.gif

Like I said, a wishbone would accomplish both problems at once, it will locate the axle under the frame and also keep the pinion pointed in the right direction. A TRUE 3 link set-up. You should try to mock that up and see how it works with all the articulation that you want.

x

[ QUOTE ]
I'm looking for feedback on the panhard bar design.....should I give up on keeping it parallel to the axletubes (and draglink) and get a longer bar in there, or should I keep it short and just deal with the (increasingly bad) axle shift that's occurring??


[/ QUOTE ]

Looks like the shift (indicated by the green line and plum-bob) is about equal when either side is stuffed. Nice and predictable when articulated. (due primarily to keeping the pan-hard bar horizontal)
Allthough, it is a different story with vertical travel. I would suspect the body shift would get annoying after the "newness" wears off.

It deppends on where your priorities are.
For "street-manners", a longer bar might work out better, even if it has abit of angle on it.
For "rock-crawling", the short bar would probably be just fine.

If you could figure out how to run a "Watts-linkage" - that'd be the best of both worlds.
I remember seeing pictures of a Watts-linkage, run horizontal, on top of the axle. Rather than the normal, vertical style. Seems like that would be the way to go, to me. Figureing out how to clear the oil pan, and steering linkage would be the difficult - to say the least.

Hmmmm.. now ya' got me thinking.
I've got way too much to do today. Now, I'm going to preocupied with this allday. Dawg-awn it !




Watching your progress with alot of interest ! /forums/images/graemlins/grin.gif

Ok, here we go...

First off, Watsons idler arm there is for the steering and not any part of the panhard bar. What he did is locate his steering box towards the pass. side and used a short link from the pitman over to the idler. What this does is allow the pivot point of the drag link to be in the same location when pointed forward as the frame end of the draglink, and his axle end of the panhard is in roughly the same location as the steering arm end of the drag link. Thus he gets rid of as much bump steer as he possible can since the axle will rotate in an arc around the draglink controlled by the panhard bar. Get it?

Next, your short panhard bar worries me. I would run the longest possible because with that short bar your going to have tons of side to side axle movement as you mentioned. But your just showing the articulation movement, if your front end droops 12" your axle will be like a foot out one side... Street cars get away with a short panhard due to the 4-6" of suspension travel, not the 12-18" your project could be capable of.

As far as a triangulated 3 or 4 link, I wouldn't run that either unless you go full hydro steering. With the triangulated system, your axle will move straight up and down when compressing and drooping. Your drag link will travel in an arc getting longer as the axle moves up and shorter as the axle moves down, thus creating tons of bump steer. It's basically the same as what happens with leaf springs but you will have a ton more travel than the leaf springs, unless you limit it and if you do whats the point?

I wouldn't run a watts link either since you couldn't get the panhard bars long enough for it to work with a super long travel system. It's ideal for the street though.

I'm going to run a double triangulated 4 link in the front of the willys like this XX but I will run full hydro steering and not have to worry about the steering issues, how come you can't run full hydro? Looks like it's going to be a buggy anyway... You could run a triangulated 3 link with the lower arms being angled in and the upper link being straight and have a vertical motion of compression and droop and not have to worry about steering linkages.

The ideal setup if I were doing it with mechanical steering would be to do a "wishbone" style setup with the steering box being under the cab with a link running to a idler on the axle so that the drag link from pitman to idler is parallel with your lower 3 link bar and has the same pivot poins, then a short draglink from idler to steering arm. It would be complicated but you would have no bump steer as well as hardly any compression/droop steering since the steering arms always stay the same length in relation to axle position.

Ok, with what you have setup so far, you were talking about your antisquat, since your working in the front this is actually anti-dive and figured a little differently but basically the same but it does need to be looked into. I'm more interested in where your roll center is and your antidive percentage. What are you using for a center of gravity?

Oh yeah, I've been working on the design for the willys for over a year now and still haven't gotten it perfect but I'm gettin there /forums/images/graemlins/rotfl.gif

x

Here is my thought on the front 3 link setup. I would first make the bottom links parallel to the frame. If they are not, as the suspension goes thru its travel the axle moves side ways and the tapered link will get longer and the other side will get shorter which induces axle steer. So if the lower links are parallel as the axle moves side ways thru it travel with the panhard it makes a parallelogram and the lower links will stay the same length. Next I would run a panhard as long as the drag link is and at the same angles. The bottom links would be about 34" long and the tops in the 28-30" range. Oh Greg don't forget about the axle's pumkin hitting the oil pan. It is real close as it is right now I bet. /forums/images/graemlins/thumb.gif

A few things to point out...

The side-to-side movement during articulation is due to the placement of the roll center (with a Panhard bar the RC is where the bar crosses the centerline of the truck). You just have to think about it the opposite way as you would with the body rolling and the axle staying flat. If the Panhard were at axle level (or the RC in general) the axle would not move side to side while articulating. If you had the Panhard/RC below the axle the centerline of the axle would move the opposite way that it did in your pic's.

To throw another wrench into the machinery the placement of the RC will affect tire clearance!

If you lower both ends of the Panhard you will be able to stuff a longer bar in there and get rid of some of the side to side movement under 2 wheel bump/droop that Borrego was talking about. That might even improve your tire clearance but will give you more body roll (which might mean a sway-bar up front...another tube to add to the farm). Bump steer wise you want to keep the Drag-link and Panhard the same length and angle.

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The ideal setup if I were doing it with mechanical steering would be to do a "wishbone" style setup with the steering box being under the cab with a link running to a idler on the axle so that the drag link from pitman to idler is parallel with your lower 3 link bar and has the same pivot poins, then a short draglink from idler to steering arm. It would be complicated but you would have no bump steer as well as hardly any compression/droop steering since the steering arms always stay the same length in relation to axle position.


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the idler on the axle would be the ds steering knuckle, end of complication.
just please point to the source of a modern, available, sized to our application, steering box with a near vertical input for the steering wheel.

you XX suspension is bind city

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Well you would have to arrange your lower links, or whatever link you choose to follow with the draglink, so the mount on the axle is in plane with the steering arm on the knuckle, not a huge deal but the most often times the draglink would be inboard of the suspension links, making it hard to get it to go across the suspension link and attache to the steering arm.

As far as the vertical input steering box, why? Just run your steering down like normal, and use a direction changer which bolts to the end of the shaft and has internal gears and has an output below the input facing backwords, this would go into the box. And you can get them so they reverse the rotation direction or stay the same, problem solved.

Actually you haven't seen my XX setup and it does not bind. The links do not cross over each other as much as the XX looks, my computer only has one style of X's so I couldn't make it look like mine /forums/images/graemlins/rotfl.gif

The problem with a 4-link is that it tries to twist the axle when flexing (or deflect the links...i.e. poly bushings). Think of it this way:
The IC in the side view is what the axle would be rotating around at that instant (by definition).
Now just think about one side. As you lift the wheel the axle will gain positive caster (lean backwards). As you lower the wheel it will gain negative caster (lean forward).
Now think about the other side as well. When one wheel lifts it will gain positive caster...as the other wheel drops it will gain negative caster. The diferance between those angles is how much you are trying to twist the axle housing! Now we are talking about a 3.5" diameter sway-bar!

There are a few ways to get around this.
1) Make the links parallel to each other and the same length (so that they stay parallel). This is how Dodge Ram trucks are as well as Jeep Cherokee's. You will have no change in caster and so no attempted twisting of the axle.
2) Use link ends that can deflect. This is the way a Ford radius arm suspension works. They have rubber bushings at the frame end and a huge bushing around the axle housing. If you install longer radius arms you will have less caster change on each side and it will flex better.
3) Use wristed radius arms. This is where you are able to unhook one of the "y" links when you wheel it (or just build it with one "y" link and one straight link). All this really is is a 3 link with the 3rd link all the way over to one wheel (often on the side where the driveshaft is to keep it happy). When you have body roll you will get different caster depending on which way you turn. That might be fun in a NASCAR but not when you have to turn both directions. Most people wouldn't notice it (just like audio stuff) but I would. You also have problems with torque lean on breaking and accelreation (which I haven't even wanted to calculate out yet...too messy).
4) Use a 3-link or leaf springs.

Or wrist the front axle, problem solved /forums/images/graemlins/grin.gif

That was option 3 /forums/images/graemlins/deal.gif

Uh, no you said wristed radius arms. I'm saying wristed axle. Cut the long tube in half and create a pivot point riding on bearings. So the long tube can rotoate independently of the short tube and diff housing. /forums/images/graemlins/deal.gif

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with a Panhard bar the RC is where the bar crosses the centerline of the truck

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I disagree w/ this... for limited suspension range (like a car) this could hold true, but in the extremes of travel and articulation, I believe the RC actually floats from one end of the track bar to the other....

But as far as the practical side of where to install a trackbar, my advise to you Greg is to keep in mind that the trackbar mounts can be subjected to huge forces.... especially on a steering axle, so part of your decision of where to mount it might be tied to where you have room to build some beefy mounts that aren't gonna give up the ghost..! I experimented w/ about 4 different mounting setups for the front of mine before I finally ended up w/ one that worked w/ minimal bumpsteer.

Marv

This is great stuff!......many of you will be receiving followup questions once I get through all this new content. /forums/images/graemlins/grin.gif


Jason, you may have solved one set of problems with a "wristed axle", but I wonder what the "toe change" might be with a setup like that???? /forums/images/graemlins/eek.gif Sure seems like your tierod is going to be twisting in some weird ways as the steering knuckles go in opposite directions!!!

More questions and comments are on their way.....everyone please continue to "play nice" until I get back! /forums/images/graemlins/smile.gif

It's actually not bad. I saw it in action on a dana 44 front and the twist between the two knuckles was very very small... But the pivot allows all the tension to be taken out. I think the knuckles moved maybe 1"? The TRE's easily took it up and the toe change wouldn't be noticable. There were also stops on the pivot so it could only go so far.

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The ideal setup if I were doing it with mechanical steering would be to do a "wishbone" style setup with the steering box being under the cab with a link running to a idler on the axle so that the drag link from pitman to idler is parallel with your lower 3 link bar and has the same pivot poins, then a short draglink from idler to steering arm. It would be complicated but you would have no bump steer as well as hardly any compression/droop steering since the steering arms always stay the same length in relation to axle position.


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the idler on the axle would be the ds steering knuckle, end of complication.
just please point to the source of a modern, available, sized to our application, steering box with a near vertical input for the steering wheel.

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With the stock box in the stock-ish location.
A intermediate drag-link from the pit-man arm, backwards to an Idler arm, located by/under the cab.
Pair off the idler-arm with the main drag-link that runs parallel to the suspension link, to the Driver's steering knuckle.
From the side, the draglinks would look like a "V" flopped over, on it's side.

Is that what you had inmind ?



No one likes the Watt-linkage idea ?
Why is that ?

And that has all the bad effects as a wristed radius arm and none of the good ones (cheep and easy).

Edit:
I take that back...the only drawback it would have would be complexity and cost. Not all together a bad idea if used with the right type of links but I can think of alot of other things I would rather spend my money on.
/Edit

B C Bronco's Wristed Housing Page (http://www.bcbroncos.com/frontsusp1.html) A freind has this set up on his EB. He likes it.

On the subject of steering, using Jason's suggestions, how about using the stock steering box, driver's side arm on the kingpin, and a idler system? It would be a longer version of the stock system if you could get the idler computed correctly. /forums/images/graemlins/thinking.gif

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The WAH leaves both radius arms firnly in control of braking and acceleration torque, resulting in better on-road manners than either a wristed arm or lengthened radius arms.

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This is the only part that isn't really correct. The radius arms will share the breaking but all the acceleration forces will go through the short side radius arm. Depending on the side that is you might be able to get rid of all torque lean except for engine breaking.

x

x

I wish I had another frame to play with /forums/images/graemlins/tongue.gif /forums/images/graemlins/deal.gif

OK,

Here are my followup photos and questions:


Jason,

Your comments about the axle offset with BOTH sides drooped intrigued me:

http://www.norcalbigdawgs.net/Gallery/albums/albun65/Bad_Offset_doubledroop.jpg

Pretty bad, eh?

Here's a top view showing not only the obvious axle shifting, but also the axle "steer" effect:

http://www.norcalbigdawgs.net/Gallery/albums/albun65/Axlesteer_and_offset.jpg

I got the terms messed up on "anti-squat" vs. "anti dive" obviously anti-dive is the front axle term. Mainly, I was looking for validation that less link angularity up front gives a more desireable "anti-dive" characteristic...?

CG - Boy, I wouldn't mind some help on that one! Even when you have a completely assembled vehicle, the methods for getting this value are difficult to perform (to say the least!) If you (or anyone else) have any ballpark values for what to use for initial calcs.....I'm all /forums/images/graemlins/ears.gif


Donovan & mj:

You both suggested themes of parallel links. Here's a shot of what I tried this afternoon:

http://www.norcalbigdawgs.net/Gallery/albums/albun65/Parallel_and_Outboard_links.jpg

That particular setup uses a 6" raised block off the axletube and attempts to make the link parallel to the ground, as well as parallel to each other...

Here's a top view of that same link arrangement:

http://www.norcalbigdawgs.net/Gallery/albums/albun65/Outboard_links_top_view.jpg

The frame tapers inwards so the links "appear" to be non-parallel, but they are actually pretty close... roughly 36" apart at both ends, and the links are about 32" long... (had to shorten them slightly from the previous setup) /forums/images/graemlins/thinking.gif I'd have liked to make them longer, but came up with some interferences on the rear mount point.


mj:

You mentioned using the existing 2 links as "uppers" instead of lowers (as I had planned)...solves my problem of how to keep the upper (single) link from hitting the oilpan though... It does create a lower link that is likely to get "bashed" on rocks, but then....the original design put TWO links down low...so maybe I just need to revise my thinking?

I am still fascinated by the description of how the idler arm steering could be set up. I can't say that I understand your description fully yet. From the sounds of it, I'd be better off using a stock 4WD steering box (front to back) instead of the current AGR (crossover steering "side to side" style) I currently have. The pitman arm creates a front-to-back motion which is carried back (presumably parallel to the framerail?) to the idler arm....it them transfers those steering inputs BACK towards the DS steering knuckle??? If so, I'm a bit confused how the front-to-back motion is translated into the existing steering arm (which is expecting side-to-side inputs). Do you happen to have a sketch of this idea, or a photo of a truck using a similar setup? I'm curious to see it applied and how it relates to the 3-link geometrically... /forums/images/graemlins/smile.gif


To everyone else:

Your inputs are great! I appreciate the encouragement and insights.....please keep them flowing! /forums/images/graemlins/thumb.gif /forums/images/graemlins/thinking.gif

The second photo shows what I was talking about perfectly. As the suspension goes thru its travel the axle will steer if the links are tapered. Does it now steer with the links being parallel?

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The second photo shows what I was talking about perfectly. As the suspension goes thru its travel the axle will steer if the links are tapered. Does it now steer with the links being parallel?

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Donovan,

What's interesting too....study the links in that top view (near my sneaker!) and the PS link is almost straight forward, and the DS link is obviously angled. I attributed this to the short panhard bar....not so much to the fact that the links were 'tapered' but I'm still learning!!!

As for the "new" parallel links setup. I didn't get a panhard bar setup for it yet. One of the things I didn't mention is that the setup as pictured only has about 2" of bumptravel before it collides with the old bumsptop hangers! /forums/images/graemlins/blush.gif Not a big deal, I will remove them anyway....just didn't feel like grinding rivets tonight (I think I've ground-out about 100 rivets so far....it's becoming quite irritating!) After I get that clearance, the upper shock tabs will interfere too.....(more rivets! /forums/images/graemlins/mad.gif) but after that....I should be able to get the articulation pics....and get a new panhard bar fitted.

I'm still confused by the whole idler-arm thing...I thought (perhaps mistakenly) that somehow a Watson-like setup might take the place of a conventional panhard bar (with two fixed endpoints) and allow one end to rotate....potentially cancelling out the shifting-axle phenomenon that occurs with every panhard bar design.....? Guess I was wrong on that one.

I have also been thinking about coils in the front. However, I don't know if I would like coils with a seperat shock or coilovers. A couple things to ponder: /forums/images/graemlins/wink.gif

Coils and coilovers potentially have different behaviours....this is something I just recently learned. The "key" difference is that the coilovers typically have no provision to "retain" the spring when the suspension unloads...this means that there is no spring rate up front and the front end will feel "light" and uncontrolled. By comparison, a coil spring (and seperate shock) will typically be clamped to it's baseplate and upperplate so there is a "spring rate" acting even under droop, or on a steep climb. This would seem to give better handling characteristics than a standard coilover.

All that being said, I wonder what would happen if someone designed a "coil retainer" for a coilover shock?

My reason for going coils in the front would be to make the frontend more roadworthy. It rides like a brick! I think you could make some kind of bracket that attaches where the factory bumpstop is and then build a bracket onto the axle tube and stick a coil in there. However, you would need to find a coil that is rated for our particular trucks and is long enough to provide the ride height wanted. Then keep the single shock per side up front and maybe accomplish something like the Heeps are running.

Thoughts?

A longer panhard would help but you will always have some axle steer with bottom links that are tapered and a panhard.

x

[ QUOTE ]
A few things to point out...

The side-to-side movement during articulation is due to the placement of the roll center (with a Panhard bar the RC is where the bar crosses the centerline of the truck). You just have to think about it the opposite way as you would with the body rolling and the axle staying flat. If the Panhard were at axle level (or the RC in general) the axle would not move side to side while articulating. If you had the Panhard/RC below the axle the centerline of the axle would move the opposite way that it did in your pic's.

To throw another wrench into the machinery the placement of the RC will affect tire clearance!

If you lower both ends of the Panhard you will be able to stuff a longer bar in there and get rid of some of the side to side movement under 2 wheel bump/droop that Borrego was talking about. That might even improve your tire clearance but will give you more body roll (which might mean a sway-bar up front...another tube to add to the farm). Bump steer wise you want to keep the Drag-link and Panhard the same length and angle.


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Dan,

Here's the ugliness I'm imagining with your suggestion of a lowered panhard bar.....

http://www.norcalbigdawgs.net/Gallery/albums/albun65/12inch_drop_PHD.jpg


Since there's 12" inches between the lower framerail and the top of the axletube....that means that the "drop" of the PHB needs to be 12 inches!!!

Forgetting about the steering forces, and the reduculous amount of bracing it would take to make that actually survive.....I don't like the looks of it from a ground clearance perspective when the DS tire stuffs!!! That PHB is hanging WAY below the axle, and seems to be just begging to be torn off by a rock or treestump....????

Anyway, I need some kind of PHB solution.....but I'm not sure this "pure" solution will work very well in real life. /forums/images/graemlins/1zhelp.gif

Wow, this is an interesting discussion to put it mildly.

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mj,

Pardon my crude MS Paint artistry..... but is this the concept you are describing for the idler arm???



http://www.norcalbigdawgs.net/Gallery/albums/albun65/idler_arm_steering.jpg



I tried to illustrate the steering link (the 2nd link in the steering system) as being parallel with the lower suspension link.....

Looks like an interesting "next" project for me to play with, and also makes useless all the highsteer and crossover components I've just recently acquired... /forums/images/graemlins/tongue.gif




ps. You think "I" am doing YOUR homework? HA!!... without your input, my own work would be seriously stalled.... /forums/images/graemlins/thinking.gif

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MJ
I wish I could remember where it was but I have seen a "show truck" that had almost the same steering you are describing.

It had a link setup with the links in front of the axle. They than moved the steering box all the way to the front and used a push pull setup. Not what I would do but interisting to look at.

Greg
I wouldn't drop the PHB down 12"...that seems alot to me as well. However if you dropped it a bit more than 6" you might be able to fit it under the frame. You might also get away with angling it down just a bit and making a compromise that way. I just don't see you being happy with that much side to side movement under 2 wheel bump/droop. The only way to solve that is to make the PHB longer or not use one at all. I also don't think you will have to worry that much about bump travel because the tires will hit the sheet metal and be your limiting factor. MJ and I differ some on where your roll center should be. You are in a better spot than most doing the front end first because I think you should have the RC higher in the front than in the rear. When you don the rear first (and still have leaves up front with a RC at about the axle centerline) I don't think you should move the rear RC up at all. Starting at the front (the heaver end!) you don't run into that problem and could be free to raise the front RC some.

Either way you need to attach the PHB mount to both frame rails! It will have alot of load going through it.

Edit:
The only approximation I have heard for unsprung CG is motor camshaft height.

If you are going to have a draglink that crosses the chassis centerline then you are going to either have one hell of a lot of bumpsteer or you are going to have lateral axle dislocation. End of that part of the discussion.
If you don't want the lateral dislocation then you will have to move the steering box to a location where the draglink can follow the suspension's control arms down to the axle. So picture the stock 4x4 draglink's location, only now move the box back on the frame to where the linkage arms connect to it.
Here is the kicker though, If you go with a 4 link then the axle end postion will be some ratio of the distance btwn the axle mounts. The frame end of the draglink needs to be located at the same ratio btwn the frame ends AND it also needs to be a length that is a ratio of the linkage arm lengths.

The amount of 'steering' the linkage induces in articulation is directly equal to the angle of the Roll Axis. The flatter the Roll Axis is, the less 'steering' there will be.

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Uh, no you said wristed radius arms. I'm saying wristed axle. Cut the long tube in half and create a pivot point riding on bearings. So the long tube can rotoate independently of the short tube and diff housing. /forums/images/graemlins/deal.gif

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You mean one of these. (http://www.bcbroncos.com/frontsusp1.html) Gary Yorst up in B.C. was the first I know of to do that, about 8 years ago.


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No one likes the Watt-linkage idea ?
Why is that ?

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Simply put, the Watts linkage depends on the length of the horizontal locator bars and the rocker arm's length to define a decently long near verticle path. Once you exceed those travel limits the axle's travel path diverges from linear rather radically. For the travel path distance most are looking for in off roading of any nature it is very hard to make those parts long enough. Matkins, as an option on their frames, laid the Watts Linkage over to be all in the horizontal plane rather than the more common verticle plane. I haven't heard nor seen much about this so it may have been a flop. I would expect it to be since the axle is now, presumably, traveling nearly verticle while the draglink is still traveling in arc. Instant bumpsteer.

CG fore/aft location usually tends to be at the flywheel surface. Either Cam CL or Crank CL can be used for approx CG height.

Finding it on a complete vehicle isn't all that hard. A little laborious and requires some simple Trig, but no that hard.

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I am trying to follow you here Donovan,

you are going to get 'some' roll/axle steer with the links being perfectly parallel, unless both sides move the exact same amount.
does that ever happen in the real world?
one side compresses exactly the same amount the other extends?
I think i see that, even if it isnt exact mirrored motion one side will cancel the other rather then angled ones that would compound the difference until they hit the parallel point.

the desire to use very large tires and maintain some semblance of a vehicle, and maintaining as much break over as possible would preclude me from using links parallel to terra firma.

on the other hand as flat as I could get within the compromises would be high priority.
more because I dont like the look of steeply angled control arms,
as it looks as though they are as likely to tuck/bow under the rig on a hard impact against something 1/2 the hieght of the tire as go over.

no reply neccesary but appreciate one if I am completely lost and missed your point.

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Yes this does happen in the real world. Just drive down the highway and this happen. Yes you will get roll steer but it will be at its max articulation not during normal driving. I assume that this in the reason to build the link front suspension is to make it drive to the trail and not scare the sh!t out of you.

Here is my dumb ? for the day. Why not just design it off a factory set up like a Jeep TJ or an older Bronco? It seems to me it would be easier to somewhat copy a long arm Jeep design then go through what you are doing. With that said, I know absolutly nothing on what you are planning to accomplish but I thought it was logical. /forums/images/graemlins/ignore.gif

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Here is my dumb ? for the day. Why not just design it off a factory set up like a Jeep TJ or an older Bronco? It seems to me it would be easier to somewhat copy a long arm Jeep design then go through what you are doing. With that said, I know absolutly nothing on what you are planning to accomplish but I thought it was logical. /forums/images/graemlins/ignore.gif

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That's what I was thinking. Find coils that can hold the weight of our trucks and thelift height wanted and then build a couple of brackets and link bars.

My question. Can you still put shocks in the stock locations or would you have to relocate them so they stand straight up with the coils?

the reason i see for not doing it this way is because the stock jeep or dodge coil suspension is meant for road driving first, then a bit of trail stuff. the maners in how it handles and rides is bass akwards.
Grant

Early Bronco frontend:
http://coloradok5.com/photos/data/500/1736front_end_line_art.jpg

For a daily driver that wants a better ride in the front, why wouldn't something like this work? I think figuring out where to mount the radius arms and designing a track bar would be the hardest parts.