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Design, geometry and functionality of tracbar-less suspension

Beezil,

Then your looking at a triangled 3 link or a triangled 4 link. Your big questions are are you going to coilovers? Single sided Hydro steering or double sided hydro steering. The coilovers will give you more room for arm locations.

I still like the inverted triangled 3 link design Ron has for keeping all the need clearances. I will eliminate your TB. The triangled lower keeps it out of the way of eveything on your jeep.

mark
orgs mfg
 
I highly doubt this is a good system, but teraflex came out with a bolt on trangulated front 4-link for TJ to get rid of the tracbar. It looks a bit junky to me especially being bolt on, but there was a review in JP magazine on it. They said it wasn't all that bad, but they NEVER give bad reviews. I guess you could take a look at that and maybe get a small idea or two to help you design yours. _nicko_
 
People have pretty much hit on the issues and you seem to already be aware of them yourself, but I'll chime in for the "hey".

If you don't run a track bar/pan hard/lateral tracking bar; you will have big steering challenges so long as you maintain a drag link tie to the steering box.
As the suspension cycles, the drag link will push and pull the steering knuckle along the arc of the drag link. Unless the axle itself is moving along the same arc, the wheels will be forced to turn as the suspension cycles; ie bump steer, etc. This is the reason why the pan hard arc must match the drag link arc.

If you go full hydraulic and do away with the drag link, you do away with this problem but you do introduce some other problems with full hydraulic; namely, a very "wiggy" driving feeling at speed. 60 mph in a full hydraulic requires more than a little attention.

Second isssue can be clearing the oil pan. You should be able to design around it but it's an obstacle none the less.

IMO, a well designed pan hard link system (however many link points you want to count it as) is a very sound and predictable suspension system for front axles.

You can do it, but I'm not sure you'll neccessarily see any beneift of it over a well designed panhard link system.

If you do go w/o a panhard up front, I might recomend a wishbone style. I believe that the wishbone can offer superior lateral rigidity over a four link and also crazy travel.
You could also consider a forward mounted wishbone which would avoid the oil pan clearance issues.

Walker Evans ran this type of setup on the front of his 2001/2002 S10 Compeition truck.:)
 
Beezil- You really need to quit crawling around in my head. I've been working on the design of a front four link for my junk as well. As you know the front is very limited for space, and the final product will be all about compromises, especially if you don't want a "U" design like Sean and Matt. Here is a pic of what I"ve come up with. Warning: No fancy CAD drawings here, but I'm fluent in low tech.

site1044.JPG


The upper link will BARELY clear the pan with uptravel limited to ~4-5". Obviously I still have to work out the bugs, but at least I now have a starting point. I've got a PVC axle and control arms made, so I can cycle and change things without busting a nut.

-Jon
 
c-rok

this is a rig that will never see the more than 20 mph......bumpsteer is not an issue, even if I decide to run a sag box style steering, the effects of draglink operating in an arc while the axle cycles vertically is not a concern. My main concern is to not have the axle operating in an arc. THATS THE MAIN POINT. On my existing setup, my short tracbar is the problem. but your points are well taken.

Kacz.....

hold it right there mister! don't go anywhere.......Can you please comment on how you've located your roll center, and how you are organizing the points of rotation on all your links to give you what you are looking for in anti-squat and anti dive? I cannot tell from your drawing if you are locating the U-arm on the lower or upper side of the axle? also, it looks like your u-arm is positioned a little foreward of the axle tube, or is this just an extended construction line?
 
Sure sounds like a dry sump system would solve a lot of problems :D Have you read Chassis Engineering by Herb Adams? Great book, goes into explicit detail about much of what you are talking about. I have thought about doing the same, but time and budget don't really allow such severe modifications. Hope you find a system that works very well, and keep us updated (like you always do). Hope Matt chimes in soon. He should have some good information.
 
Beezil- The "U" arm mounts will actually be approximately flush with the rear of the axle tube. The extended construction lines are only to aid with the geometry layout (if you look closely, you can make out the points flush with the tube). The uppers will have ~5" horizontal seperation and be ~6" above the tube centerline. The lowers will be just below the centerline. The pictured drawing is only a rough lay out of "what fits", primarily around the oil pan and frame design. I have yet to actually do the work of calculating the roll axis and anti-dive of what's pictured, but by my scientific "eye-ball" method, the roll axis seems to be a bit steeper than I'd like. I plan on moving the LCA frame mounts lower than pictured to get it better. I'd like to move the uppers up a little, but I doubt there will be room.


Keep in mind, I'm just beginning to understand front 4 link geometry. I have a grasp of rear (uh-oh, that ain't right) geometry, but I don't yet understand how front and rear roll axis, anti-dive, and anti-squat correlate. More importantly, I don't know how much room the front of the XJ will allow us to change this. It makes a buggy more appealing every day.

-Jon
 
Kacz,

I can dig it.

I have definite plans to build a buggy.

its for sure.

but plan A is to use this free cherokee as a "sketchbook" as well as a test platform to experiment with a couple new suspension designs as well as add new parts while I'm working on driving skill. The whole while I'll be going bigger on the xj until I figure everything out, then I will build the buggy frame while I'm driving an attending events, and when I'm finally ready I'll make a quick switch of the goodies....

sounds like this is kinda what crash and a couple other folks I know are up to, makes sense.....I want to "get it right the first time" when i go to build the buggy.

I don't care so much if I re-work the xj link geometry for the worse......I'm just trying to do something sorta new as a learning experience....

all the responces have helped, including the recommendations on books, to those who have listed titles or authors, thanks. I'll be checking thos out soon.
 
Beezil said:
c-rok

this is a rig that will never see the more than 20 mph......bumpsteer is not an issue, even if I decide to run a sag box style steering, the effects of draglink operating in an arc while the axle cycles vertically is not a concern. My main concern is to not have the axle operating in an arc. THATS THE MAIN POINT. On my existing setup, my short tracbar is the problem. but your points are well taken.
Click to expand...

Careful with the assumption on steering arc. With a long travel the knuckle can pull over far enough that you're left with no steering adjustment; ie the steering is all used up with the arc pull from the drag link. You may have to turn the wheel all the way right to go straight on down travel situations and vice versa on up travel. Just something to consider.

Going full hydraulic is a good thing for a full time Rock Crawler. And it's not that you 'can't' drive it at speed; it's just that you need to be a 'little' more attentive;)

Like I said earlier too; you can use a forward mounted wishbone to avoid the oilpan. Your limited on total vertical travel due to the shorter length allowed of the wishbone but can still have plenty of articulated travel.

Suspension design stuff is fun:D
 
Say you build a link system, triangulated, wishbone, whatever; set up properly so as to contain lateral movement of the front axle. How would the steering issues be any different than say, a front leaf sprung old CJ with crazy flex. I know in my 48 willys, I can score over 1000 on a 30* ramp.( whatever that's worth) with no steering issues.

Am I missing something?
 
How would the steering issues be any different than say, a front leaf sprung old CJ with crazy flex
Click to expand...

exactly dan.

My cj-6 had an awesome amount of flex with front buggy springs and shackle reversal, and steering was never an issue.
 
articulation is all about TWIST unless you have independent suspension, so the drag link would not have to grow or shrink in length with the fulcrum being in the middle of the axle. That's my take on this.


Dan
 
As did my leaf SOA Scrambler and I think you make good points.

The difference is though what point the axle is pivoting around. On a leaf sprung system in articulated travel, it will roughly be pivoting around the compressed leaf spring. On a drivers side drop, this won't matter since the drag link will remain relatively flat. On a passenger side drop the axle will pivot around the drivers side spring perch which is relatively close to the centerline of the steering box, thus no noticeable drop steer effect.

On a center linked system the axle will roughly pivot about the center link points and the drop steer effects will be more noticeable.

If you have enough turning swing on your knuckle you may be able to negate the affects, but it will be there to some degree. It's unavoidable.
 
Maybe the difference is that the tierod and draglink on my willys are just about parallel, unlke the majority of lifted XJs out there.

Maybe a track bar-less system with drop pitman, and high steer knuckles would help negate this phenomenon.

Or maybe it's just a secret obsession to make something in the front end 'parallel.'

Dan
 
Dan/Beezil,

Greg said it right. The Center link setup twists the axle at the center point across the axle. A leaf spring setup is just like a TB setup the axle twists in a large arch starting from the driver side (or high side) the same place the Steering gear is attached. On a center link your steering gear would need to be attached close to the center link as possible. Then you would have a REAL short drag link which creates many more problems, not the least of how to attach a steering gear to the center of the frame.

mark
orgs mfg
 
Then you would have a REAL short drag link which creates many more problems, not the least of how to attach a steering gear to the center of the frame
Click to expand...
You wouldn't need to attach the steering gear in the center, just the attachment point for the draglink.
Put an idler arm on the passenger side and run a relay rod from pitman to idler, attach the draglink in the center. Maybe you could even run one to each wheel separately, kinda like IFS steering.
 
jimk403 said:
You wouldn't need to attach the steering gear in the center, just the attachment point for the draglink.
Put an idler arm on the passenger side and run a relay rod from pitman to idler, attach the draglink in the center. Maybe you could even run one to each wheel separately, kinda like IFS steering.
Click to expand...

Ya..... But I'd just go to full hydraulic before I got myself into a multi-linked steering drag link system.

I'm not disagreeing here. What you described is the same kind of steering geometry that mega lift (mostly street) trucks run. Sometimes called "swing set steering" because of the swing rocker. Like this:
http://www.randyellisdesign.com/FAB PICS AND STUFF/sub7.JPG

While it certainly does work, it is comparitively much more complicated than just two hydraulic hoses, a ram and a tie rod. But I'll grant you that it does solve the drop steer problem.
 
jimk403 said:
You wouldn't need to attach the steering gear in the center, just the attachment point for the draglink.
Put an idler arm on the passenger side and run a relay rod from pitman to idler, attach the draglink in the center. Maybe you could even run one to each wheel separately, kinda like IFS steering.
Click to expand...

I was just trying to give them an idea of what needed to be done so they could picture it in their mind. In no way was I suggesting that as a solution. Full hydro is the only way to go, IMO, with a 3 or 4 link type suspension setup.

mark
orgs mfg
 
I hope you dont mind me asking this question in this thread but here it is.
I have wondered about the effects that kits like RE's control arm drop brackets have. Dropping all the control arm 4" also then lowers the point of convergence of the arms by the same amount. But the rear has not been changed but do not know how this point is worked out this point on on leaves. Is there one?
Now I read in a suspension book the the roll centre of a leaf spring is halfway between the spring perch and the lower shackle eye centre. Would you agree with this and if so the rear roll centre would go up 2" on a 4" lift for example. So if you did a tie rod flip and raised the trackbar mount on the axle by the 1 1/2" -2" to keep it parallel with the drap link would this then help balance what has happen in the rear?
Sorry for all the questions but want to learn more about this;)
 
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