TOTW: Three link suspension

34014 Views 58 Replies 25 Participants Last post by ChrisPy, Mar 6, 2003

Mo

Discussion Starter · Feb 18, 2003

Welcome to the next installment of the

Topic of the Week

This time, we're going to discuss the three link suspension.

Please try to keep discussion of the 4 link suspension to a minimum, as that will be the next topic for discussion.

Discuss amongst yourselves.

1 - 20 of 59 Posts

LAME

· #2 · Feb 18, 2003

All I'm gonna say is if you are gonna do a 3-link, you must understand how and how much you are loading the ends. Disco axles aren't as cool as it may seem. IMO you have a bit more room for fawk ups with 4-links...but thats for next time

IndyCJ

· #3 · Feb 18, 2003

Uh, newbie question :flipoff2: or perhaps to get the ball rolling

When, where, and why would you use a three link?

Ghetto Fab.

· #4 · Feb 19, 2003

Seems to me, and feel free to flame away, that people have gotten 3 links somewhat confused with 4 links. A lot of people seem to consider having to lower links plus an upper wishbone or A-frame as a 3 link, since there are 3 main parts. Whereas a true 3 link is simply two lower links and one upper LINK. Each link having only two connection points. Side to side axle location is done via a panhard rod or track bar.

The wishbone or A frame suspension geometry acts just like that of a triangulated 4 link the only difference being forces on the joints.

Anyhow, just hopeing to clarify what were talking about!

Kevo

Azzy2000

· #5 · Feb 19, 2003

Ghetto Fab. said:
Seems to me, and feel free to flame away, that people have gotten 3 links somewhat confused with 4 links. A lot of people seem to consider having to lower links plus an upper wishbone or A-frame as a 3 link, since there are 3 main parts. Whereas a true 3 link is simply two lower links and one upper LINK. Each link having only two connection points. Side to side axle location is done via a panhard rod or track bar.

The wishbone or A frame suspension geometry acts just like that of a triangulated 4 link the only difference being forces on the joints.

Anyhow, just hopeing to clarify what were talking about!

Kevo

Seems like a lot of hot rodders like to rule out the panhard as not being a link.. they tend to call a 5 link a 4 link and a 4 link a 3 link... i call a wishbone 3 link with one upper arm a 3 link... cuz its got (duh!) 3 links and so on and so forth... :flipoff2: but anyways....

cmk

· #6 · Feb 19, 2003

There's one problem here; in terms of geometry and dynamics, a "3 link" must be modeled as a 4 link.

Afterall, a 3 link is nothing more than a 4 link with 2 links converging before they meet discrete mounting points.

cmk

LAME

· #7 · Feb 19, 2003

cmk said:
There's one problem here; in terms of geometry and dynamics, a "3 link" must be modeled as a 4 link.

Afterall, a 3 link is nothing more than a 4 link with 2 links converging before they meet discrete mounting points.

cmk

Yep. Thats why I think you have less tolerance in fawking up link loads.

Once again, material does not make up for poor use or design.

Ghetto Fab.

· #8 · Feb 19, 2003

So would a 3 link (non A-frame upper), located with a watts linkage be a 5 link?

Since the A-frame style 3 link acts like a triangulated 4 link, thats the category I put it into. Besides its an A-frame not a link.:flipoff2:

I haven't fully researched the panhard rod geometry, but from what I have seen it is different from the A frame and triangulated setup. Can someone explain if this is or is not true?

My point, and this is probably really dumb, is that these two different styles are often called the same thing. When discussing them it needs to somehow be clarified what we are talking about so that we may all be on the same page. Doesn't really matter what you call it as long as we know what it is.

Kevo

Azzy2000

· #9 · Feb 19, 2003

cmk said:
There's one problem here; in terms of geometry and dynamics, a "3 link" must be modeled as a 4 link.

Afterall, a 3 link is nothing more than a 4 link with 2 links converging before they meet discrete mounting points.

cmk

...and theyre welded together to form ONE link... with one attachment at one end and two at the other.. i like simple math, im not an engineer.. a 3 link is a 3 link is a...NOT 4 link
:flipoff2:

LAME

· #10 · Feb 19, 2003

Azzy2000 said:
...and theyre welded together to form ONE link... with one attachment at one end and two at the other.. i like simple math, im not an engineer.. a 3 link is a 3 link is a...NOT 4 link
:flipoff2:

Do the layout. Convergence points are gonna be similar between the turkey bone and a real 4 link. Recall cm"link bitch"k was talking about dynamics and geometry.

Azzy2000

· #11 · Feb 19, 2003

LAME said:
Do the layout. Convergence points are gonna be similar between the turkey bone and a real 4 link. Recall cm"link bitch"k was talking about dynamics and geometry.

I understand what youre saying and where youre coming from but this is a pointless debate... im just saying if its got 3 links, im gonna call it a 3 link for sure...

chadl

· #12 · Feb 19, 2003

Isn't the 3-link that MO is getting at 2 radius arms and a panhard bar. Such as the front end of a full size Bronco, or some of the aftermarket TJ kits?

I'll toss this out there, and try and get everyone on the same page, (even if it's the wrong one) :flipoff2:

1 5-link (4 individual links, usually not parallel with panhard bar standard TJ setup)
2 4-link (4 links, trangulated to control lateral movement)
3 3-link (like 2, but the two triangulated links come together prior to attaching to the axle, like the rear of my wife's liberty
4 3-link (radius arms and a panhard bar ford bronco style)

If I'm wrong on these tell me and I'll edit it, but at least all discuss the same things.

Chad

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IndyCJ

· #13 · Feb 19, 2003

Ok, time to start drawing. Fire up paint, and let's see some pics of what everyone thinks is a 'three link'.

And to fuel the debate, is the definition of a three link based on where it's attached at the axle? Or the 'other ends' of the links. (ie, the 'wishbone' actually has 4 attachment points to the 'frame', but only 3 to the axle?)

Thoughts?

ccj8008

· #14 · Feb 19, 2003

Try this link:

http://www.jeepaholics.com/tech/quarterellip/

Seems a key point is to angle the lower links inward to prevent rear axle flex steer.

cmk

· #15 · Feb 19, 2003

Pardon my lack of detail in my first post.

The 3 link suspension configuration I was speaking of is the wishbone type "3 link." That configuration of links is modeled identical to a 4 link because there are in essence 4 links. The number is commonly (and incorrectly) reduced to 3 because the uneducated only "see" 3 physical links.

There is another type of 3 link, a true 3 link, and that is the radius arm plus panhard bar setup that some have brought up. That style of suspension uses a completely different methodology to determine its performance compared to a 4 link.

Speaking to 5 link suspensions such as a stock TJ, there are some nuances in that design because there is a redundant link. Ideally, that style of suspension should be reduced to 4 links (3 latitude and one panhard), but for other reasons (safety, cost, etc) it is not.

cmk

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IndyCJ

· #16 · Feb 19, 2003

Ok,

So where would one start to build a three link suspension?

LAME

· #17 · Feb 19, 2003

IndyCJ said:
Ok,

So where would one start to build a three link suspension?

On a rig, in the garage.:flipoff2:

What do you mean? First step in designing the suspension?

IndyCJ

· #18 · Feb 19, 2003 (Edited)

LAME said:
On a rig, in the garage.:flipoff2:

What do you mean? First step in designing the suspension?

Bah! Smartass. :flipoff2:

Yea, first step in designing. What to measure? Where to measure? What factors you need to take into consideration when you measure? Etc.

How 'bout a group project? :flipoff2: I've got my rig setting in the garage (project, not yet complete) and say I want to do a 3 link rear for it. You tell me where to start, and I'll start measuring, and we'll design it 'online'. I'll take some pics, some measurements, and let you Jethro's start your gazinta's.

JEEP_TJ_FREAK

· #19 · Feb 19, 2003

From the design standpoint I would run the same mounting points with either a 3 link or 4 link just the wishbone 3 link having a centered mount as opposed to a triangulated 4 links slightly spread mounts. The vertical positioning as opposed to the COG would be the same, the effective length of the links would also remin the same.

The most common issue people have with mysetup is the way I have the damn center mount oriented.

Here is a pic.

Okay yes it is true that that bushing is not mounted in a manner to accept a massive amount of sideloading, I am not argueing that. If you want to build a wishbone 3 link with parallel lower arms (or vise versa) you want the mounting bolt for the bushing to be rotated by 90*. This is not an issue for setups like mine where the LCAs are triangulated more severly then most TJ people have on their uppers and can run no track bar. If the those setups work without excessive lateral movement then I don't see why much force would be applied to the side of that joint. It seems very obvious to me but many cannot grasp this concept, lateral forces on that joint are transfered into a push/pull rather then sideload when the LCAs are triangulated.

Parallel links suck ass! If you can do without them do it. Just look at a bone stock TJ, theirs are not parallel either. They are not as triangulated as mine but far from parallel too.

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LAME

· #20 · Feb 19, 2003

IndyCJ said:
Bah! Smartass. :flipoff2:

Yea, first step in designing. What to measure? Where to measure? What factors you need to take into consideration when you measure? Etc.

How 'bout a group project? :flipoff2: I've got my rig setting in the garage (project, not yet complete) and say I want to do a 3 link rear for it. You tell me where to start, and I'll start measuring, and we'll design it 'online'. I'll take some pics, some measurements, and let you Jethro's start your gazinta's.

I would say t-case to rear axle. Figure out where you can mount the links to the frame.

Get pics, and measure everything, then online hack fab can start

1 - 20 of 59 Posts

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