Lower Links 101

[NorCal_Prerunner]

It would be sweet if every month or so, there could be some kind of technical thread on building a piece or part of a desert truck from start to finish. I was hoping to cover building lower links for a 3 or 4 link setup. I always see plenty of great parts completely finished, Bent, Boxed, TIG welded, Dimple Died, ect, but never get to see the full make-up of a part from start to finish.

1. You determine you actually need or want a 4-link setup on your truck.
2. You have the tools, fabrication skills, and aren't a complete dumb ass.
3. You don't have access to a mechanical engineering program such as Solid Works to design it.
4. Where do you start?

A: What materials are you going to use? Tubing type, diameter, thicknes? Plate type, thickness? Heim size, threaded insert? Bushing type for front pivot? Cool, all that crap out of the way.

B: How to determine the lenght of the lower link?

C: Things to consider when designing the lower link?

D: Some images of expoded views of different lower link designs. (Kris loves to post, so let's see an exploded view of one of the lower links he has designed)

There is so much more that goes into a 3 or 4 link setup than building lower links. Everything could not be covered in an organized fashion in one post. I hope this post provides educational info for some of us.

Looking for posts from people have successfully designed and built a 3 or 4link setup that worked well.

What do you think. And no, 1,2, and 3 are NOT describing me, I just thought it would be an interesting and informative post. Later, J_





It's never too late to be what you might have been....

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[Kritter]

No lower links my man..sorry. Havent had the want (read, money) to take the time and design one...yet. V8Ranger might have some of his SW drawings or I know John Richer has some.

Kris
"Buy American before it's too late..."

[1992f150]

no one in the bussiness wants to give away their secrets.

Azusa: shame of the foothills

[Curtis Guise]

I think that is a good idea. And starting with a 3 or 4 link setup sounds good to me since I plan to start building one soon. I have some ideas from looking at other trucks but to know how to get the correct geometry and materials to use would be great. (from people that know what they are talking about)

If enough people would contribute to this idea then maybe Klaus could start a new topic on the board called "projects" or something like that.

[ntsqd]

Some of the things that need consideration in a rear linkage design:

Roll Center Progression (where it is relative to the axle at any point in the travel)

Roll Axis Inclination (To avoid or minimize 'Rear Steer' when the axle is twisted relative to the chassis)

Instant Center Location (Anti-Squat/Anti-Rise Properties)

Pinion Angle Delta (How much and in what direction the pinion angle changes from bump to droop)

Wheelbase Delta (How much the wheelbase changes from full bump to full droop)

Those are just off the bottom of my head. Everyone will assign their own priorities to these, and what ever others I missed. Where's Bob ?

Perhaps we ought to start a new thread ?



TS

I used swerve around my halucinations, now I drive right thru them.

[NorCal_Prerunner]

Looks like TS has most of the things to consider when building a lower link covered. So now let's some basics covered such as A, B, and D. I don't want this post to get hyjacked with buckets of super tech info yet. Let's just get the basics covered first. Remember this post is NOT how to completely build a 4-link, just a part of it. All of TS's comments are very important. In due time though. Although this is a complex task, we are not talking about a designing and building a new type of micro-processor for a main logic board, so I don't understand the trade secret comment. We're talking about a fawking lower link. Good information for everyone.

It's never too late to be what you might have been....

[CRAIG_HALL]

One thing I tend to see alot even on some fairly nice trucks is the coilover & bypass mounts being above the centerline of the front and rear pivots. This makes the arm rely on the front, which is usually a bushing to keep it straight,prematurely wearing out the bushing. the mounts should be below the centerline allowing the arm to stay vertical and not wear your shock heims or your expensive delrin bushing or that 95.00 rear heim, usually I see 1-1/4" heims. Tube arms are simpler than sheet metal ones but you need the vertical strength at the shock mounts so I seem to favor a sheet metal arm possibly out of .090 chromolly if the sides are tall and vertical or maybe 1/8" if you make a triangle and taper the sides up . Try not to leave an open pocket at the shock mounts so that water and dirt collect and rust away your arm. I have some arms drawn but, there on auto cad at work (sheet metal shop) Just some things I've seen on other arms I've only made tube ones Craig

[Curtis Guise]

The only problem is that if you try and answer B (lower link length) then almost everything that Thom brought up will be a factor. Because the length of that one piece has something to do with the rest of the setup. So in my opinion it would make sense to figure out the geometry of the entire setup.

I guess what I am trying to say is that it might be hard to answer B without the thread getting alot of "super tech info". But that's ok with me.

[NorCal_Prerunner]

I'll all for super tech, but let's get the basics out of the way first. I agree with you that B is too hard to answer without addressing a lot of other things. I wish there was a orderly way the board could sort the posts. Thanks for the reply JDfab.

It's never too late to be what you might have been....

[ntsqd]

Somebody measure their truck. It needs to be a representitive truck.
Best way to measure is to use a flat piece of level concrete, a plumb-bob, and some chalk. We need to know:

Center of Gravity: Let's use the common assumption - the crank centerline at the flywheel surface. We need to know how far back it is fron the front axle centerline and we need to know how high off the ground it is.

Wheelbase. Measure it, don't quote what is considered 'common knowledge.'

Eventually we'll need to know where the frame rail is, but those two numbers will get this going.



TS

I used swerve around my halucinations, now I drive right thru them.