Front 4 Link Modeling

[Kaczman]

Did you just tell me to go SLOW??? The bitch hasn't moved in 12 months. I drew out the original plan months ago, let it settle, and now I'm back to it. My brain was finally starting to return to a solid state.

Daddy wants to do some wheeling next year.

-Jon

 

[Beezil]

kaz.

hurry the fawk up.

trails are closing left and right.

I am rolling parabolas to order.

now is your only chance.

good luck.

 

[Willis]

I am rolling parabolas to order.

now is your only chance.

[hijack]

Seriously? PMed ya...

[/hijack]

 

[Matt S.]

Why hasn't someone done a dry sump? I know they are not that difficult, maybe I am just not thinking through it all. I WILL be doing a dry sump on my project, but not to make room for links. Should we start another thread for this??

MATT

 

[Kaczman]

Version 2.0

Lets see if this looks a little better. I moved the LCA mounts to 1" above centerline with 38" horizontal sereration at the axle and 26" at the frame. The UCAs have been moved to the where the stock LCAs mount.

The roll center is flush with the front of the axle tube, and roll axis is around 6 deg.

Now if I can get the pic to show...

Any input?

-Jon

 

[JnJ]

Picture isn't working.

 

[MaXJohnson]

"The roll center is flush with the front of the axle tube, and roll axis is around 6 deg.

Note: Roll center is always at the axle vertical centerline.

So, you don't want to narrow the lower arm mounts at the chassis? Making the upper arms shorter will increase pinion gain, but I'm only talking 1" - 2". Just enough to get the link in front of the frame rail to spread out the arms. You can compensate for this by lowering the chassis mount of the upper arms a slight amount and by taking some length off the lower arms. You can also point the pinion a few degrees on the high side at static height. No guarantees that this is workable, just some suggestions.

 

[Kaczman]

Note: Roll center is always at the axle vertical centerline.

OK. I misunderstood and thought the R.C. was defined by the convergance of the upper links.

So, you don't want to narrow the lower arm mounts at the chassis?

In the current design, they are inboard 4". I may run into the d-shaft if I take them in anymore.

I tried lowering and widening the UCAs at the frame, and it fits much better than I anticipated. It also gives me a little more room at the oil pan. The LCAs have been moved up on the tube, which will help with the roll axis as well.


Now, lets see if I can actually get some pics to show.

I can see the pics, can anyone else?

-Jon

 

[Beezil]

i think it would be extremely helpful for you to slide your axle under there (if possible) and model the links so you can see where the pinion and driveshaft problems are.

the oil pan is only ONE aspect of the whole problem.

also, the lengths of your arms are very different. have you determined pinion changes during suspension cycling?

also, and i haven't worked this out, this is sort of a knee-jerk reaction....... but how bout bind?

because those link lengths will create some amount of pinion change, the worry would be, what forces are at work between the drivers side, and the passenger side when the axle is articulated?

its kind of the same thing to think about on radius arm designs that use two link mounting points at the frame and four on the axle....

 

[Kaczman]

Binding is a big concern right now. Everything "fits" the way it sits now, but I need to tack in some frame mounts in order to cycle the suspension. It is almost impossibe to see how the entire package will work without fixed mounts at both ends.

As for the pinion, I should be able to shorten the lowers (~4") to get the pinion to rise with diver's drop. Uppers would be 26" and the lowers 28".

Keep the critiques comming.

-Jon

 

[MaXJohnson]

The narrow spacing of your upper arms at the axle should almost eliminate the side-to-side torsional axle bind that is a problem with traditional 4-link designs. Yours should be almost as good as a three link in this respect. In any case, I would still use a joint with a little compliance at at least one end of the control arms. Heims at every joint forces what ever binding does exist to bend/deflect mounting brackets and arms.

To check for pinion gain, you could glue a chunk of PVC on your axle tube (black PVC) to simulate the pinion.

 

[Beezil]

I am terribly biased when it comes to xj front end link set-ups, but the bind issue is EASILY solved using a single center joint for the upper axle end, that can articulate in 2-axes....and even compliant in the 3rd.

 

[MaXJohnson]

I am terribly biased when it comes to xj front end link set-ups, but the bind issue is EASILY solved using a single center joint for the upper axle end, that can articulate in 2-axes....and even compliant in the 3rd.

Then...

hopefully, when you get the patent infringement suit with McDonald's settled, you can get that golden arch into production and out in the market place.

 

[Beezil]

I was given an "okay" since my name is McDonald

 

[Kaczman]

B- Your Golden Arches parabola wishbone is looking more and more appealing. But, right now I don't want to copy all the cool kids and their 3 links.

Did your mom ever tell you something wasn't possible, and you HAD to try everything imaginable to prove her wrong? Well, I'm gonna beat my head into the 4 link wall for a while longer. It has me in a figure four leg lock on the garage floor, but I'm not tapping out....yet.

I may not be very smart, but at least I'm stubborn.

-Jon

 

[Beezil]

hear me right!

I am not pushing the 3-link!

I'm your #1 fan right now, I think it would be cool if you can get a true 4-link to work.

It is a real challenge on all levels.

any comments I have are just attempts to illustrate what I founf when i was going through the design stages.....

the fact that I ended up with a 3-link was either me surrendering to the challenge, out of laziness and exhaustion, or it could be that the 3-link is actually the way to go. I have no idea which sitaution is more realistic

keep plugging away, but I think at this stage you need to "dry fit" your front axle under there....


do you have it? maybe I missed it.

 

[Kaczman]

Before I mocked up the PVC/plywood axle, I had the Waggy 44 underneath. Since it is low pinion, I don't see any link and driveshaft interferance. Pinion angle may be an issue.

On a side note---- will low caster affect full hydro steering if I don't get a balanced (double ended) ram. I'm planning on an orbital without return to center and a single ended ram. Less than 5 degrees of caster will make the pinion angle less of an issue for me.

I think the oil pan and exhaust clearance issues will be solved with the wide upper frame mounts and having the axle relocated so far forward. The chalenge is going to be in getting enough triangualtion to lacate the axle and not have any any binding issues.

I finished the last 10" of subframe today (where the stock LCA mounts were), and I'll see if I can get some frame mounts tacked in place in order to see what binding issues I may run into. I may use Max's advice and use JJ's at the frame mounts. I have 4 of them laying on the work bench from the old arms.

I "think" I can get it to work. It's a matter of getting the geometry laid out correctly.

-Jon

 

[BrettM]

On a side note---- will low caster affect full hydro steering if I don't get a balanced (double ended) ram. I'm planning on an orbital without return to center and a single ended ram. Less than 5 degrees of caster will make the pinion angle less of an issue for me.


-Jon

just cut and turn the knuckles! for the amount of work you're putting into a 4 link, I would think an hour with a grinder and 15 minutes with the MIG wouldn't be a big deal....

 

[Kaczman]

Yeah, turning the knuckles shouldn't be a problem, but if caster is not an issue with hydraulic steering, I don't want to do more cutting than necessary. Besides, if I'm already cutting on an axle, I may as well get a HP 44.

-Jon

 

[MaXJohnson]

I'm a big fan of > 5° castor, but assuming this is a trail-only Jeep, castor shouldn't be that big of an issue. Your larger tires will lower the DW window to the 30-40 MPH range, but with good steering joints, hydro steering and plenty of chrome stabilizers with bright red boots, you probably won't have to worry about it.