Front 4 Link Modeling

Kaczman

Lurker
NAXJA Member
I'm still trying to squeeze a true four link in the front, and have finally gotten around to setting up a scale model. In the current model, the lower arms are 32" and the uppers are 26". My biggest concern is how much lateral movement the axle will exhibit while flexed. It appears there is 2.5" of clearance between the oil pan and pass. upper arm. If the axle moves vertically with MINIMAL lateral movement, I think it will work. The roll center is 5.5" in front of axle centerline.

Who knows which keeps the axle more centered when flexed; a high or low roll axis?








-Jon
 

Beezil

Member #Nay
NAXJA Member
no way in hell you'll squeeze a true 4-link under an xj with a 4.0 and adequate triangulation!!!!

prove me wrong!!!!

please!

best of luck to you, that is a real challenge.

try to figure out your pics, if you someone to post them, go ahead and e-mail me, and I'll help you out.

:D
 

JnJ

New member
I predict upper driver's side arm contacting the oilpan and exhaust. but then I really don't know much, so go for it and keep us posted on how it works.
 

Beezil

Member #Nay
NAXJA Member
I'll do what I can to help kacz make this a reality, but I just can't see it now....

this will be a good thread anyway....

lets continue.

can you measure the included angles of your upper links?

it appears as though the triangulation is not enough.

it does not look like you'll end up with a link system that will resist side load adequately.

also, have you tried to figure out roll axis?

lemme try to dig for my picture that shows the flat-pattern drawing of the "working area"

the xj is a real bitch.

I am rooting for you though.
 

Beezil

Member #Nay
NAXJA Member




the white chalk shows the "playing field" which I know you are quite aware of....

sucks doesn't it?
 

Beezil

Member #Nay
NAXJA Member
bumping the axle forward is good, you can gain an inch or so, but it doesn't mean "you're all set".....(i know yer were kidding)

there's wheelbase to think about.

I bumped my axle forward about two inches, bu then I wish I had two inches more to move my rear axle back, and at tat rate I'd have a wheelbase or what? 105-106?

no thanks.
 

MrShoeBoy

New member
Whats keeping you from moving the UCA frame mounts to the outside of the "frame rails"? That would give some more trianglation would it not?

If you really wanted to go nuts, you could design a new custom oil pan and exhaust to get the correct geometry for the arms.

AARON
 

zjmike

New member
Uh, why hasnt anyone done a reverse setup yet???



triangulate the lowers and have straight uppers??


with a High Pinion front axle, that would work fine..

OR you could do a triangle wishbone at the bottom..


come one , think out of the box a bit..
 

Kaczman

Lurker
NAXJA Member
I moved the axle forward 4"-- the current wheelbase is 108":eek:
Supprisingly, the passenger side arm is closer to the oil pan, the driver's is close to the exhaust.

The UCAs form a 48 degree angle ~5.5" in front of the axle (roll center) The arms are 26" long with 5 in. horizontal seperation at the axle and 27 in. at the frame. As you know there is NO room to run a long straight arm.

The roll axis is a bit concerning... 8 degrees up toward the rear. I'm worried with a somewhat low and steep roll axis the axle will shift on articulation. As it is now, the axle can move up 6.5" before oil pan contact. But, it CANNOT move laterally more than 2".

The lower arms are mounted just below axle centerline 38" apart, and inboard of the frame 26" apart. I hope the added triangulation of the lowers will help locate the axle.

Are any of the pics showing? I'll see if I can get em to work.


-Jon
 

MaXJohnson

New member
A little bit of movement at each joint will make a considerable difference overall.

You can move the lower arms up at the axle to about 1" above the axle centerline. Move the lower arms closer together at the chassis mounting point. More triangulation here will help flatten your roll axis.

Shorten the upper arms an inch or two to get them in front of the frame rail rather than inside the rail. This will allow you to move the mounting point at the chassis further outboard for added triangulation and a slight improvement in front IC. The wider base should also give a marginal increase to pan clearance. As mentioned above, modifying the down tube (exhaust) might help a little as well if there's room. I doubt you can do much with the pan short of going to a dry sump.

The suggestion of full triangulation of the lower arms with straight uppers would result in a very low roll center. This would increase the moment arm by about 8" - 10" and result in more body roll. You want less body roll, not more.
 

Beezil

Member #Nay
NAXJA Member
Uh, why hasnt anyone done a reverse setup yet???
what max said, and there some stiff penalties for articulation clearnace.....

i tired everything, and I'm not the first.

everyone told me it was a moot point, but I'm glad someone is giving it another go.

the responces are good, and smart, but you guys out there willing to help, cralw under your own rigs with some kite string, and snap some lines and you'll see what a bitch it is.

kacs, I'm still doing some varsity cheerleading for you......I'm trying to keep my mind open.

show me the way.
 

vintagespeed

New member
My original plan was to do the upside down 3 link with a triangulated lower. It'll work fine, LOTS of competition rigs that way. You'll have to get creative with the 'frame' end of the lower link though. My 3 link has a TB & 3 straight mid arms (like Goat's) but my upper is on the opposite side. I had some DW problems & thought I'd have to scrap it & do the inverted 3 link as originally planned (the DW was toe). I got under there & re-measured everything & you can fit a 3rd link under the driveshaft, with 1.5" dia tube it would cross 1/2 way down the shaft with about 3.5 - 4" clearance on my F250 HP D44 at ride height. That would be plenty to account for articulation (at least with my 38s).
 

Kaczman

Lurker
NAXJA Member
So, is there a good "rule of thumb" for minimum triangulation? I've searched around on POR, but due to the nature of POR, I haven't found a consistant opinion. Is the 48 deg. UCA angle, and the 25 deg. LCA angle enough to locate the axle laterally?

Shortening and lowering the UCAs would help, but with the short arms, the pinion starts to dive (esp. with driver's side drop). I have a LP Waggy 44, so pinion angle is a definate concern for me.

I'm trying to keep my mind open as well, but every time I crawl under the Heep, I hit my head on another obstacle.

I added a line drawing to the Yahoo site (if anyone can access it) to show what I have laid out currently.

Check out the following pics. I need to determine the best roll axis in order to prevent the axle shift in pic#1.





Keep the options comming.
-Jon
 

Beezil

Member #Nay
NAXJA Member
K-man.....

if there is one thing I have to say....

its go into it slow......

I know what its like to be baffled by link geometry....

shit i'm sill learning!

as you are designing, just make sure you build in some adjustments so you can have abll dialing it in.
 

Willis

New member
I'm still waiting for someone to go dry sump for arm clearance. Would solve the oil starvation at severe angles too.

I've been keeping an eye on these suspension threads. I am not quiet sure what I want to do with mine yet, but I hope you suceed and tell us all about it.

Good luck!
Steve
 
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