i've got a question for the suspension gurus and i hope that i've done enough homework to not have missed anything to major. i've done plenty-o-searches on the subject, even reading a little of the suspension god thread. i've also looked through an old SAE book on suspension and vehicle dynamics to try and verify my ideas. i think i've got a setup for a 4-link rear, and i want to make sure that i understood what i read and that this will not be a big piece of dog crap.

the 4-link is for my friend's cj-8 that is currently sitting on 4" springs soa'd front and rear. he wants to do coils or 1/4 elliptical on the rear, but wanted some help setting up the links to minimize rear steer and wheel hop. he has a model 18 t-case with offset d44/d60 from a '70s j20, and has a standard driveshaft.

to make it all work, i have suggested that he run equal length arms that are parallel from the side view. the arms will be at about a 19 degree angle from the ground at rest to follow his driveshaft angle. the lowers will be connected from a cross-member at the rear of the t-case to the horizontal centerline of the rear axle to prevent the arms from dragging too far below the axle. uppers will be mounted from a cross member on the top of the axle to the frame.

from the top view, the uppers will be in a V shape from the outside of the frame to the near center of the axle, and the lowers doing the opposite V from the t-case crossmember to the outside of the axle. to make things symmetrical, i suggested that the inner points on the upper and lower arms should be spaced in equally, and the same for the outers. this makes two Xs when looking from the top view.

with this setup i believe that the rear steer should be minimal due to the inverted-V pattern of the uppers and lowers. wheel hop should be minimized due to the parallel links on the side view, as this should minimize anti-squat. however, having the arms at 19 degrees will work against the parallel arms it will have some anti-squat, but this should beok as it seems that a little anti-squat can help the tires bite, but i don't want so much that the axle tries to go under the vehicle.

looking from the side view, the roll center should be just below the connection point of the uppers on the axle and the suspension roll axis should almost follow the driveshaft.

have i missed anything? we plan to use some dowel rod to mock up the arms and maybe a board in place of the axle to verify that it won't bind before cutting and welding on the real stuff.

Sounds like you did your homework. I totally agree with your anti-squat statemet. Also, one thing to keep in mind. The weight of gear in the back. When the vechicle becomes loaded with a bunch of wieght the ride height in the rear can change alot. This will, in-turn, change the anti-squat values. It sounds like you know, for the most part, whats going on. The GOD OF SUSPENSION thread is awesome! Post some pics when you get'em.

the nice part is that we can build it with it loaded for the trail since we are essentially swapping the soa springs for the 4-link and either coils or 1/4 elip. when we were taking measurements we threw the toolbox in the back, and the spare is always in the bed so we had a reasonable idea of what it would be like.

Originally posted by JohnnyJ
the nice part is that we can build it with it loaded for the trail since we are essentially swapping the soa springs for the 4-link and either coils or 1/4 elip. when we were taking measurements we threw the toolbox in the back, and the spare is always in the bed so we had a reasonable idea of what it would be like.

I don't know about you, but when ever I go wheelin I bring a lot more gear then a tool box and a spare tire. If this is the case with you, i'd throw some more weight back there for the mock up.

Sounds like a good plan so far. That's almost exactly how my rear suspension is set up. Equal length, parallel arms, the lowers are triangulated from the center of the vehicle (under the output shaft of the t-case) to the ends of the axle. The uppers are triangulated from near the center of the axle (I put mine just on either side of the pumpkin so I didn't have to deal with welding them onto a cast surface) to the inside of the frame rails. How are you building the control arms? I made my lowers from 1.25x.280 DOM sleeved with 1.5x.120 DOM, sleeved with 1.75x.120 DOM. I have been able to put a slight bend in one (to my amazment), so build em sturdy, and build a spare or two while you're at it.

Where can I find this GOD OF SUSPENSION thread to read?

Originally posted by 2manyJPs
Where can I find this GOD OF SUSPENSION thread to read?

THE GOD OF SUSPENSION THREAD (http://www.pirate4x4.com/forum/showthread.php?s=&threadid=7503)

That sounds a lot like the way my rear suspension is built, almost exactly in fact. One thing to consider is the lowers might be weaker that way, since the uppers pull and the lowers push on the gas. You're getting a weird angle on the lower triangles that isn't there with straight lower arms. Rear steer is almost non-existent. I got my basic setup done and haven't gotten around to adding in the gussets and boxing on the upper rear link tabs, and one of them bent a little bit on the first off-road excursion. So gusset that shit up!

thanks for the tips slagburn. i can't wait to get started on this project.

-snip-he has a model 18 t-case with offset d44/d60 from a '70s j20, and has a standard driveshaft.-snip-

Would'nt the driveshaft will be between the upper and lower links on the right passenger side?

Yeah, it will be between. We have to make sure that the upper does not interfere with the driveshaft, but I think the lower should not be a problem.

Tomorrow morning we are mocking it up in place using dowel rods and other high tech tools to make sure there are no clearance issues.

it is very likely that the lowers will interfere if the crossmember is close to the heigth of the t-case out put, but inboard of it. I have problems with my lower passenger side link when i was running it from the outside to the center of the crossmember, so what I did was move the lower links frame attachment points out until the passenger one is directly under the t-case rear output. This should be very similar to the double v link set-up to combat rear steer, let me know if you have a different outcome with yours

fcfred: when we were trying to mock it up over the weekend we saw what you were talking about. it looks like the only place to put the lower arm with this setup is right under the t-case yoke, but in order to make sure the control arm doesn't interfere with the driveshaft it may have to be dropped down considerably, causing a low point to drag on.

right now the owner has put the project on hold until at least after we get back from tellico (just b4 the july 4th). it works good enough for now, he just wants more flex.

it seems that it would be much easier of a project with a centered t-case output/driveshaft/rear axle...

edit:

duh, i forgot to mention that when we played with where to put the links, it looks like if the lowers were closer to the center of the vehicle it would interfere with the driveshaft while the pass side was compressed, and if we moved the control arm to the outside of the t-case yoke, then there could be issues with the 1/4 elliptical spring pack and maybe even the frame..

Well, it didn't take long for my friend to crack and for us to try again. He got done building the cross member and realized that it wouldn't be as bad as he thought, so last night he called and we started to set it up.

We've got the lower mounts on the crossmember welded on, and it looks to be about 25degrees side angle from the point directly under the yoke to where the springs currently are. we plan on making a combo lower control arm mount and shackle mount that will sit where the springs currently mount. the bracket will have a mount for the control arm on the forward face and the 1/4elip shackle on the rear, both will be at the height of the centerline of the axle tube.

for the uppers we plan on building a tower on the drivers side of the axle, and then using 1/4 plate to run from the tower, across the top of the diff, and then bend it to meet up with the passenger side control arm mount bracket. this should hopefully keep the upper mounts as low as possible, and that will determine how far up the frame the upper control arm mounts will be.

all arms will be the same length, and it looks like there will be about 10 degrees of rise on the arms, making them as flat as we can while not having them hang lower than needed.

anybody see any issues?

Weekend progress update. We hooked up the lowers and all four arms are built. We hope to have it done by next weekend or so.

http://www.msg4x4club.com/members/member_pics/indy/lowers_mounted.jpg

Here's a couple of more links if you want to follow them.

http://www.msg4x4club.com/members/member_pics/indy/axle_mount.jpg
http://www.msg4x4club.com/members/member_pics/indy/tcase_xmember.jpg

Everything looks to be fitting in. So far we haven't found any problems that couldn't be solved. The lowers are connected similarly to what fcfred said; it is directly below the t-case output and connects where the spring pads used to be.

We built a bridge that goes over the pig that the uppers will be mounted on. The uppers will be about 3" apart on the axle side and mounted about 1/2 off the frame.

Here is my redone RE long arm.

http://www.beast40.com/JeepPictures/j323.jpg

http://www.beast40.com/JeepPictures/j324.jpg

johnny j
looks great
I haven't gotten anything done on mine in a while
keep us posted on your upper axle mounts

I'll try and remember to drag the digi cam over there again tomorrow night. the axle brackets are all welded on and we are going to set up the frame mounts for the uppers and then maybe mount the coils if we have time.

hey beast, I just noticed you are from g-boro. I spent about 6 years there. went to guilford college and then lived on Guilford ave down by uncg, boy I miss the south. Is PO-folks still open over by the collesium? Mmmm good eatin down there
hows the weather?

Another night of awesome progress. When I left we had it sitting on the coils, but the upper bucket isn't done yet. He also needs to figure out where the fuel pump and filter and muffler will run, they were both in the way of the upper arms.

Here's a pic of us testing the movement of the arms with no springs or shocks to interfere. the driveshaft is just placed in there to see the angles. At this point we had a hi-lift on the ass end with it lifted until the roll cage was almost touching the ceiling and then we used a floor jack to lift the axle. No binding and the axle moves almost perfectly straight up and down!!

http://www.msg4x4club.com/members/member_pics/indy/flex_2.jpg

Here's some more pics if you want to view them. The lowrider pic was to see how it would look if we slammed it.

http://www.msg4x4club.com/members/member_pics/indy/lowrider.jpg
http://www.msg4x4club.com/members/member_pics/indy/rear.jpg
http://www.msg4x4club.com/members/member_pics/indy/droop_1.jpg
http://www.msg4x4club.com/members/member_pics/indy/droop_2.jpg
http://www.msg4x4club.com/members/member_pics/indy/flex_1.jpg
http://www.msg4x4club.com/members/member_pics/indy/coils.jpg

ok, I gotta few questions for you
how long are your arms?
are they all the same length?
how long is your driveline and what is the angle?
is your t-case pointed down?
is the pinion pointed up?
does the angle of the pinion change as it moves through the motion?
does the driveline slip much?
thanks

well, its not my jeep, it's a buddy's but here's the details:

>> how long are your arms?
about 40"

>> are they all the same length?
yes

>> how long is your driveline and what is the angle?
driveline is a 4.2 / t-18 / d18, never measured the length. it's tipped slightly down towards the rear of the vehicle.

driveshaft is at about 15 degrees on level ground, arms are at about 10 degrees.

>> is your t-case pointed down?
yes, a little

>> is the pinion pointed up?
yes, hopefully not too much. it is at the same angles as before we did the conversion. he was running a spring over and claims he had no vibes so we left it alone

>> does the angle of the pinion change as it moves through the motion?
not much

>> does the driveline slip much?
huh? slip in which way?

sweet thanks
what I meant was does the driveshaft get longer or shorter as the axle moves up and down?

i forgot to look, and i'm too tired to try and figger it out in my head.

here's it ramping while we were trying to figure out shock placement and length. we had to limit strip the rear because the front hasn't been touched yet (other than soa) and it didn't want to flex. we've been talking about doing the front end this fall/winter, but this setup lifts the tire 8" higher than when it was soa front and rear and feels really stable even after picking up a tire

http://www.msg4x4club.com/members/member_pics/indy/rti_1.jpg

Here's a couple pics of the arms when flexing..
http://www.msg4x4club.com/members/member_pics/indy/rti_2.jpg
http://www.msg4x4club.com/members/member_pics/indy/rti_3.jpg

We're taking it down to Tellico on Saturday to test it out, so this should be the last of the driveway shots until we rip apart the front end.

Thanks to all the pirates that know their shiznit about suspension and wrote detailed posts about it; without it this would not have been a 3 week buildup and probably would have sucked.

edit - oh yeah.. we still have to gusset the hell out of the brackets. and that tire is lifted about 40" off the ground, good for about 770 on the 30 degree ramp. and i need about 4 more hours of sleep..

Hey JohnnyJ, looks good.:cool: What coils did you use? Estimated, how much weght do you have in the rear? Looking at doing the same but with it pushed back 8 - 10 inches. That's after I raise the gas tank.

they are stock front tj coils flipped upside down.


i'm not sure how much weight in back, but it sits pretty level with the fuel cell, 38" spare, toolbox, cooler and a few spare parts thrown in back. i'm guessing a good 400-500 lbs of extras? maybe more?

Originally posted by JohnnyJ
they are stock front tj coils flipped upside down.


Are they long enough to provide the travel that you wanted? Where did you get the buckets for the coils? Have you wheeled them yet? If so, how do you like them? Thanks for the help. Trying to decide on what I want to do with my rear end.
Stemp

:flipoff2:

Uhh WTF?

Why bring up an old ass topic like this, and not add ANYTHING TO IT?!

Get out of her newbie, stop padding...

Actually I found this one by flipping through old pages. I ran a search and couldn't find it again. I tried the "subscribe" button but it didn't seem to work, so I gave it a :flipoff2: and got subscribbed. I am about to start my own suspension upgrade and need refferance material. So BACK OFF JACKASS!!!:flipoff2:

SAE book on suspension and vehicle dynamics

Where can I find this book? You have any info on this?

Thanks.

And look it going through the cycle might have taught someone something. :flipoff2:

Originally posted by bad booger
...so I gave it a :flipoff2: and got subscribbed. I am about to start my own suspension upgrade and need refferance material. So BACK OFF JACKASS!!!:flipoff2: Uh... why not just do this instead of reviving a dead thread? :shaking:

Originally posted by Jeepin_NC


Where can I find this book? You have any info on this?

Thanks.

Try www.sae.org, I got the book when I took a class through work. It was written by Gillespie if that helps for searching.

Originally posted by bad booger

:flipoff2:


Thanks for adding such a useful comment. Can this thread die again?

My favorites list is a mile long. Who says its dead