Triangulated 4 link question

[mitch_04]

Hi everyone,
First off I'd like to thank everyone who posts on this site, I've learned a lot by browsing around. I'm about to build my first triangulated 4 link, although it isn't going to be on a pro-touring car. The suspension will be on an 85 C-10. My question is about the upper links. I have read that you do not what the axles upper links near the frame, you would want them near the differential. The reasoning for this is, I believe, that it would have an infinite instant center.



My question(s) is this: If I were to mount the axles upper links near the frame, what would the "seat of pants" difference be while driving? If I could go this route I would be able to mount longer links at a greater angle, helping me stay centered throughout the entire range of travel. The pickup will be bag on bar, and my main goal is to lay frame for shows with my secondary goal to be getting the best geometry available without hindering the main goal. If I have to go with the links near the differential, I would have to go much, much shorter since the frame is very narrow.

I do plan on building a pro-touring third gen Camaro, but until I find one in my price range I will learn on my pickup project.

Thanks for the help,
Mitch

[mitch_04]

50 views and no replies, it must be either a very dumb question or a decently tough one. I saw my terminology was incorrect, what I'm looking for is in instant center, but roll center. What would the infinite roll center feel like to the driver. If I'm missing something here, please correct me.

[exwestracer]

Mitch, the "infinite" roll center really isn't infinite. Sorry I didn't get back to you on this over on Lateral G. Wherever the upper links converge is the "fixed" point in the system. Everything revolves around that point. Let's say in your case the converge point is 48" ahead of the rear axle. If the rear really flexed out (like with a 4 channel air system), you would see some side motion of the axle. If the link angles get below 30 deg (60 deg total) you will be putting a lot of strain on the rod ends or bushings in hard cornering. In everyday driving, you probably wouldn't notice.

[Rod]

pick ups are HOT now keep building, having the upper links closer to the frame and further away from the pumpkin will create bind and that can be reduced with the use of hiem joints, but the centering advantage of having a triangulated 4 link is reduced now making the system closer to a parallel 4 link an will require a centering device such as a panhard, watts or mumford link

[mitch_04]

If I go with my upper axle links near the frame, and build a crossmember with a driveshaft loop, I will be able to have my front upper links, which would be triangulated, very close together. The links I'm using have a bushing on one end, and a "super pivot" on the other (think Johnny Joint). This should help my deflection, and I'll probably run the bushing on the frame side to help with transmitted vibrations. I should have no problem getting 60 degrees with my crossmember mounted front links. I don't plan on ever running air low on individual corners, and I doubt I'll every corner hard enough to get bind. This pickup will be mainly a fun project that hits the ground for shows, and looks good for cruising. I'm going to plug in the specs for the front end into the suspension analyser and see if there is anything I can tweak there as well.

Thanks for the help everyone, I'm diving in this weekend so it was great to get the info in time!

[mitch_04]

Well, I spent the better part of the day with graph paper and a ruler. The old leaf spring suspension is out, lower links are mounted on the new-old 12 bolt axle, and I just have the upper links and new crossmember left. I ended up with lower links parallel to the ground, 30", uppers are 70% of lowers from side view with 60 degrees between them, and angled down to give me a roughly 60% anti-squat. Lowest spot on the frame is about 7-8" off the ground at ride height. It's incredibly exciting finally seeing it at the height I've dreamt of since I began the project.

[exwestracer]

"like"

[MonzaRacer]

Im have Ridetechs parallel 4 link and I am looking into redoing it and using a Fays2 style Watts link later on and doing away with Panhard bar. But time and funds and how my knee and shoulder heal.

[mitch_04]

If I ever build another slammed pickup, I'm going to go crazy on the suspension. I don't know if you've seen a double Watts link, but they look pretty insane. I'd also have a cantilever setup and just generally have fun with it, care a little less about performance, more about style.

Anyways, I had to do a little modifying from my original plan as I built it. I haven't been able to do much measuring, but I think I'll still be OK. One big mistake I made was my rims and tires. I designed the suspension around the wheels and tires I will be buying, which will be an 1.5" inches taller. When I leveled my lower links, I didn't think of that, so I will have to adjust the mount down the road, raising it .75". My pinion angle may be off a little bit as well, but I left 3/8" threads showing on all my links so I can adjust that back into spec. Now everything is tacked in, I didn't have time to finish weld or mount my air springs, but that shouldn't take much time. Unfortunately, I have National Guard drills next weekend and the obvious, Super Bowl! I may sneak it in the shop during the week, we'll see. I might get some pictures on here, but I'm not very happy with how some of my welds turned out. It'll be strong enough, but they aren't pretty in any way.

[exwestracer]

If I ever build another slammed pickup, I'm going to go crazy on the suspension. I don't know if you've seen a double Watts link, but they look pretty insane. I'd also have a cantilever setup and just generally have fun with it, care a little less about performance, more about style.

Anyways, I had to do a little modifying from my original plan as I built it. I haven't been able to do much measuring, but I think I'll still be OK. One big mistake I made was my rims and tires. I designed the suspension around the wheels and tires I will be buying, which will be an 1.5" inches taller. When I leveled my lower links, I didn't think of that, so I will have to adjust the mount down the road, raising it .75". My pinion angle may be off a little bit as well, but I left 3/8" threads showing on all my links so I can adjust that back into spec. Now everything is tacked in, I didn't have time to finish weld or mount my air springs, but that shouldn't take much time. Unfortunately, I have National Guard drills next weekend and the obvious, Super Bowl! I may sneak it in the shop during the week, we'll see. I might get some pictures on here, but I'm not very happy with how some of my welds turned out. It'll be strong enough, but they aren't pretty in any way.

Mitch, please explain the "double Watts link" you are referring to. I designed one for a student to hold the airbag itself in place. I've never seen another one, so I'm curious. Got any photos?

[mitch_04]

I saw it in "How to make your Muscle Car Handle". I don't have any pictures, and maybe there is an actual name for it. It is like having 2 Watts links, one on each axle tube, and linked together in the middle. It is suppose to nearly erase the small bit of movement you get from a regular Watts link. I don't think it's complexity is worth it's benefits as far as manufacturing goes, but it definetly looks cool.

Unfortunetly, it looks like I will have to re-do my upper links. Somewhere between the graph paper and the welder my measurements changed and they need to go wider on the axle.

[exwestracer]

I saw it in "How to make your Muscle Car Handle". I don't have any pictures, and maybe there is an actual name for it. It is like having 2 Watts links, one on each axle tube, and linked together in the middle. It is suppose to nearly erase the small bit of movement you get from a regular Watts link. I don't think it's complexity is worth it's benefits as far as manufacturing goes, but it definetly looks cool.

This?

[mitch_04]

Just out of curiosity, or maybe future reference, how would you set up those? A regular watts link should have the bars parallel at ride height (I think), but those seem to be 45 degrees.

[mitch_04]

Y'up, looks a little different in the book but operates the same. I looked it up and it is called a Mumford link, was already posted earlier in this thread and I didn't even notice!

[Norm Peterson]

I believe you set the two long links to be at mirror-image slopes to each other (with the long links being of equal length). The same really applies to a Watts link, with "horizontal at static ride height" being the unique situation where the mirror image to exactly horizontal is . . . exactly horizontal.

Didn't see this until today.

Maybe I missed it, but is there any plan view skew to your lower arms? Whether there is, and if so which way they converge will make for changes in axle steer and some differences in feel. Something else to think about, beyond whether the axle will shift laterally by enough to notice (and FWIW I'd build a little extra margin into all of the brackets as the plan view angle between the uppers drops much below 90°).


Norm

[mitch_04]

I'm still trying to catch up on some of these terms. Plan view is overhead, and by skew are you asking if they are at an angle? My lower links are parallel, and the uppers are triangulated. I need to bring it back in the shop to remount something things. I raised my rear axle until it bottomed on the c-notch to make sure my brackets would clear the frame, but I had my pinion angle at 3 degrees when I tacked my upper brackets to the axle. Of course, when I lowered it to ride height, set my pinion angle back to 3 degrees (I didn't have my uppers installed yet, just mounted brackets) now my brackets were way off.

The next day I spend in the shop will consist of making small "jack stands" to hold the frame at ride height. I had been using our lift, but it apparently has air in it and likes to settle during alignment, which makes trying to figure out why your angles are off very tricky. Next I will put 3/4" wood under the tires to simulate the 1.5" taller tire that will be on it later and re-level my lower link frame bracket. It should just need to come up the same 3/4". Next I will raise the rear end to the highest it will go and re-mount my upper links so that they are wider on the axle end. I can't go any narrower on my crossmember, my driveshaft has to pass through and since the 12 bolt rear ends pinion is offset about an 1" of centerline, I have to go wide.

Just wanted to say it feels awesome to have some of the (in my opinion) experts of the forum answering my "beginner" questions. A lot of the time the experienced people don't want to spend time with simplier questions.

Also, I won't be running a Mumford on this, I was just curious in case I find someone who wants me to build a wild rear suspension. I'm thinking the Mumford and some cantilevering with horizontal coilovers would fit the bill.

[exwestracer]

Mitch,
On the Mumford setup, the link angle defines the roll center height (much like your triangulated links define the R/C location). Other than that, the links don't "have" to be at any particular angle. Check out the "Separating ride from roll" thread in the Advanced Performance forum.

[mitch_04]

Alright, back in the shop today and hitting a bit of a road block.

Question #1 - If I'm not able to get a full 60 degrees between links, what is the downside? Lateral axle movement, binding, or...?

Question #2 - I have my lower links mounted directly below the axles, center of joint being about 2" below bottom of axle. I may be able to get closer to 60 degrees if I take the upper link mounts, which are currently locating the upper joint directly above the axle, and move them closer to the front of the axle, rotating them forward from a side view. This will decrease my torque effect, but will it be a problem since the upper links are in tension during accel and only really hit hard during hard braking?

My C-notch is limiting my ability to go wider, but I have room ahead of the axle in the C-notch area. I could go wider if I go more towards the front of the axle with my upper mounts, vs being on top of the axle currently.

I checked on binding by setting my pickup at ride height and jacking up one side until the top of the axle hit the c-notch, no binding. This is through a 10" range of motion, something that it would probably never see unless I'm parking it crazy at a show. Gotta love them Johnny Joints!

[exwestracer]

1) More likely to have some lateral movement, but the upper johnny joints will help with that.
2) How close to 60deg are you? The amount you could gain by safely rotating the link mounts forward probably won't help all that much.

[mitch_04]

I wish I could draw on here, basically when my pickup is slammed for show I have about 2" ahead of the axle before I hit the c-notch. I either have the upper link mount directly above the axle and inside the frame, or rotate it slightly forward and it allows me to go about 1-2" wider. I was only at 42 degrees :( I have shortened a couple brackets that allows me to get a little closer on the front upper links, and also a little wider on the upper rear. I'm not going to change my link length, I'm at about 75% of the lower, so I'm trying to shoehorn the brackets as close as I can. Luckily, the pickup will never get driven at it's lowest setting, so if I do rub a bracket I'm ok. It will have about 8" of clearance at ride height. Hopefully I will have a pic by the end of the weekend of a finished rear suspension, even if it is just tacked in.