Simple DIY 3-Link Using Factory Mounts Build (1 Viewer)

[snivilous]

This seemed like something super cool I'm playing with that should maybe get more attention than my build. Backstory: I'm building a FZJ80 to race King of the Hammers and Ultra4, and as everyone knows the stock radius arms suck ass. I am allowed to run 14" travel shocks for my class, but the stock front setup seems to barely be able to use the travel of the ~10" OME shocks on it. I talked to 4WU because I like the looks of their kit, except I'm not allowed to run coilovers so would have to heavily modify their 3 link to use the stock spring perches and when I asked about just buying the dimensions so I could build my own 3-link with their specs, they said no way. I then talked to some guys who own big fab shops, and they said unless you're doing a full custom setup that it's not worth the time to try anything. Additionally, I researched a bit and found a few 3-link builds on mud but they were completely (or mostly) custom setups as well.

Well I didn't want a full custom 3-link, I wanted something reliable. I only have a few months until KOH, and having a reliable truck is the first priority. I have built my own long travel A-arms for my 4Runner before, and fell into the rabbit hole of realizing I didn't know what I thought I did (it eventually worked, but took a year of learning everything and tuning it through trial and error). I didn't want a repeat of that so more or less gave up the 3-link idea and figured I would do it next year. I already have 14" travel Kings on the way for the front and rear, so worst case I just didn't plan to use all the shock's potential in the front (the rear suspension is amazing stock so not worried about it).

THIS LEADS TO YESTERDAY! I was about to start putting my front axle back together that I had torn down since my last race a few weeks ago, and while I was cleaning up the axle to put the 3rd member back in I noticed how far back the radius arm axle mounts were. People had told me the stock radius arm mounts were too far under the axle to be usable for a 3-link... pretty sure that's totally wrong...

So here's the concept and why I started this thread: It is a common "hack" to undo one bolt of one radius arm on the axle side to flex more, well if you undo both front bolts on the radius arms and just add an upper link you now have a 3-link. I measured the radius arm dimensions from the stock frame mount to the rear axle mount and then measured where an upper link would theoretically sit on top of the pumpkin and where there would be room for a mount on the inside of the frame on the passenger side and this is what I got:

Now I am not a suspension expert by any stretch, but all the numbers seem to crunch VERY nicely. The anti-squat is right near 100%, I researched and wasn't sure of where the front anti-squat should be but with an adjustable mount that can go over or under 100% with minimal adjustment which is good. The roll center height seems to be low for my assumed CG, but the roll center seems to be a function of the panhard more than anything and I'm using the stock panhard so it should be fine I think. And everything fits BEAUTIFULLY when I was measuring. The upper link would clear the driveshaft, and the upper link mount would tuck in right under the motor mount. The last point is the tightest, but with the front bump stops about 1" lower than the stock cone ones it seems like it would be perfect.

The super exciting part of all of this is, to test it I just have to make one upper link and make two mounts (one frame side and one axle side on top of the pumpkin) and that's it! The stock radius arms with one bolt undone will work totally fine and act like normal links then! Obviously if this idea ends up working I would switch the radius arms to normal links, but the point is that this idea uses all factory mounting points and requires ZERO CUTTING. On a budget you could add the upper link and that's it and be totally fine theoretically. What is even cooler, is if for whatever reason this doesn't work, all I have to do is pop two bolts back into the radius arms and I'm back to the stock suspension! I wouldn't even have to cut out the brackets I welded on since they wouldn't interfere with anything!

Now the calcs from the 3-link spreadsheet only say so much, so I drew everything up in CAD to make sure it would flex and not bind up:

I am posting this for two reasons, if there are any suspension gurus in here I want to be critiqued on what I'm doing wrong. Surely someone has thought of this before and either I missed it or it's a bad idea right??? And two, if this ends up working I think a lot of people could benefit because this is a VERY simple, very budget friendly, very DIY friendly, and 100% able to convert back to stock without any trouble. It's literally a $150 3-link solution if you know someone who can weld (more if you decide to make new lower links).

I will be ordering heims, tube, and 1/4" plate in the next few days assuming I don't find a huge issue. I need to measure the stock radius arm mounts and bolts so when I (hopefully) swap the radius arms to normal links I can just use the same joints for everything.

If you have any comments or ideas please post! Please call me out if you see something stupid, but I have yet to find any blaring issues and I think this will be super cool and could help a lot of people get a sweet 3 link that's capable of handling massive shocks and only takes an hour or two to do! Stay tuned!

 

[JeepinPete]

A few things. Anti squat applies to a rear suspension. Using the calculator for a front suspension, you are calculating anti-dive.

Second, your roll angle axis is high. Oversteer is generally not desirable. As your steer into a turn, the suspension is going to effectively add more steering to your inputs. This results is squirrelly handling. Moving the frame lower mounts towards the center of the chassis, and flattening the lower links by moving the link mounts on the axle up will reduce the roll axis numbers.

Third, your rolling radius is not half you tire theoretical diameter.

As you said, it won't cost much to give it a try, but it has been done before here on Mud, and the results seemed to be so-so at best.

 

[SmokingRocks]

I think I spent a total of 600 on materials including hi-steer arms.

I still need to finish the panhard bar frame mount, But it works very well. My friend who is a master fabricator and has his own jeep product company did all of the work. He's done hundreds of three link conversions. I don't have his calc sheet but will see if I can get it. I liked that he moved the lower links frame mounts back, it helps it flex. He also ditched all of the factory mounts and made his own beefy mount brackets out of 3/8" plate.

Finally I was having a hell of a time finding a RHD steering arm for the double sheer setup, so Neil was able to successfully weld a lower bracket to the knuckle.

It's way dirty and some paint is peeling so don't judge me on that..

I bent the 1/4" DOM tie rod when I found a submerged rock in a river crossing

Hiem Joints are used for the steering.
Lower links uses: Hiems for the frame mounts and Jonny Joints for the axle mount
Upper link uses: Hiem on the axle mount and jonny joint for the frame side

The jonny joints were used to try and reduce the shock transfer from the axle to the frame.

Its been awesome off road

 

[snivilous]

Second, your roll angle axis is high. Oversteer is generally not desirable. As your steer into a turn, the suspension is going to effectively add more steering to your inputs. This results is squirrelly handling. Moving the frame lower mounts towards the center of the chassis, and flattening the lower links by moving the link mounts on the axle up will reduce the roll axis numbers.

Thank you for pointing those out, I looked into roll angle axis and concur with what you're saying. However, it appears that roll axis angle is purely a result of the lower link. Wouldn't my roll angle axis be the same as stock since I would be using the stock mounting points? As I view it the suspension is acting similar to stock with the exception that the axle can now rotate since it's not hard mounted to the lower links. I know that's over simplified, but since I wouldn't be changing the lower link geometry or the panhard geometry it seems like most variables would remain the same like the roll angle axis--is that not true?

 

[I Lean]

Your tie rod and radius arms (or lower links) might get friendly on droop? Something to keep in mind anyway.

 

[snivilous]

Your tie rod and radius arms (or lower links) might get friendly on droop? Something to keep in mind anyway.

Ooh good point, that might be the killer actually... hadn't even crossed my mind since the steering is laying off to the side right now.

 

[mudgudgeon]

I agree with @I Lean the tire rid might be a problem.
You can kludge together a fix using heim joints, spacers and bolt the tire rid to the to of the steering arm

I'm no suspension guru, but have a history of unusual, outside the square modifications to all sorts of things, but just cars.
The further you depart from the original design, the more work is needed.
There is no shortcuts without compromise. The bigger the shortcut, the greater the compromise.


In this image ^^^ your radius arms would be twisted out of parallel to the chassis, and out of parallel (front to back) in the diff mounting brackets.
Radius arms binding in the diff brackets is part of what limits their flex.
They bind due to twisting front to back, but also due to twisting top to bottom at the same time.
I think having the front bolt out, RAs will still twist, but the front is loose and may catch, or bind in the diff bracket.

I've seen modified front diff brackets that are spaced wider apart with washers between the bracket and the bush to allow the RA to twist more in the bracket.

The stock brackets are known to crack on the diff housin. Removing the front bolt will potentially increase (or change) the forces on the brackets.
You'd want to beef up the connection with some gussets, they are surprisingly thin.

I think you would probably be working with many compromises.
May be a good quick and dirty option to do some testing.
But I think a half assed solution that will probably not save you any work in the long run.

 

[BlueCruiser84]

Paging @nukegoat.

He said something to the effect of the factory RA setup with less than ideal geometry is much more forgiving than a 3-link with less than ideal geometry. I think the ideal budget setup would be to put the lower axle link brackets above the tierod like nukegoat did. This flattens your lower link and allows you to clear the tierod. The downside would be needing to run enough lift to make everything fit.

 

[BlueCruiser84]

I'm super excited to see where this leads. I've been kicking this exact idea around for about a year as I slowly put things back together.

 

[nukegoat]

BTDT - If you run less lift and smaller tires and just want more flex it would work. If you're running 37s and 5+ " of lift itll handle like garbage and feel sloppy and dangerous.

 

[snivilous]

Paging @nukegoat.

He said something to the effect of the factory RA setup with less than ideal geometry is much more forgiving than a 3-link with less than ideal geometry. I think the ideal budget setup would be to put the lower axle link brackets above the tierod like nukegoat did. This flattens your lower link and allows you to clear the tierod. The downside would be needing to run enough lift to make everything fit.

BTDT - If you run less lift and smaller tires and just want more flex it would work. If you're running 37s and 5+ " of lift itll handle like garbage and feel sloppy and dangerous.

It looks like if I raise the lower links 5" (which was just a number I guessed at sitting at home) then the roll axis angle drops to 0.99 at ride height and then I can drop the anti-dive down to 30% range which I've read is reasonable (and without much adjustment can vastly change that. If all I have to do is make new mounts for the 3 main links on the axle side, and one frame side mount that isn't that bad still.

Good handling at 60mph offroad is a lot more important than having a ton of flex for me. I plan to lift the front a few inches to make the truck level so I took that into account with my new numbers as well.

 

[richardlillard1]

I think I spent a total of 600 on materials including hi-steer arms.

I still need to finish the panhard bar frame mount, But it works very well. My friend who is a master fabricator and has his own jeep product company did all of the work. He's done hundreds of three link conversions. I don't have his calc sheet but will see if I can get it. I liked that he moved the lower links frame mounts back, it helps it flex. He also ditched all of the factory mounts and made his own beefy mount brackets out of 3/8" plate.

Finally I was having a hell of a time finding a RHD steering arm for the double sheer setup, so Neil was able to successfully weld a lower bracket to the knuckle.

It's way dirty and some paint is peeling so don't judge me on that..

I bent the 1/4" DOM tie rod when I found a submerged rock in a river crossing

Hiem Joints are used for the steering.
Lower links uses: Hiems for the frame mounts and Jonny Joints for the axle mount
Upper link uses: Hiem on the axle mount and jonny joint for the frame side

The jonny joints were used to try and reduce the shock transfer from the axle to the frame.

Its been awesome off road

Were you at Cruise Moab this year?

 

[SmokingRocks]

yup!

 

[JeepinPete]

The thing that jumps out at me with the revised numbers is the separation between the upper and lower links at the axle. It isn't very much. That is going to greatly increase the stress on the axle mounts. I seem to recall the general rule of thumb was 7" separation minimum. Obviously one can push that, but 4.5" is probably pushing it too much.

 

[nukegoat]

The thing that jumps out at me with the revised numbers is the separation between the upper and lower links at the axle. It isn't very much. That is going to greatly increase the stress on the axle mounts. I seem to recall the general rule of thumb was 7" separation minimum. Obviously one can push that, but 4.5" is probably pushing it too much.

7" is a stretch IMO. 4.5 is a disaster

 

[nukegoat]

It looks like if I raise the lower links 5" (which was just a number I guessed at sitting at home) then the roll axis angle drops to 0.99 at ride height and then I can drop the anti-dive down to 30% range which I've read is reasonable (and without much adjustment can vastly change that. If all I have to do is make new mounts for the 3 main links on the axle side, and one frame side mount that isn't that bad still.

Good handling at 60mph offroad is a lot more important than having a ton of flex for me. I plan to lift the front a few inches to make the truck level so I took that into account with my new numbers as well.

Yeah this works but you have no link separation as @JeepinPete said. And all mounts above centerline is hard on everything so its even trickier.