3 linking a 3rd gen

Theblackflag

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#1
So as many of you who follow me on Instagram know, I recently redid my rear suspension setup and converted it to a 3 link. So before I get into the tech portion here's a little background on the project, why I decided to go this route, and what my goals for it were. If you don't like reading then this thread won't be for you, there's a lot of info.

So I do not run sway bars on my truck, I snapped the rear one in half and the front originally had disconnects but they were a pain in the ass to hook up anytime it wasn't totally dry and when they were hooked up they always rattled and clunked. As a result of the no sway bars I had a ton of body roll, so much so that I was consistently putting a tire in the air when I was going around corners and driving mountain passes were downright scary. So there's issue number one, too much body roll

Issue number 2, terrible geometry and roll steer. I only have about 3 inches of lift on my truck in the rear but even with a relatively small amount of lift, it was enough to really screw with the geometry. With my 10 inch stroke shocks and roughly 17 inches of articulation in the rear when the axle fully flexes the axle would be pulled so far out of alignment by the giant amount of roll steer that my tire that was being stuffed would be jammed almost totally into the rear of the wheel well and the drooped tire would be pulled forward and basically under my slider. Sound familiar? I'm sure it does. This was also really present when I was driving especially on the highway and amplified by the excessive body roll, anytime I would go through a turn at speed I could feel the rear end shift and grab forcing me into the turn almost like rear steer. Doesn't sound that bad but sitting in the drivers seat was super sketchy.

So issue three, the rear links. Late last year I swapped out my lower control arm bushings in favor of SPC x axis flex joints. I did this because they were sealed and low maintenance. Well, this proved to be a mistake. By July of this year they were starting to wear out and on a big trip in Colorado about a mile into Engineer pass the races completely failed causing a significant amount of slop and a huge clunk anytime I hit a bump in the road.

So if you're following along Ive got 3 major issues with my rear suspension and it was only getting worse. Late July I was looking at getting it fixed and at the time Josh of 530 motorsports was running a special on his solid aluminum links that I decided to get in on. As luck would have it I ran chinamans gulch the day after ordering the links and did this.
IMAG0274
by Phoenix Black, on Flickr

So at this point replacing the rear mounts is a must since the mount had been so smashed and mangled over the years that I couldn't get the joints out. Well if I'm going to replace the mounts I might as well gain some clearance, but to do that I have to rework all the geometry. Enter the 3 link. I choose to go with a 3 link because I do not plan on running the f150 fuel tank for a few reasons but mostly due to the fact it is kind of a pain to make work with the stock fuel gauge and just adds a potential point of failure on the trail. I've learned to wheel with the stock tank and it has proven to actually be helpful when snow wheeling due to the floatation. After talking with @AssBurns and bouncing some ideas off him I started playing around with the 3 link calculator.

First was measuring the stock setup to get a baseline and here is where it measured out to be
Screenshot (5)
by Phoenix Black, on Flickr

As you can see the geometry is pretty shitty, the roll axis angle in particular, 10 degrees is incredibly high, and that's only with a 3 inch lift!

So after spending a lot of time under the truck measuring what was feasible to change and with an overall goal of decreasing roll steer and body roll I settled on this design that moves the lower frame mounts up and forward 1 inch, the lower axle mounts up and forward 1 inch. and the frame side upper down and forward 1.5 inches.
Screenshot (6)
by Phoenix Black, on Flickr

This provided much less roll steer, and also got the anti-squat back into a more desirable range.

So onto the fabrication side of things...

First up was correcting the panhard, as we all know the panhard geometry gets way out of wack even with a small lift. @eimkeith makes a great kit to fix this, but in my case, I didnt want to use a drop bracket as it lowers the roll center slightly which increases body roll. I also knew that with my extended @Plastics Guy bumps I had the room to correct the height by only lifting the axle side mount, by 2.5 inches to be exact.

By doing this I accomplished two things, first I moved the roll center up by roughly an inch which makes a huge difference in the amount of body roll the truck has because it shortens the distance between the roll center and the center of gravity which I have estimated to by roughly 36 inches on my truck. The second thing this accomplished was leveling the bar. This is super important because it puts the bar back at the longest point at ride height. This measurement of the peak arc width is the saggita. The sagitta is the vertical line from the midpoint of the chord to the arc itself. It is a measure of the 'height' of the arc. The length of the chord, sagittaand radius of the arc are inter-related, and if you know any two you can calculate the third. Thats the official definition for those who care. But its also what causes the "dog wag" many experience after a lift, since the bar isnt level the arc it travels in is larger causing the vehicle to shift or "wag" side to side

In addition to raising the bar mount I extended it by an inch to get the axle perfectly centered. This was more for

Here's a really good video that explains the panhard system really well and is what I used as a guid for setting mine up

Here's my raised bracket and extended bar

IMG_0163
by Phoenix Black, on Flickr
IMAG0284
by Phoenix Black, on Flickr
I later filled that gap in with weld and ground smooth. The solid bar inside also extends 6 inches in either way, rest assured it is plenty strong.
 
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Theblackflag

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#2
So with the panhard addressed it was onto the axle mounts. First up was the upper mount since I would be reusing the stock axle mount.

I didnt want my mount to look like @theesotericone so I spent some time reinforcing the sides and adding a gusset. I also added ruff stuff weld washers just like all the other mounts so the holes will never oval out.

@theesotericone's mount for reference
e5EOL49
by Phoenix Black, on Flickr

Beefed up stock mount
IMG_0159
by Phoenix Black, on Flickr
IMG_0161
by Phoenix Black, on Flickr
IMAG0566
by Phoenix Black, on Flickr

With things sorted on the axle side mount and all the stock brackets cut off from the frame, fyi an air chisel will be your best friend when removing the lower link rock catchers, I put the axle under the truck and started mocking up the rest of the 1/4 inch steel mounts. Now, here's where I don't have many pictures or much to say. A lot of it was just hours moving things around, cycling the suspension, and repeating until it all worked perfectly. So if you have questions ask away, I'll be more than happy to answer them

So here are some more pictures
Full bump
IMG_0170
by Phoenix Black, on Flickr

Under its own weight
IMG_0174
by Phoenix Black, on Flickr

Links mocked up
IMG_0168
by Phoenix Black, on Flickr

Old links next to the new ones. I used metal cloak bushings in the lowers and 2-inch ballistic joints in the uppers
IMG_20181006_183029_173
by Phoenix Black, on Flickr

Ride height. Notice how level the bar is
IMG_0179
by Phoenix Black, on Flickr

And lastly, after checking the measurements here is the final geometry. Slightly higher antisquat than I wanted but it drives well and everything else is pretty close to where I wanted it
Screenshot (7)
by Phoenix Black, on Flickr
Thats all the pictures I feel are relevent but the rest of the album can be found on my flicker page

So how does it drive? Its a totally different truck, my body roll has been at the least cut in half if not more, it drives better now than it did with the front bar on. I have also noticed I now have a bit of understeer, but I think this is because I have significantly less roll steer which is fantastic. Its an absolute dream on the highway, tracks straight and just feels super solid.

So as of now that's all I have, I haven't gotten to test much with the truck, just daily driving and some rough dirt roads, but in the next week or so Ill have some more feedback on how it turned out. I also am thinking of making a mount kit for this if there is enough interest. So Ill let you guys ask away with questions now.
 
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eimkeith

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#3
you know my PCK starts with a 2" raised axle-side bracket, right? the frame drop is for 3.5 to 4" lifts, as you can only go 2" without hitting the upper crossmember at full articulation Driver.. :)

I'll put up my 3 link measurements as well - they might be good data for you (and I'm into 3-Link, although I'm going 4)
 

Theblackflag

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#4
you know my PCK starts with a 2" raised axle-side bracket, right? the frame drop is for 3.5 to 4" lifts, as you can only go 2" without hitting the upper crossmember at full articulation Driver.. :)
Yes, I am aware of that, guess I should have phrased that better, with my given bump stops the 2.5 extension I have just barely clears but it worked out perfect for my case. Post up that data though, the more info we get here the better
 

eimkeith

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#5
ok, so here's my 3-link investigation file - it uses a much longer upper link to correct for roll steer, but compromises factory muffler use (it uses a frame mount for that link - exhaust has to be custom)

and next are my measurements for the factory suspension at 2" of suspension lift. things start to go funny at 2, can't imagine what happens at 3 :)
 

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eimkeith

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#6
also, how'd you post your screenshots? that's so much more user-friendly than my attachments... !

also - just checking your calcs - if you lengthened that upper and lowered the frame-end
mount a bit, I think you could get the AS and RA where you want them. (but I'm new to this stuff also, could be mistaken)
 

Theblackflag

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#7
windows key and the prt sc button takes the screenshot. I upload everything to flicker and then to here

I like what you did with the fix, the geometry looks really good as far as roll axis and anti squat go. my only concern is the upper link forward mount. What is, or was since your going 4 link, to get around that cross member that's there if you keep the stock tank?
 
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AssBurns

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#10
This is awesome! It turned out so well, especially with the badass aluminum links. I’m a little jealous of those.

I bet you still have oversteer, but having so much less of it is probably making it feel more like understeer compared to the crazy oversteer you had before. Just goes to show how bad the roll steer really is with stock geometry.

That upper link gusset and plating turned out well too! Maybe you can make a set for @theesotericone to fix his broken shit.
 

theesotericone

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#11
That upper link gusset and plating turned out well too! Maybe you can make a set for @theesotericone to fix his broken shit.
My broken shit will be fixed next week. It will also be re-enforced. As soon as @eimheith gets me the lower link mount re-enforcements those will get done. Then we'll see what else I can break. lol
 

AssBurns

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#12
My broken shit will be fixed next week. It will also be re-enforced. As soon as @eimheith gets me the lower link mount re-enforcements those will get done. Then we'll see what else I can break. lol
I’m sure having 35’s soon won’t help the breakage aspect of things.
 

theesotericone

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#13
I’m sure having 35’s soon won’t help the breakage aspect of things.
It might help. Bigger tires roll over shit easier. That's my theory and I'm sticking to it. I'll keep breaking this rig till I get sick of it then I'll build a real crawler. You know, one with a solid front axle. lol
 

eimkeith

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#14
My broken shit will be fixed next week. It will also be re-enforced. As soon as @eimheith gets me the lower link mount re-enforcements those will get done. Then we'll see what else I can break. lol
you still need that upper link mount? I'm cutting it off this weekend (already got measurements from it, now its in the way) :)
 

theesotericone

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#16
you still need that upper link mount? I'm cutting it off this weekend (already got measurements from it, now its in the way) :)
I don't think so. I'm pretty sure the current one can be bent back to shape. I'll no more next week. If you want to put it in a corner until then I'd appreciate it.
 
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#19
Curious why you didn't push the upper link mount way forward as well as extend the lowers more? I'm curious how much roll steer you get, correct me if I'm wrong but that's purely a function of link length since as the axle flexes the arc of the link pulls one side forward and pushes the other side back, and it seems you didn't significantly increase the length of the links? Likewise seems like a marginal increase of the upper link length, which the upper link in my experience is the direct limit to maximum droop since it goes vertical so far? It seems like you could of had a lot of room to move the upper link mount forward on the frame and get your roll axis angle down to 0 or even negative potentially? Curious how it does, and not bashing it, just wondering why you did certain design choices. Also, I fully admit my exceeding lack of knowledge of link setup and suspension design.
 
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AssBurns

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#20
Curious why you didn't push the upper link mount way forward as well as extend the lowers more? I'm curious how much roll steer you get, correct me if I'm wrong but that's purely a function of link length since as the axle flexes the arc of the link pulls one side forward and pushes the other side back, and it seems you didn't significantly increase the length of the links? Likewise seems like a marginal increase of the upper link length, which the upper link in my experience is the direct limit to maximum droop since it goes vertical so far? It seems like you could of had a lot of room to move the upper link mount forward on the frame and get your roll axis angle down to 0 or even negative potentially? Curious how it does, and not bashing it, just wondering why you did certain design choices.
Roll steer is effected by much more than link length. Having the lowers triangulated as it goes forward will reduce the roll steer, as it changes the axis and instant center of which it pivots around. Also the height of the links can change how the roll steer behaves at ride height. Long, Flat, Triangulated links will pretty much eliminate roll steer. He did all of those things to a small degree. He extended his lowers a hair, his lowers are parallel rather than reverse triangulation, and he made the links a little flatter at ride height.
The reason he went with the design he did was A) He bought the links from 530 Motorsports before he decided to take on this project. B) It was much easier to go this route than buy new links, buy and relocate the muffler, and easier to work around the stock crossmember.
You are correct that the upper links are the limiting factor on droop, but he did lower the upper frame side mount down and forward 1.5". So it's a hair longer and lower, giving him more room to droop. He isn't planning to achieve mega travel numbers, he is only trying the increase the performance of what he has to work with with the least amount of effort. I think he did a kickass job at that.

Correct me if I'm wrong on any of this @Theblackflag
 
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