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Drive It Like Ya Stole It
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Discussion Starter #1
You know me, always up to something. Now that a majority of the SFA swap on my truck is done Ive all of a sudden found tons of free time. I know I have details to work out still but I cant help but look farther down the line.

What I mean by this is looking at 4 link design for the back. I have some knowledge of how a 4 link works but im not sure what will be best for my aplpication. Heres where I am now:

-It needs to be streetable - no questions asked.
-I would like to run equal length links if possible, so I can carry a single spare.
-I would like to have adjustable brackets so I can fine tune the links

Now here are the questions:
-what is acceptable antisquat, Ive read anywere from 60%-110%, 80% being about the average
-where do I want my roll center exactly, more exactly how high do I want it
-should I run triangulated uppers and lowers?
-Is the equal length link a good idea, alot of people say to run the top links 75% of the length of the lowers, this way your antisquat doesnt increase when your suspension drops out and in real world situations push your ass end up when in a climb or something.
-Whats your take on springs - coilovers, air shocks, half leafs... whats a good way to go.
-What size tube/ends. I want the lowers to be able to take a beating for sure, maybe as much as .5" wall tube.

Now some things to consider:
-I will be running a fuel cell so there will be no tank in the way.
-I will be hacking my bed and turn it into a removable skin with a flatbed so dont worry about room, ill make room.


Now I have alot more questions but lets start here. Also ANY input is welcome. Im in teh very very very begining of the design phase so ALL options are wide open.
 

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Drive It Like Ya Stole It
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Discussion Starter #3
well here is the plan. Im going to take the bed off and cut the sides off. Then I will build the links and coilover towers if I go that direction and a rear part of a eventual total exo cage. It will be designed so the bed sides will bolt right back onto the tube frame, and the trailgate will go on and function as a tailgate even. It will look almost normal except for the coilover towers and tube stickout out the top. When I go offroad, I will be able to pull the sides off so I dont rip them to shreds with the tires, bash them on a tree or kill them in a rollover or flop.
 

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Here we go.

Antisquat really depends on the vehicle length and weight. A buggy that weighs 3500 pounds and has a 110" WB would want low antisquat, around 50%. Whereas my truck which has 172" WB and weighs 8500 pounds likes around 95% AS. Mine is adjustable from about 70-130% through my brackets and I am happiest with the 95% area, I started around 80%. It stays almost perfectly level under any acceleration amount.

You want your roll center to slope downward very slightly torward the front and you want it as high as possible. The higher it is the less body roll you will have. One thing about roll center is that you can design your suspension to take care of tire clearances. If your roll center is really low, say around the centerline of your axle, the axle will roll on that centerline which can cause the tires to hit the bed/frame/shocks/whatever when articulated. Now if you move your roll center up, the axle will swing out as well as up which creates more clearance. I designed mine for the roll center that would allow the most tire clearance.

You should run as much triangulation as possible. If you run both triangulated you will eliminate most of the axle steer which is good. Axlesteer is something you see on every poorly designed 4 link, you can always tell guys that did their homework and guys that did not. Mine has no noticeable axle steer at all which I am quite proud of. Also the more triangulation you have the stronger forces you have holding the axle centered.

Equal length works great, your horizontal seperation can control your your mounting locations to control antisquat, look at my plans of mine to see this, mine are equal length.

Coilovers all the way. Airshocks are too weak for a fullsize, even Bill on pbb took them off of his buggy. They are not designed to take more than about 1500 pounds per corner at most. Half springs, known as 1/4 elliptical, work well but again, not great for a full size and they also promote alot of axle steer. Coilovers are the best way to go and you can run a tripple rate coil setup like I have to make your springs progressive, you can't do this in a 1/4 elliptical.

You will want a 1-1/4" heim on your links for strength under a fullsize. Problem is they will wear very quickly on the street but the 1-1/4's last pretty well as long as you keep them very well lubricated and clean. Putting baloons around them help out greatly. Problem with having a DD/trail rig with a 4 link is that with heims you will get all the shock loads the axle see's straight to the frame. It's pretty bone jarring. This also kills heims. Your best setup for a street rig is to use a heim at one end and a bushing or johnny joint style end at the other. I run large RE joints at the frame end and 1-1/4 heims at the axle end. This setup seems to be working well but I need new bushings in the RE joints already. Street driving killed them with all the shock loads from pot holes and such.

On your fuel cell, how do you plan on running a sender that interfaces with the ecm? Also what are your plans on the return lines, feed lines, intank pump, vapor recovery system, etc? After looking at all this I decided to go with a 42 gallon suburban tank, my sending unit/pump dropped right in and it fit perfect between frame rails.

Some good reading:

My 4 Link Build

My Bed Build - Includes Fuel Tank

My Thread on PBB About my System

In that last link there is a link in my first post that is good reading as well.

I definately suggest drawing out your design first and hand calculating everything through the formulas you can find on PBB or in any good suspension books, this way you only build it once and you don't look like a retard on the street when the back of the truck lifts up 2 feet when you take off from a red light and your rear axle doesn't try to walk under you truck sidways on the trail.

Good Books:

Chassis Engineering by Herb Adams
Race Car Vehicle Dynamics by Milliken and Milliken
 

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Dark Eternal said:
well here is the plan. Im going to take the bed off and cut the sides off. Then I will build the links and coilover towers if I go that direction and a rear part of a eventual total exo cage. It will be designed so the bed sides will bolt right back onto the tube frame, and the trailgate will go on and function as a tailgate even. It will look almost normal except for the coilover towers and tube stickout out the top. When I go offroad, I will be able to pull the sides off so I dont rip them to shreds with the tires, bash them on a tree or kill them in a rollover or flop.
That is the exact same thing I used to tell everyone. Then when it got to that point I said screw the bed sides, there heavy :D
 

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FEARS NO POTHOLE
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there is a guy linking his truck on desertrides.com an i like the looks of his cage.... he chopped off the rear part of the frame and is tubing the rest (common on desert trucks) for rock crawling i don't really now what is the best thing to do. i would defintly go with coilovers for the rear and build a swaybar to keep it streetable. ne ways here's the pic of the cage, with the straight tubing on the top i would imagine it would be pretty easy to make your bedsides work and it looks liek a pretty good setup minus the dual upright spares in the rear.
 

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FEARS NO POTHOLE
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willyswanter said:
That is the exact same thing I used to tell everyone. Then when it got to that point I said screw the bed sides, there heavy :D
just out of curiousity why didn't you ever go with fiberglass fenders, they are way lighter then the stock steel ones, plus if you use dzues fasteners they are pretty easy to put on and take off.
 

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Drive It Like Ya Stole It
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Discussion Starter #8
Ya know the one thing I havn't looked into at all is the fuel cell. Ill research it and see what I can find out. If not I can run some other tank. I dont need or want something as big as a 40 gallon. I was hoping to use a fuel cell because I wanted a long, narrow design. Like 54"x12"x12" - that would come out to just about 27-28 gallons, the same size tank I have now. That way I could place it right up against the cab like you would a tool box, and loose very little bed space.
 

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SkyRider469 said:
just out of curiousity why didn't you ever go with fiberglass fenders, they are way lighter then the stock steel ones, plus if you use dzues fasteners they are pretty easy to put on and take off.
Because I don't need them. There is no NEED for bedsides on my truck, even when I drove it on the street I wasn't hassled at all by cops because I ran mud flaps, they could care less if I had fenders or not. When I origionally built I put the bed sides on full length and it looked just like it used to before all the mods, but I wasn't into it. I have plenty of bed space in the "new" bed and I like the way it looks better without the bed sides.

About the fuel cell, why wouldn't you want 40 gallons? If you ever do end up getting into rocks/trails, you may be on a trail for 5 days... I'm running the Rubicon in a couple weeks and we will be on the trail, 40 miles from anywhere, for 5-6 days. With a 20 gallon tank that just means you have to put the fuel in jugs in the bed.
 

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Drive It Like Ya Stole It
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Discussion Starter #10
I rather carry jugs when I need them than sacrafice the bed space when I dont need it. Plus its weight, less weight is good sometimes.

Anyways I see in your plans that your roll axis is a 4 degree slope towards the front, is this axis always the slope of your upper links or no? Bear with me, im just figuring all of this out, ive been reading on PBB for many hours now!


Also how do you measure your COG, I havnt found a straight answer yet.
 

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We have some tubing from a previous project in our rack at work. I *think* it measures, 1 5/8" OD, 3/8" ID. The ID can be drilled and tapped for your link ends. Want me to get prices on it? It looks beefy as hell. Are you dead set on coil overs? I've had a few ideas about 4 links before but not sure if they could even be applied to an actual build up or not.
 

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Drive It Like Ya Stole It
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Discussion Starter #12
I was pretty set on coilovers, and now jason has cemented it. I was always going to run triple rates if I did do coilovers.

Is it DOM tubing? Can ya get the specs for me? Thing is this is probably a ways off. I need to pay back some debt, buy some tools and a few other things before I begin building up for this. Plus I want this to be a cut once project like Jason said. My SFA was pretty close to cut once because of all of the planning, I want this to execute in the same fashon - so lots of planning is in the future.
 

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Jason RIP
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Dark Eternal said:
I was pretty set on coilovers, and now jason has cemented it. I was always going to run triple rates if I did do coilovers.

Is it DOM tubing? Can ya get the specs for me? Thing is this is probably a ways off. I need to pay back some debt, buy some tools and a few other things before I begin building up for this. Plus I want this to be a cut once project like Jason said. My SFA was pretty close to cut once because of all of the planning, I want this to execute in the same fashon - so lots of planning is in the future.
Why don't you get a front driveshhaft on that thing first :lol:
 

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I'm pretrty sure its DOM but what ever you do, please don't go with aything less then .25 wall :imo If you wish, I can get you a price on some link material i'll garuntee for life :D :D
 

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I honestly dont think a 4 link is right for you at this point. When your truck is a trail rig, then a 4 link is the way to go. Yes it would be cool but at the same time, you will go mudding and get mud in the heims. Then to DD even if you clean your truck well there will still be mud in there and it will eat them up 2x as fast. IMO i think you should stick with what you got make a flexy leaf spung set up up front and enjoy it for a while, then buy another car and link the truck. It is your truck though and i wouldnt mind lending a hand if you did something like this, as long as it was dallas and not houston.
 

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Drive It Like Ya Stole It
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Discussion Starter #16
Eisenfaust said:
I honestly dont think a 4 link is right for you at this point. When your truck is a trail rig, then a 4 link is the way to go. Yes it would be cool but at the same time, you will go mudding and get mud in the heims. Then to DD even if you clean your truck well there will still be mud in there and it will eat them up 2x as fast. IMO i think you should stick with what you got make a flexy leaf spung set up up front and enjoy it for a while, then buy another car and link the truck. It is your truck though and i wouldnt mind lending a hand if you did something like this, as long as it was dallas and not houston.
Its not going to happen this month or even this year. I am aware of the trade off's and I dont DD my truck near as much as I used to. In fact it has traveled about 20 miles in the last 2 months :crazy:

Serisouly though, the ONLY time I use it now is when I need to haul or cant use my GF's car. I would probably just count on a new set of heims every year even with great care taken on them. Just regular mainanence.

BTW I dont know where it will happen, I need to see how my apartment complex handles me working on vehicles. Im thinking a lift instal will be fine, but not so sure about having a truck in the driveway half disasembled for a long period of time :crazy:
 

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Line-X of San Antonio
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Eisenfaust said:
I honestly dont think a 4 link is right for you at this point. When your truck is a trail rig, then a 4 link is the way to go. Yes it would be cool but at the same time, you will go mudding and get mud in the heims. Then to DD even if you clean your truck well there will still be mud in there and it will eat them up 2x as fast. IMO i think you should stick with what you got make a flexy leaf spung set up up front and enjoy it for a while, then buy another car and link the truck. It is your truck though and i wouldnt mind lending a hand if you did something like this, as long as it was dallas and not houston.
i was thinking something along the same lines. why would you link it for MUD? i personally dont think you need a link setup for what your trucks intended purpose is. but hey, its your rig dude. i would wait till you drive a beater or atleast have some kind of DD to get you around before you get goin on this.
 

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Finding COG

Good luck, it takes forever and a day, but it is essential for a correctly performing suspension.

Another thing, your going to have to seriously lower your truck to get a nice performing 4 link system without having the frame end mounts hanging way below the frame. The links can't run at too extreme an angle torwards the frame or this will induce alot of anti-squat so if your frame is way higher than the axle, your going to have brackets hanging way down.

And last but not least, something I left out of the origional post, once you get a good design, take some paper and draw the suspension at ride height with the pinion pointed in the correct location. Now draw the suspension in a compressed state and see where the pinion points. Then do the same with the suspension completely extended. It took me a few tries to get a good AS, a good RC, and a good IC while keeping the pinion pointed at the t-case at all times. If you watch my suspension my pinion never points anywhere but at the t-case so my axle end u-joint is always flat, never at any angle. This is accomplished by adjusting vertical seperation between upper and lower links at the frame and axle ends.

PS: I agree with above, you do not need a link suspension for mud. You do need it for a long travel application such as desert racing, or a high articulation sport such as rock crawling (why I did it). It's a whole lot of money and headaches and tradeoffs and not really worth it for mud.
 

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Would the things stated applie the same to the front of a truck or would there be differance. just trying to learn as much as possible since a sas is in my future and i wan't to link the front.
 

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Well thats a whole different can of worms. Ideally you want the instant center of the front and rear to be at the same location and you want the roll axis to be parallel (same plane if at all possible). Instead of antisquat you will have antidive in the front suspension. This is when braking forces applied to the axle housing try and keep the front end of the truck from diving. An ideal situation for street is to have enough AS in the rear to keep the rearend from squatting but not jack up the rear and enough AD in the front to keep the front from diving under braking. For rock crawling we tend to change these values a little since when we are climbing a smooth rock face and need some wheel speed we don't want the back end trying to crawl under the truck (too much AS) and we don't want the front end to be come light (too little AS) and we do want the front end to be pulled down by the acceleration forces on the front axle. It's all pretty complicated but once you get the general idea it's not too bad. I spent about 3 years researching before I built mine and about $400 on books on the subject. But I have a link suspension that works flawlessly and exactly how I planned...

Chassis Engineering Book: $30
Race Car Vehicle Dynamics Book: $100
Subscription to PBB: $25
Watching poorly built 4 links flip rigs upside down on trails while I cruise right on by without so much as lifting a tire: Priceless :D

Oh yeah thats another thing, with too high of AS and too low of a roll center I have seen trucks get the front tires wedged against a rock, driver accelerates and the rear axle walks under the truck but due to axle steer it turns and lifts one side more and the truck flops over, all on level ground without moving, pretty hilarious :anitoof:
 
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