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4 link air ride?

34K views 69 replies 10 participants last post by  powerlifter405 
#1 ·
looking at doing a 4 link air ride from airbagit. anyone have any experience with full air ride suspensions?
 
#2 ·
myself and me2 have the rear end linked and bagged, he is working on the front right now, and I will be reworking mine and doing the front this winter. I do not have any experience with airbagit mine is custom fab and so is his.
 
#3 ·
I would love to build my own but have heard some horror stories about angles and handling issues and possible other trouble. I am a millwright by trade and have alot of fab skills, just not sure on doing it myself.
 
#4 ·
Its easy to work out the geometry. Jake and I will help if you want to discuss things online. There is a thing called a 4 link calculator that makes it pretty easy if you want to get technical.

I don't like some things about the airbagit kit.
 
#5 ·
i would love to build it. need to design something. Truck is a daily driver, 4x4, and not looking to do any sort of lift, just have a better ride but still be able to haul stuff when needed. I have a 28ft fith wheel camper and a fifth wheel flatdeck trailer i use for my welding stuff. i also really enjoy and appreciate a custom mod. The four link set up from airbagit looks good and the bags look good but the bags appear to be mounted too far away from the original rear spring purches. This worrys me that the frame streangth for a bumper pull trailer may be compromised. i would also like to go with a self adjusting ride height like the big trucks.
 
#6 ·
There is a LONG thread on me2's build it sounds like what you are looking for the setup he has done would be ideal. Mine has about 4" lift on it. I have gusseted the frame on mine, but I don't pull off the receiver hitch often and when I do I am only around 5k. I have mine setup with solenoids and switches in the cab. This winter I am going to build some hall effect switches to give me some height feedback. The link calc is on pirate4x4 search for the user triaged it is his.
 
#7 ·
i am working from 5pm to 3 am (nights) and i can only use the computer during certain times of my shift. I am very interested in doing the front as well as the rear. The system i was looking at for self height adjustment would be similar to the big rigs. just a valve with a mechanical feedback rod attatched to the axle. I will try to find the write up and do some research. Where do you guys buy the parts from? link ends mostly, i guess everything else is manufactured. Thankx.....
 
#8 ·
i am working from 5pm to 3 am (nights) and i can only use the computer during certain times of my shift. I am very interested in doing the front as well as the rear.
My front air ride suspension is working well. And I'm working on an air ride cab suspension.

The system i was looking at for self height adjustment would be similar to the big rigs. just a valve with a mechanical feedback rod attatched to the axle.
Height control valves. Easy to set up.

I will try to find the write up and do some research. Where do you guys buy the parts from? link ends mostly, i guess everything else is manufactured
I made mine. I pressed RB155 rubber bushings into 2.5" 0.25" wall DOM tubing. I've been driving it for a year. I inspected the bushings this weekend and they are showing a small amount of deformation. I'm not sure if I should have used a harder bushing or not. I got my bushings at a HD truck shop. I buy most everything I use on my truck from HD truck shops.

All this stuff is in my threads.

Problem with air ride suspension... sort of... long - Powerstroke Nation

Air ride front suspension project - Powerstroke Nation
 
#9 ·
I am using Daystar poly swivel joints now, If I had to buy more I would get the Ballistic Fabrication ones. Well I just looked at the ballistic ones again and they have gone up in price and only have the forged ones but they are stout.
 
#10 ·
I'm leary of those sorts of joints for 2 reasons. 1) Wear. They are like ball joints. 'nuff said. 2) Zero vibration isolation. My truck got quieter when I put air ride on the back axle.

I don't think there is anything wrong with bushings. Manufacturers use rubber bushings in leaf springs and generally they last a long time.
 
#11 ·
On the wear issue my 6y/o ones are still almost as tight as new. But the vibration damping is very little. These are not metal on metal. there a spherical ball with urethane races on both sides. I want to look more into the rubber ones when I do the SD. I was thinking about using the ones that are on the front of the 05 axle for one end and the 3" ballistic joint on the other end of the bars.
 
#12 ·
I priced the front axle bushings. They were about $60 each at the dealer and I could not find an aftermarket substitute. It might also be hard to find a pipe that they press into. If you make them work, let us know.

I'm not sure that my bushings are wearing. I just noticed that the steel center of the bushing was more off center than what I thought it would be. They might just be more flexible than I thought. Everything seems smooth and tight. I am not having any issues.
 
#13 ·
#14 ·
That is one sweet ride. But not looking at doing any lift, just front and rear air ride. But it does give me some ideas.
 
#16 ·
looks like he does wonderfull work but i am not that rich and i would like the pride in doing my own if possible. Pretty well decided 2" dom tube with 2.5" dom on the ends with the pressed in leaf spring bushings. the goodyear bags 1R10-089 i believe. Just need to work out lenghts and such. My diesel weighs about 8500 lbs and i my fifth wheel camper is 10,000 lbs so i just want to be sure i do it right. Want to do stock height with 33" tires. any more reading and such would be great.
 
#17 ·
looks like he does wonderfull work but i am not that rich and i would like the pride in doing my own if possible. Pretty well decided 2" dom tube with 2.5" dom on the ends with the pressed in leaf spring bushings. the goodyear bags 1R10-089 i believe.
11R-089 if you are following my lead. You need a ride height of about 12 inches for a soft spring rate.

Just need to work out lenghts and such. My diesel weighs about 8500 lbs and i my fifth wheel camper is 10,000 lbs so i just want to be sure i do it right.
My 5er is about 13K.




Want to do stock height with 33" tires. any more reading and such would be great.
Stock height is way harder than lifted. When lifted there is lots of room for everything between the axle and the frame. Stock height means you really have to watch things, especially if you use a tall bag.

I'm running Ford 20" rims with 275/65R20 LRE tires. They are listed as a 34 inch tire.

Its doable if you want to do it. You need to be a good welder. It takes some time but it is so worth it.

Ask if you have questions.
 
#18 ·
ya looks good. my fifth is a keystone 28 1/2 foot sydney outback with 1 slide. and an 18 ft Tracker aluminuim bass boat to pull behind. Yes i am a good welder but i need some more information on the angles and bar lenghts and how the computer works. What type of weights would i put in my calculations? can i go with a little more refined look to the system like unequal lenght bars? I have read most of the posts i can find on the topic and am ready to start buying stuff but i feel i need a little more teaching on how the geometry works to fully understand how i can make it good for me. Thankx.... Do you know where else i might do some reading
? Thankx again....
 
#19 ·
Unequal length bars make it quite a bit harder to nail down the geometry. That introduces changes in pinion angle as the suspension cycles and roll-steer if the bars are not horizontal. It also means your anti-squat will change depending on ride height.

Look at fireman's pics of the PMF truck above and note the direction of the rear tires when the body rolls. That's called roll-oversteer when the back of the truck wants to swing wide when turning, whether or not that's bad depends on what you use it for and your driving style, most of my rock crawler buddies set their rigs up that way so the rear tires always land where the fronts do. It's just one more thing the 4-link calculator will calculate for you. As for the weights and measurements, I just went outside with a tape measure and measured everything the calc asked for, and the local landfill scale gave me the truck's weight. CoG is pretty hard, but the height of the top bellhousing bolts or cam is a decent start point.

I've been playing around with my geometry and have yet to get it where I want it. Equal length parallel bars is hard to beat if you're not concerned with having anti-squat, which for most people they wouldn't know the difference unless it was WAY wrong.
 
#20 ·
You must also take into account the travel of the bag and what amount of travel you plan on using. On the black truck pictured, that is fully aired up with no limiting strap (yes it should have had one for offroad situations like this one). The left bag is at approx 10" higher than the designed driving height. Its impossible to get a system to work the same throughout the entire suspension cycle. Its just a matter of getting it as close as possible at the design parameters of your use. If you need help, pm me, I will do what I can to assist.
 
#21 ·
wow great info. keep it comming. i was looking into maybe placing the lower bar equal to the centre of the axle and forward. the upper bar above and inline vertically with the axle. then the front end of both bars would/ could be placed a little closer and one in front of the other. I think i need some time working with the calculator. thankx so far guys....keep it comming.
 
#22 ·
Where to start, where to start...

Here is what governed me.

- I wanted the bars about 12" apart on the diff. The further they are apart, the lower the force in them. My bars see about 5,000 pounds of push/pull worst case, which is 6,000 pounds on the axle with tires skidding on really good pavement.

- I wanted to use a long travel bag for a low spring rate and a good ride. That means a ride height of 10 inches or more. That means the bag had to ride behind the axle.

- I wanted to retain nearly stock ride height. That means the axle must be able to touch the bump stop on the frame fully compressed, which means the top link on the axle must be within a few inches of the top of the axle or it will hit the underside of the box. (About 4" above center of the axle)

- Given the top axle mount must be close to the axle and the lower one must be 12" below it, its going to be about 8" below the center of the axle.

- I wanted the bars to be as long as possible to avoid as much bump steer as possible and to minimize anti squat.

- I wanted the bars to be parallel

- Given these two things, the furthest forward I could mount them was behind the rear cab mount. I went about 6" behind it.

- I put the top frame mount pretty much as high as possible and the lower frame mount 12" below it.

Once I got all this figured out, I ran the 4 link calculator and the numbers came out pretty good. I think I had 20% antisquat. In practice, the back end of the truck does not move up or down at all when braking or accelerating. To me this is paramount.

My bars are 31" long but should be an inch or two longer to better center the wheel in the wheel well. I under estimated how high I would run the suspension compared to where it ran with the sacked out leaf springs.

Hope this helps.
 
#23 ·
Where to start, where to start...

Here is what governed me.

- I wanted the bars about 12" apart on the diff. The further they are apart, the lower the force in them. My bars see about 5,000 pounds of push/pull worst case, which is 6,000 pounds on the axle with tires skidding on really good pavement.

- I wanted to use a long travel bag for a low spring rate and a good ride. That means a ride height of 10 inches or more. That means the bag had to ride behind the axle. I agree

- I wanted to retain nearly stock ride height. I agree That means the axle must be able to touch the bump stop on the frame fully compressed, which means the top link on the axle must be within a few inches of the top of the axle or it will hit the underside of the box. (About 4" above center of the axle) 4x4 may allow more room above i agree

- Given the top axle mount must be close to the axle and the lower one must be 12" below it, its going to be about 8" below the center of the axle.

- I wanted the bars to be as long as possible to avoid as much bump steer as possible and to minimize anti squat. This i didn't know but agree with
- I wanted the bars to be parallel This i am not too sure about

- Given these two things, the furthest forward I could mount them was behind the rear cab mount. I went about 6" behind it.

- I put the top frame mount pretty much as high as possible and the lower frame mount 12" below it. if i make bars unequal in lenght can i then shorten the distance and still keep strenght?

Once I got all this figured out, I ran the 4 link calculator and the numbers came out pretty good. I think I had 20% antisquat. In practice, the back end of the truck does not move up or down at all when braking or accelerating. To me this is paramount. This is also very good

My bars are 31" long but should be an inch or two longer to better center the wheel in the wheel well. I under estimated how high I would run the suspension compared to where it ran with the sacked out leaf springs.
This i will keep an eye on
Hope this helps.
Thankx a bunch. need to actually be with my truck and do some cyphering. I work construction and will be home in 2 weeks. want to buy some parts when home and try some measurements, but need to know what i am looking at when i get home.
Keep it comming if you can. Thankx....
 
#24 ·
i need to find some more info and training on how to use the calculator, just to ensure it will work. any help in finding info on how to understand the calculator and all the definitions? Please send a link or such for my reading. Thankx....
 
#25 ·
Although more expensive, it would be a good idea to make both the upper and lower arms adjustable. This will allow you to help center the axle within the wheel well aswell as alignment. Rule of thumb on spacing is 1" of spacing between the bars per 4" of tire. Making the links the length and angle of the driveshaft will allow everything to rotate on the same radius and prevent your driveshaft from coming apart/smashing into itself.
 
#26 ·
Although more expensive, it would be a good idea to make both the upper and lower arms adjustable. This will allow you to help center the axle within the wheel well aswell as alignment.
I don't think its necessary to make the links adjustable at all.

Rule of thumb on spacing is 1" of spacing between the bars per 4" of tire.
Maybe for a rock buggy. On a highway truck the torque rod is as high as possible on the diff so that it has the least amount of stress. If you are going to be hauling, I suggest spacing them apart as much as possible.

My rear axle has about 6K on it when I'm pulling my 5er. And I've had it floored in Lo pulling it up hills, etc. The forces are incredible.

Making the links the length and angle of the driveshaft will allow everything to rotate on the same radius and prevent your driveshaft from coming apart/smashing into itself.
The Superduty driveshafts have slip joints. When the rear diff is riding on leaf springs it DOES NOT follow the arc of the driveshaft from the carrier bearing. Its more important to get the anti squat and roll center stuff correct than it is to worry about the slip joint movement.
 
#27 ·
i think everyone has great ideas. Yes we have slipjoints, but i believe 99% of all vehicles do. 1 " per 4" of tire is a good rule, but is that for a gasser? my diesel is running 400hp and 800ft torque with a 8000 lb truck and 1/4 of the time pulling a trailer as heavy as the truck or more. Adjustable links are a really good idea, can be used for fine tuning of everything. Just my thoughts, more info on everything is great reading for everyone. Thankx..... Keep it comming.
 
#28 ·
me2 you mention antisquat and roll centre. the reading i have been doing says antisquat of 100% is perfect but what is meant by roll centre. Is there not more than 1 roll centre, and what are good numbers? thankx....
 
#29 ·
Roll center is complicated.

Best advice I can give you is to measure everything and then make your bars as long and flat as possible. Why ? For a given wheel deflection, the longer and flatter the bars are, the less the axle steers inward. Once you have everything measured, plug the numbers into the 4 link calculator and we'll discuss the results then.

The other thing is to put the air bags outward. Don't put them between the frame like they are on a HD truck. That works on a HD truck because they use partial leafs that act as a stabilizer bar.

The issue with adjustable bars is strength. You need a bar that can handle 5,000 lbs or more of compression load without bending. Generally a threaded rod is fine in tension. Compression is another thing. And they can't come loose.

The torque bars on a HD truck are adjustable. Some of the suspension kits use them. They aren't cheap and they aren't usually long enough and the ends don't allow much articulation. You could make up your own by threading pipe to accept the ends.

I had to cut the spring pads on my axles and weld them. That is how I set the pinion angle. If I didn't get it right, I was going to use shims to adjust it. All the HD truck shops have pad shims. Much more robust than adjustable links.

When I build something for my truck, I like to pattern it after how they do it on a HD truck. My GCW is over 20,000 pounds. I'm not going to fool around with designs and parts used on sprint cars and rock buggies. That is a different application altogether.
 
#30 ·
i just did some measuring on a truck of similar specs as mine. i think i will have about 10 inches between my tire and frame. Does this mean that the airbag will actually come up the outside of the frame? I am going to try to keep the bag about 1 inch from the tire and 1/4 inch from the frame and close to the backside of the axle. Yes the driveshaft angle is an issue and i will try to keep it as close to stock angles as possible. what lenght of travel, in the bags, do you need while you drive the truck. the truck will be set up to sit at about stock height, but when the suspention moves, during regular driving, what kind of travel can i expect in the bags. I have front and rear axle antisway bars. thankx...
 
#31 ·
i just did some measuring on a truck of similar specs as mine. i think i will have about 10 inches between my tire and frame. Does this mean that the airbag will actually come up the outside of the frame? I am going to try to keep the bag about 1 inch from the tire and 1/4 inch from the frame and close to the backside of the axle.
The 11R-089 is an 11 inch bag. The 5370 is 9 inches, but doesn't really have enough capacity. You need more than an inch between the bag and the tire and more than 1/4" between the bag and the frame.

What this means is that the bags need to go underneath the frame.

Yes the driveshaft angle is an issue and i will try to keep it as close to stock angles as possible. what lenght of travel, in the bags, do you need while you drive the truck.
For a good ride, you need an air column of 12 inches or more. For the 11R089, that means a ride height of 12"+.

the truck will be set up to sit at about stock height, but when the suspention moves, during regular driving, what kind of travel can i expect in the bags. I have front and rear axle antisway bars. thankx...
The 11R-089 has a minimum height of 4". The axle will touch the frame before it bottoms.
 
#32 ·
so at least the edge of the bag under the frame,and appropriate support. how far away from the tire should i run the bag? Is 2 inches or 3 inches right. How far will the bag actually extend if i wanted it to? the bag will only reach a certain pressure (this is a combination of dia of bag and weight of truck) then the bag will remain at that pressure and continue to raise truck untill it reaches end of stroke, CORRECT? but when additional weight is added to truck ride height will drop slightly and pressure will raise to compensate. Is this correct thinking? So when you say 12" of air column this is to absorb bumps and stuff while travelling and not allowing any bottoming out of suspension. New to this stuff and trying to get it figured out. Just typing it out and thinking i think it makes sense.
 
#33 ·
so at least the edge of the bag under the frame,and appropriate support.
Probably.

how far away from the tire should i run the bag? Is 2 inches or 3 inches
Something like that. You can't go by the static bag diameter because the bags get larger with increased pressure, like when you hit a bump.

How far will the bag actually extend if i wanted it to?
Height or diameter ? Its all in the bag data sheet.

the bag will only reach a certain pressure (this is a combination of dia of bag and weight of truck) then the bag will remain at that pressure and continue to raise truck untill it reaches end of stroke, CORRECT?
Nope.

2 things.

1) As you raise the bag from a position, the volume increases so the pressure drops thus the load it will carry drops

2) Most bags change effective area as they change height. Usually the higher the bag is, the less area it has.

Thus for any load and pressure there is a height. It confused me too at first.

but when additional weight is added to truck ride height will drop slightly and pressure will raise to compensate. Is this correct thinking?
Yep.

2 things give a bag its spring rate. The volume of the bag (versus its area), so really its height and how much the area changes as it changes height.

So when you say 12" of air column this is to absorb bumps and stuff while travelling and not allowing any bottoming out of suspension.
Not really. I say that to get a decent spring rate for a good ride frequency (1.5 Hz or less) you need a 12 inch column of air. In conjunction with a bag that doesn't have too much area change.

If the air column is shorter than this, the spring rate goes up and the ride ain't so nice.

The first bag I used was a 9422. I think the ride height was 10.5 or 11 inches. Sounds good, right ? Except that the bottom 5" of the height is taken up by the base. So the air column is only about 6". Its better than stock, but still a little firm.

The 11R089 bags are a bit taller than the 9422 and their base is hollow. Nice soft ride.

My front suspension uses a 7" bellow bag that doesn't have a whole lot of area change as it compresses. 7" by itself would be a bit too firm. So I bolted on a 5" accumulator. That makes it ride really nice.

Air bags are progressive. You can get away with a really soft spring rate because they firm up so nicely as the suspension travels.

New to this stuff and trying to get it figured out. Just typing it out and thinking i think it makes sense.
I went through everything you are going through and more. It takes a lot to design a good air suspension. Its way easier to ask questions now than to ask them after everything is welded together.

Did I mention that I am going to lower the bag mount on my axles 2" to get a taller ride height with my 11R-089s.

I was totally in the dark when I started my project. Luckily I thought enough of it through that it more or less worked the first time and it wasn't that hard to make changes to what didn't. (ie change from 9422 to 11R-089 bag, change ride height, etc.)
 
#34 ·
when i get mine worked out i will definetly be posting pics and such to help others as well. Thankx....
 
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