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Discussion Starter · #1 ·
I'm building a 4 bar air ride rear suspension for my truck.

Its very tight fitting everything in. There is about 11.5 inches between the frame and the wheel with 265 tires to fit the air bag. When pressurized to 100 PSI the bag is 9 inches in diameter.

I plan to mount the center of the bag 5 inches away from the frame to leave 1/2" clearance between it and the frame and 2 inches of clearance between the tire.

Its not possible to mount the bag between the frame and the axle without lifting the truck. There is only 8 inches of clearance between the frame and the axle with the bump stop removed. About 6 inches with the bump stop in place. The shortest bags with any travel have a safe minimum height of 4" so that wouldn't leave much travel.

There is 10 inches of clearance between the frame and the perch on the back of my axle mount. One could get a shorter bag and mount it under the frame to the perch, but the bag volume would be so low that you'd have to run a ping tank in order to get the bag air volume up to get the ride quality up. Bags with 3/4" fittings suitable for use with ping tanks are more expensive and harder to get.

I've chosen a bag that has a low natural frequency for good ride quality. Its 13.5" high and that means it must go between the frame and the tire.

Bear with me... this is getting some where.

So... because things are tight between the frame and the wheel, I can't just bolt a plate with a bag mount onto the frame. I don't want there to be any material between the bag and the frame. And because the bag is tall, there isn't room for a bunch of bracing on top of the mount.

The bag mount has to be to the sides of the bag and down.

And this is all fine except that to mount the bag in this manner I pretty much had to move the axle back about 1.25 inches. The frame sides aren't perfectly flat and there are rivets and stuff and parts of the frame already look like swiss cheese so I don't want to be drilling a bunch more holes.

Like I said, I can make everything work if I move the axle back. I've posted pictures in my gallery so that everyone can see what I am talking about.

What does everyone think of doing this ?

The stock fenderwell space in front of the wheel and after it is about 4 and 5". I have about 5+ and 3.5+. There isn't going to be a clearance issue with these tires... but someday I might want to run 20s...

I haven't thoroughly checked my driveshaft yet. At first glance it seems OK. How much spline travel does the stock driveshaft setup have and how far out can one run them before they give trouble ?

I could shorten my bars and make a mount that would move the bag forward... but it would be a lot of work. What does everyone think of moving the axle back like I have ?

Thanks

Picture in my gallery here:

Air ride suspension pics - Me2000s Photo Gallery
 

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I notched and trussed the frame on mine, but mine is higher than stock by about 2" also. my bags sit right over the rear axle. I did this to be able to control the antisquat more with the bars than have the effects of the bags. I am running the 1t14c3 bag. I could probably get a better ride out of it with a ping tank but the bags have 1/4" ports in them iirc. on the driveshaft I do not know exactly how long the splines are but if you have already moved back 1.25" you will most likely need the shaft reworked there. I would keep the axle in the stock location and work on the frame.
 

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Discussion Starter · #3 ·
Are your bags inside the frame or between the frame and the tires ?

I was using 1T14C-7s (AON 5370). Same as yours but taller and more travel. Ride height is 13.5", natural frequency 64Hz or so.

As you see from the picture I was going behind the axle to get the bag volume up.

I did a bit of a redesign today and am now going with a 1TC15-1.5 (9422) and its going UNDER the frame BEHIND the axle. Ride height about 10.5 inches, 100 PSI diameter of 11 inches versus the 9 inches for the 5370s. I don't have the natural frequency, but I expect it to be in the 75 to 80 Hz range. I don't have a space problem anymore. Not as soft as the 5370s but should still be a lot better than stock. A couple more days of cutting, drilling, painting and installing and I'll be driving it.

I shortened my bars today. My diff rides in the stock location.

My bags have the 3/4" fine thread stud tapped for 1/4" NPT. I've called Firestone and complained about the lack of bags with the 3/4" NPT fittings. They might sell them at truck part prices instead of industrial prices. (3x more expensive)

If I ever need to hook up a ping tank, I am hoping to machine a fitting that goes from 3/4" NF to the air line and bore out the 1/4" NPT port to allow more flow.

This project is kicking my a$$... lots of measuring, designing, cutting, drilling, welding, etc. I can't wait to drive it when its done.

How does your truck ride compared to stock ? Did you air bag the front too ?

Is yours a 4 link ? How long are your arms and where are they mounted ? How bad is the antisquat ?
 

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my bars are centered under the frame rail right above the axle

its a parellel 4 link with the top bars 75% the length of the bottom bars for an instant center geometry.

ride quality from stock springs? no comparison. i would do it all over again in a heartbeat.

the front was bagged but on springs again, i was having too many issues with it. im getting a set of 05 axles and when they get here there will be quite a bit of redesign and the front will be bagged again.
 

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Discussion Starter · #5 ·
my bars are centered under the frame rail right above the axle
So those bags have a ride height of about 10". Stock = 8" + 2" lift ?

This air ride stuff is so much easier when the truck is lifted. Way more room.

its a parellel 4 link with the top bars 75% the length of the bottom bars for an instant center geometry.
That 75% thing is myth. It holds true for certain geometries but certainly not all. You could run the 4 link calculator to find out exactly what you have. I am going to have about 10% antisquat. I hope its not too much.

ride quality from stock springs? no comparison. i would do it all over again in a heartbeat.
What is what I wanted to hear. I'd love to know your bag number, ride height and inflation pressure so that I could see what your spring rate is and compare.

the front was bagged but on springs again, i was having too many issues with it.
I had one side of my front bagged for a few hours. The tire rubbed the bag when I turned it.

There is NO room between the front tire and the frame. Its even worse than the rear because the front tires turn.

I think I am going to build an air over hydraulic system for my front. 1.5" hydraulic cylinder in place of the spring connected via a hose to a 1.5" hydraulic cylinder pushed on by an air bag.

im getting a set of 05 axles and when they get here there will be quite a bit of redesign and the front will be bagged again.
Lets share what we learn about bagging these things.
 

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my antisquat is about 50% when i shortened the top links it made a big differnce in the way it handled I was really pleased with it after i did that.


With the 05 axle under there the 9" air spring will fit right where the coil used to be. I have seen a truck that kelderman did that they just built a adapter for it to fit in.

I usually run my bag at 9-10" I do not know what the pressure ends up being I dont have a pressure gauge on it. just have the regulator set at 95 psi, but i know there is not that much in it. Ill get that bag number tonight if i remember.
 

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Discussion Starter · #7 ·
my antisquat is about 50% when i shortened the top links it made a big differnce in the way it handled I was really pleased with it after i did that.
Your antisquat is pretty high. Does the back end rise a lot under acceleration ?
I'm at 94 to 108% depending on where I say the COG is. That is based on the numbers I am putting into the 4 link calculator.

The thing I don't like about a shorter top link is that it messes up the pinion angle as the axle travels. Its probably less noticeable on a lifted truck. It wouldn't take much for me to move my top mount and shorten my top link if I don't like what I have.

With the 05 axle under there the 9" air spring will fit right where the coil used to be. I have seen a truck that kelderman did that they just built a adapter for it to fit in.
Lifted trucks are SO much easier ! The extra 2-3 inches just makes all the difference.

I usually run my bag at 9-10" I do not know what the pressure ends up being I dont have a pressure gauge on it. just have the regulator set at 95 psi, but i know there is not that much in it. Ill get that bag number tonight if i remember.
OK. A 1T14C-3 (W01-358-5405) with a ride height of 10 inches has a spring rate of 280 lbs/inch (1.53 Hz) at 40 PSI and 1180 pounds and 356 lbs/in (1.39 Hz) at 60 PSI and 1810. Stock F250 springs are 320 pounds per inch but are probably much higher than that on the small bumps due to inter leaf stiction.

That should ride pretty good. And you still want to put a ping tank on it ? How do you find it compared to stock ?

Air spring spring rates are a bit misleading because they are SO progressive, especially with short bags. Its interesting to see your spring rates and hear that you would like it softer. Nobody would ever put a leaf on with a spring rate of 200 lbs per inch, but that sounds about right for the back end of a SD because as soon as it travels a bit, its up to 500 lbs/inch. The nice thing about air springs is that the spring rate increases when you put a load on them and if you want it higher you can just shut the valve on the ping tank. One could even install a high flow electric valve between the bag and the ping tank.

What are you using for shocks ?

Thanks for sharing/discussing. Any chance you have some pictures ?
 

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neat idea and alot of good info here, i would like to see the pics but they are locked out unless you are a member at that other place, Could you link the pictures here properly.

I have a dual bar setup on my truck (still running leafs) They are pretty much equal length and real long (go all the way up to under the cab (would these be too long to use in air suspension setup? I am assuming you are using something for a track bar as well?

Thanks Travis
 

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Discussion Starter · #9 ·
neat idea and alot of good info here, i would like to see the pics but they are locked out unless you are a member at that other place, Could you link the pictures here properly.
Ugghhh... (frustrated with these websites !) Yeah, I will when I get time. Or you could just sign up there too...

I have a dual bar setup on my truck (still running leafs) They are pretty much equal length and real long (go all the way up to under the cab (would these be too long to use in air suspension setup?
Depends on the strength and geometry. Google "4 link calculator", measure your truck and start playing around with things. Note: the link forces that the 4 link calculator determines are way high. I think they use a 6g load factor.

The closer the bars are together on your diff, the higher the force in them. My bars have 12 inches of separation on the axle. My lower bar will have about 8,000 pounds of force under the worst normal operating conditions (skid braking) with 6,000 pounds on the rear axle.

Some of the commercial 4 link kits for these trucks have silly small link separation on them. Like 6". Makes for really high forces in the bars... and their bars are not that strong. That makes me nervous, but maybe that is just me.

My links have more force on them because I mounted my bags behind the axle. The link force is less if you mount the bags directly on top of the axle, but there are room/travel issues if you aren't going to lift your truck. There are also problems using short bags... the shorter the bag the stiffer it is.

This sort of fabrication is not for the faint of heart. If your welds look like bubble gum or you don't know how to get good weld penetration, don't do this !

I am assuming you are using something for a track bar as well?
Yes, I will have a bar running behind the diff going from the frame to the other side of the diff. I am working on that today, as a matter of fact.
 

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travis, the longer your bars are too the more room for bar deflection you also have. i run a 32" bottom bar and a 25" top bar. I used 1.5" .250 dom mild steel tubing. like me2 said the calculator that triged from pirate4x4 has uses a 6g force which for street and mild to even medium offroad is WAY overkill. I have seen semi truck trailer links that are 1.5" .250 dom that are externally threaded for there end links, that is when i figured that if that link can survive 40,000lbs of trailer at skidding it can handle my truck. granted they have some more geometry advantages than my setup has by larger link seperation and there links are perfectly horizontal normally. My front will have 7" of seperation but thats the link seperation that is on the front axle thats how ford built it. also dodge runs 6.75" of seperation. also from the factory on the dodges there links are .125 wall rectangle hydro formed pieces. Fulltractions 4 link arms are made of 2" .250 wall so if i had to do it all over i would probably use 2" .250 but i have never bent a link. I think my biggest weakness would be if i put an external force on the link like getting stuck offroad. but even at the 6g calc it shows my links just at the edge of going to the undesireable range.

me2 where are you getting your information on the frequencies and spring rates?

oh yeah travis yeah i am running a bar perpendicular to the frame for axle placement. its 35" iirc the longer on this you can get within reason the better
 

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Discussion Starter · #13 ·
Fn = sqrt(spring rate/load)

An approximate spring rate is 1.38 x pressure x effective area / height. Pressure x effective area = load, so an approximate spring rate is 1.38 x load / height. The taller the bag the softer the spring.

The Firestone manual has more equations.

I got my system built with the new bags. I installed it on one side of the truck and I've been driving it around like that to check for issues. There are none. I'm going away for the weekend. I'll install the other side when I get back.

The 9422 bag at 10 inches is about the same spring rate as my F250 springs with the second longest leaf completely removed. (About 200 pounds per inch ?) Except that the bag handles the little bumps much better and its more stable as far as body lean is concerned. I'll report more once I get both sides working. I don't think I am going to need ping tanks. I might even have to add some fluid to my bags to firm them up a bit.

My Bilsteins aren't here yet and my stock shocks are shot.

My bars are 31 inches center to center. I used 2x2 x 0.250 mild steel square tubing.

The bar loads on highway tractors are different because the main spring is designed to take most of the load. It isn't the same as the 4 bar stuff we do. The bars you are speaking of are mainly for torque only. My bars wouldn't hold up the weight that a semi would put on them in my 4 bar configuration.

4 link setups, especially with the bag mounted behind the axle, put more force on the bars than do the semi type setups. That is why you never see a highway tractor with a true 4 bar setup. They always do something different.
 

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Discussion Starter · #14 ·
The F2107 looks just like the 5730. Same diameter, min height, etc.
 

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Discussion Starter · #15 ·
Jake: do you have stabilizer bar(s) on your truck ? I've got a feeling that I am going to need to add them to deal with roll issues.

When you run your design through the 4 link calculator, what does it say about roll ?

BTW: I don't seem to have any antisquat or dive. It seems to be bang on.
 

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Discussion Starter · #16 ·

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yeah when i built it there was not near enough know for pickups, i was experimenting!!

yes i run a 1.25" front and 1.125" shroeder sway bar there is very little with thoose bars

would a ping tank increase my travel? ill have to re run all my numbers in the calculator, i lost my old files on the old harddrive

i definately have learned alot over the years. when the 05 axles go under my truck theres gonna be some major design mods
 

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:ford:
yeah when i built it there was not near enough know for pickups, i was experimenting!!

yes i run a 1.25" front and 1.125" shroeder sway bar there is very little with thoose bars

would a ping tank increase my travel? ill have to re run all my numbers in the calculator, i lost my old files on the old harddrive

i definately have learned alot over the years. when the 05 axles go under my truck theres gonna be some major design mods
:evil:evil:evil:evil:evil:evil
 

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Discussion Starter · #19 ·
yeah when i built it there was not near enough know for pickups, i was experimenting!!
I am definitely not criticizing you. I just didn't know if you were aware and I didn't want to see you blow a bag from bottoming.

I know what you mean about the lack of info, at least for the DIY stuff. Yeah, there are kits but nobody really talks about them, until they fail. Not too many people building their own 4 link suspension for these trucks. 1/2 tons, yes. Not pulling/working trucks though.

yes i run a 1.25" front and 1.125" shroeder sway bar there is very little with thoose bars
Did you need them just for the bags or did you have them on before ?

would a ping tank increase my travel?
Nope. You'll either have to find a bag with a lower minimum height or notch your frame more or put the bags behind the axle like I did.

The minimum height is set by how high the bag will go and how high the piston goes into the bag.

ill have to re run all my numbers in the calculator, i lost my old files on the old harddrive
OK. I'll post my numbers when I get it all done.

i definately have learned alot over the years. when the 05 axles go under my truck theres gonna be some major design mods
I thought about doing this ever since I bought the truck, 10 years ago. This is actually my second attempt. My first attempt used Z leafs with the bags behind the axle. I didn't use a torque arm and every time I accelerated the bag end of my truck rose 6 inches. I kid you not.

I don't have that problem this time !

Where did you run your pan hard bar ? I was initially going to put it behind the axle, but I don't think I'll have room for the spare tire then. Its now going over the top of the diff.

Its great to have someone to talk to about this stuff...


BTW: the 2.5 to 3.5 inches of travel you have probably means that your bag volume is fairly low. You would get a softer ride with a bag that had more travel. My 9422s ride at 10 inches and have a minimum of 3.8 inches, giving me 6.2 inches of travel and lots of bag volume. I think the spring rate with them is perfect. I'll report back when I know more.
 

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oh i wasnt taking it wrong at all same thing here nice to have someone else working on this.

My dad has raced offroad so i know quite a bit about off road suspension so for me the 4 link wasnt too bad of a project.

yes i put the sway bars in afterwards. there actually out right now there is quite a bit of body roll but its manageable i am reworking some of the sway bar stuff right now. i have been running the bags about 11" lately, I will eventually try to get one with more travel but looking on firestones site there does not seem like there are many that have more than 10" from bottom to top. I have had my truck out on the ranch and beatin on it pretty hard and havent blown a bag, i figured if i was gonna have it happen it would have happened then. i do have bump stops that start to touch an inch and a half before the bag bottoms according to daystar the bumps should not let the bag bottom, and when i just set the truck down on them they compress about 3/4" I have the same bags that i was gonna use in the front, i should be able to pick up the travel if i run them up higher, when i had the rear at 9.5" was when i had the shatty leafs back on the front after taking off the links in the front, but now with the RSK and SD springs in front there about 11-12" soo many things to think about!! how much were your 9422's? they must have more bags than what they have on there website, i noticed truckspring.com has a TON of differnt ones.

Yes my panhard is behind the axle right now. above the axle is about the only place if your bags are behind. like you said with the z leafs i was afraid of having them behind the axle like a semi truck and having the lifting issue. that may be nice for a sled puller though! but having the bags in the back would keep the links loaded to one side. im using daystar's super flex rod ends. if i had to get new ones i would go with the ones from ballistic fabrications the spanner nut is a bit nicer, but when i did mine the ballistics were not out. it was the daystars, and jonny joints from currie.
 
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