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Air ride front suspension project

61K views 58 replies 14 participants last post by  RJD 
#1 ·
I'm editing this post. DO NOT REPLY YET.

This is the build thread for putting air ride front suspension on my '99 F250 2WD Superduty.

For those not aware, I already have air ride rear suspension on this truck. You can read about it here:
Problem with air ride suspension... sort of... long - Powerstroke Nation

This is the 3rd front suspension that I'll be building for this truck

My 1st attempt used Firestone 5730 air bags. The problem with that setup was that there wasn't enough room between the tire and the frame for the bag. The 5730 bag has a ride height of 13.5" and a diameter of 9.1".

Here are some pictures from that attempt. Unfortunately, I don't have any with the bag installed. Trust me, everything was very tight clearance wise. I drove the truck around the neighborhood a few times without incident, but I wouldn't trust it for everyday use.













 
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#2 ·
The second suspension attempt involved replacing the '99 2WD coil buckets and springs with '05+ coil buckets and 4x4 springs.

The spring rate on the 2WD springs is really high. Like 672 lbs per inch each. 4x4 springs are much softer, 400 pounds per inch or less, depending on what spring you chose. I supplemented the 4x4 springs with coil bags from Firestone or Ride Rite so that I could adjust ride height a bit.

This setup worked OK in that it supported the truck. However, the lighter 4x4 springs were still a bit too stiff and I blew out a set of Firestone and Ride Rite coil bags after only a couple weeks of use. The 4x4 springs have since sagged quite a bit and pretty much need to be replaced.

Here are some pictures of this effort.









 
#3 ·
My present effort is going to use the Slam Specialties RE7 bag.

A data sheet on this bag can be found here:
http://www.slamspecialties.com/air_springs/RE-7.pdf

I emailed the manufacturer and they sent me a data sheet that included force versus height for a number of air pressures.

I chose the RE7 for a number of reasons.

1) Its a constant diameter bag. It doesn't get bigger as the pressure increases.

2) Its rated for a working air pressure of 200 PSI. This means I can use a smaller bag. Firestone bags, except the "Red" line, have a working pressure of 100 PSI max.

3) Its 7" in diameter. The 5370 was 9"+.

4) Its designed for "off axis operation"

5) It has a 1/2" diameter air port. Perfect for adding a ping tank.

While the RE7 doesn't have a constant force range like a rolling lobe 5370 bag does, its area doesn't increase very much compared to other bellowed bag. What this means is that with the use of a ping tank I can get a decent ride frequency. And its going to give a nice, progressive spring rate, something that is necessary and the front of my truck since it doesn't have much suspension travel.

My plan is to mount the RE7 in a similar manner to how I mounted the 5370s and add a ping tank above them.

The RE7s will be much easier to mount because the fit won't be nearly as tight and they are much shorter as well. The 5370s required every inch of available height under the fenderwell because they needed to be at a ride height of 13+" to be in their sweet spot. The RE7s have a travel range of 2.9 to 11 inches and their force curve is almost linear. I'll mount them with a ride height of 8 or 9 inches or so.
 
#4 ·
You can now reply to this thread. I can't go back to my first post and remove the "DO NOT REPLY YET" message. Moderators, help me !

Aside: why do posts become non editable at all ??????
 
#8 ·
Thanks.

But its really all about ride quality. I'm putting about 20K miles a year on my truck these days on long trips over roads that clearly need to be rebuilt. Lots of expansion joints/ broken pavement.

The rear suspension is great bordering on excellent on these roads. Now I need a front suspension to match.

It wasn't too bad with the 4x4 springs. Still a bit on the stiff side. Air springs are really progressive so I can shoot for a really soft spring rate for the first inch of travel and it will firm up as it soaks up the larger bumps. Coil springs can't do that.

I'll also be replacing the stock front shocks with Bilstien 5160s as soon as they are available.
 
#6 ·
Duh I just realized your is 2wd! I guess that is why I am thinking I am going to have some more room in the front for my setup. It is going to be spring time before I have money for wheels and tires so getting the 05 axles under my truck wont happen until then. But depending on your outcome I may link my current D60 and bag it until I can get my 05+ stuff all done the way I want it. I need to rework the rear end in mine still and build a setup for the SD rear end.
 
#7 ·
The 05+ 4WDs (ie coil spring fronts) and the 99+ 2WD SD front ends are pretty much the same as far as room is concerned. The 2WDs probably have more room because the steering knuckle is smaller.

The frame is the same. The track is the same. The tires are the same. I fail to see how a 4x4 would have more room.
 
#9 ·
Some math...

The stock spring rate on my truck was 726 pounds per inch. Source: 2000 Body Builder manual.

The front axle on my truck weighs about 4200 pounds.

f = pi * sqrt (springrate/load) = 3.14 x (726/2100) ^ 0.5 = 1.84 Hz.

The 4x4 spring setup used 2008 spring code X springs with a capacity of 4000 pounds and a spring rate of 355 pounds per inch.

f = pi * sqrt(355/2100) = 1.29 Hz. Better.

An 80s luxury car had a natural frequency of 1.0 Hz or so.

The spring rate of air in a cylinder (no area change as it compresses) is

K = 1.38 x Load/height

For a spring rate of 300 lbs per inch

Height = 1.38 x 2100 lbs/ 300 = 9.66 inches.

Spring rate in an air bag comes from 2 things. The air pressure increasing as the bag is compressed and the change in effective bag area as it compresses.

The RE7 bags increase in area a tiny bit as they compress, so I'll need an air column even higher than indicated by that formula.

If I mount the RE7s with a ride height of 9 inches and the upper and lower bag plates take up an inch between them, I'll have about an 8 inch column of air within them. I'll need to add a ping tank with about 3 inches of volume in it to get the spring rate I desire.

f = pi * sqrt(k/m) = 3.14 x (300/2100) = 1.18 Hz

For comparison, the rear suspension on my truck has a ride frequency of 1.3 to 1.5, depending on the load and the ride height. For a variety of reasons, the front suspension on a vehicle needs to be softer than the rear suspension or it feels weird.

I think the feel of the front end on my truck is going to change significantly with the tuned 5160s. My main complaint is that the pavement joints are very jarring to the cab and I think about 50% of that is due to the shocks transmitting the force to the frame.
 
#12 ·
I'll start tearing things apart and measuring tomorrow or Tuesday. I got derailed on other things and now I have to fix the rear brakes on my truck.
 
#15 ·
I tore things apart yesterday and started measuring. I'm waiting for some information from some vendors before I proceed further. Hopefully I hear back today.

This is what "we" are starting with. 2005+ spring bucket, 2005+ 4,000 pound 4x4 spring, Ride Rite coil bag, mounted on a '99 2WD frame. I never noticed the coil spring to be bent like that before. It might have something to do with the fact that I let the front suspension all the way down and then raised it again prior to taking the picture.


This is an RE7 bag set in place for reference purposes.


This is the coil spring and the RE7 bag side by side. The Slam bags DO NOT grow in diameter as they are pressured up. That is as big as it gets. The RE7 is pressurized to its ride height, which is 10" or so. The coil spring has an outside diameter of about 6".


Here is the coil spring, RE7 and a Firestone 5730 side by side. The 5730 WILL grow in diameter as its inflated. Its about 7" here, but when pressurized to 80PSI, its over 9 inches in diameter.


The 5730 has a ride height of about 13.5". The taller the bag the softer the ride. However, over 3 inches of that height is the piston, which doesn't hold any air. Thus the RE7 and 5730 has about the same "active" ride height. However, the RE7 increases in effective area as it is compressed, whereas the 5730 has a region where it does not. This makes for a lower spring rate. (Spring rate = increase in load due to pressure and due to increase in effective area.)

The 5730 and RE7 have about the same effective area and capacity. Its going to take about 75 PSI on the front of my truck. However, the RE7 is rated to run up to a nominal pressure of 200 PSI, whereas the 5730 is only rated to 100 PSI. Slam also makes an RE6, but they didn't recommend it for on the front of a Superduty.


After much deliberation and measuring, I am going to attempt to mount the RE7 within the stock spring bucket. Thanks to the fact the RE7 isn't supposed to expand as its inflated, it might work. Stay tuned. If it doesn't work, I have the airbag mounting towers from my first attempt to use as a starting point.


The spring rate on the RE7 is too high to be used by itself. I am presently working on connecting it to a base that increases its air capacity. I should have some answers in a couple days.
 
#18 ·
So... talked to Slam. They said one cannot drill the air bag mounting plates or the bag will leak. They also said you should not stack one bag on top of each other.

So... I'm going to build a 5" high x 6 5/8" diameter reservoir/base aka ping tank that sits between the airbag and the underside of the spring bucket.

The reservoir/base will have a hole in it sealed with an O Ring to allow air to move between it and the bag to lower the spring rate.

I'm CADing up the parts for cutting now. I hope they are done tonight.

This will be the first time I've ever welded on a pressure vessel...
 
#19 ·
Really like your work. That's something I would like to eventually do to my truck.
 
#20 ·
Why don't we see if it works before you say you like it ! :laugh:

The parts are cut. I'm off to get them.
 
#21 ·
OK, so I got a few hours to work on things tonight.

Here is the plate that is going to sit over the air bag. Its 3/8" thick mild steel.




This is how I am going to tighten the bolts INSIDE the accumulator to mount it on top of the bag. I'll seal the holes in the top plate with 1/4" NPT flush plugs. The other two holes are for mounting studs. All this will make sense when you see it go together as we go along.

The paint can is about the height of the accumulator. I'm using it so that you can see how this is going to work on the inside.


Here is how the O Ring seats on the air bag port. They didn't design that port to do this, but I think its going to work.


Time to remove the spring bucket AGAIN. I must have removed that thing about 20x already. I drilled out the rivets the first time I removed it and replaced them with 6 1/2" bolts. It seems to be a really solid way of mounting it. Nothing comes loose.


A lowly spring bucket. This came from a burnt 05+ truck. Its not the original bucket.


As nice as it is, the pipe extending from the top that holds the spring in place needs to be removed.




I love thin kerf cutoff wheels and angle grinders.



A sharp chisel works well.


Success ! Very little damage to the spring bucket.


Here is how the top accumulator plate will sit in the bucket. Its diameter is 6 5/8" Only a small amount of material on the edges of the plate need to be removed for it to sit totally flat in the bucket.


Here is how our accumulator and air spring will sit. The air spring is about 6.5" high here. It will have a ride height of 9". Remember that it will not grow in diameter when its pressured up. This is how it will sit under load.







Stay tuned for more to come tomorrow.
 
#22 ·
I got the passenger side of the front of the truck riding on the air bag. I didn't paint anything, the welds are ugly. I just wanted to get it working to see if it would work. And it does.

Here is what it looks like now.









Sorry about the quality of the pictures. It was dark out by the time I was done.
I've got pictures of all the steps in between, but until someone decides they are going to actually build something similar, I'll hold off posting them.

I've only got one side done. I drove it around for 20 minutes, hitting any bumps I could find with the left wheel. Here are my impressions.

The Good

Seems to ride really nice. I can tell the driver's side is harsher than the passenger side by a lot. The difference is pretty big, even with only one side done.

It doesn't collapse like a wet noodle going around corners. The soft coil springs do that. Lots of body lean. The air spring is much better in this regard.

Seems to be quieter. The back suspension was the same way. The truck got quieter when I got rid of the leaf springs.

There is good clearance between the bag/accumulator and the tire and the side of the tire will hit on the accumulator first, not on the airspring.

The only leak I had was with one of the 1/4 NPT fittings. The welds seem to be leak free and the O rings too. Everything worked ! I can't believe it ! I'll see if air leaks out when its parked overnight.

The Bad

It seems to take over 100 PSI to lift up the corner of the truck. The gauge on my compressor showed 120 PSI and the bag wasn't going higher. It might be the air chuck I was using. I'll look into it tomorrow. This won't necessarily be a problem as I will be using a 450IC compressor on the truck and it will put out 150 PSI if I need it.

The back of the truck feels rough now ! I know its way smoother than it used to be, but the front seems silky smooth now and the back is what does the biggest contribution to the roughness that still exists.

To soften up the rear axle all I have to do is increase the ride height and mess around with the shock damping. No big deal.

I am very happy that it works, especially that it worked so well on the first try. I was sure I was going to have problems with the O Rings or that the welds were going to leak.

I'll test it again tomorrow and see if I still feel the same way as tonight.
 
#23 ·
How am I going to weld the accumulator so that it looks nice ? I desperately need a rotator or something.

Or should I grind everything flush ?

This accumulator was just a prototype to test things with. I'll keep it as a spare. I want the next 2 to look nice. How ?
 
#24 ·
I feel your pain. When doing similar work I enlist the help of a friend or coworker to hold and turn the part. I'm also not againt grinding welds in a non-critical application such as this.

I'm watching intently because I'm going to go through the same ordeal pretty soon, right now I'm banging my head against my desk designing a 4-link with certain space contraints to allow a staged build but it's either not working or I'm over-analyzing it. When I was younger I would have just bought some material and started welding, and if it handled OK, I'm done. Now with the 4-link calculator I'm too worried about AS and IC and mostly wasting money on scrapped parts, lol.

What about ping tanks for the rear? Your using the goodyear bags in rear now, right?
 
#25 ·
I feel your pain. When doing similar work I enlist the help of a friend or coworker to hold and turn the part. I'm also not againt grinding welds in a non-critical application such as this.
It would be a piece of cake with a rotator and a MIG.

I'm watching intently because I'm going to go through the same ordeal pretty soon, right now I'm banging my head againt my desk designing a 4-link with certain space contraints to allow a staged build but it's either not working or I'm over-analyzing it.
Have you seen my other thread for the build on the rear axle ?

I had a h3ll of a time figuring out my rear suspension. Everything was tight. The key was getting the panhard bar over the rear axle and mounting the shocks outboard. Then there was room for the bags behind the axle and inward, under the frame.

I must have mulled about the rear suspension for 10 years.

When I was younger I would have just bought some material and started welding, and if it handled OK, I'm done.
That almost never works. I built a Z leaf suspension for the rear back in 2001. It was crap. Way too much squat and anti squat and the spring rate on the bags was too high.

Now with the 4-link calculator I'm too worried about AS and IC and mostly wasting money on scrapped parts, lol.
And wasted time. This is my 3rd attempt at a front suspension. I think I have something that works.

What about ping tanks for the rear? Your using the goodyear bags in rear now, right?
Yeah, I am using the Goodyears. They have hollow bases that hold lots of air and a nice big fat flat spot in the force curve.

I'm not using the Goodyear bags to their potential. I'm at the very bottom of the flat spot with the current bag height. I need to chop 2 inches off the beams that go aft of the axle. Then I'd be in the bag sweet spot. If I do that I don't need ping tanks.

BTW ping tank usefulness is quite limited due to the low air pressure my bags run at (~20 PSI) and the small port (/4" NPT) and the length of hose I'd need to the tank (2-3 feet).

To be useful, a ping tank needs a very low restriction route to the bag. I really like how I did the accumulator on the front suspension. The "hose" is 3/4" diameter and 3/8" long... though there is a port of sort protruding inside the bag itself.

The RE7s would have been too stiff without the accumulator. I'm very glad I did it that way. Some people don't understand that an air spring can be just as hard as a leaf spring if you don't work out the rate. That is how it was with my Z leaf attempt.

The only suspension that was worse than my Z leaf was when I took out first 1 and then 2 leafs from the stock spring pack. It was the worst riding truck ever. Incredibly bad.

I ramble like this thinking it might help someone... I hope it does.
 
#27 ·
I would mount the ping tanks like The talon setup if I had the need to:

Talon Air Ride
My shocks sit there, one on each side.

If you pick an air bag with a low natural frequency you won't need ping tanks. I spent a lot of time thinking about smaller bags + ping tank, versus bigger bags by themselves.

The Goodyears have a natural frequency approaching 1 Hz if you use them right. You don't want it any softer than that. Also, some of my problem is the shock valving I have. I'll be addressing that shortly.

I do not, however, know if their modified Z-leaf style link works worth a darn because I never found anyone who had it.
Zero axle articulation. A local suspension shop installed a couple and one broke the axle tube. I wouldn't do it.
 
#29 ·
What exactly are you hung up on ? What is the problem ?

What is stopping you from copying mine ? It works. I've been running it for a year with all sorts of loads, conditions, etc. Not a single problem. Just saying. Do what you want, but its a starting point.
 
#30 ·
Its nice to talk to people about these projects... I feel like I am out in outer space somewhere by myself when I'm working on them. I keep asking myself "Why am I doing this ? Oh yeah... so it rides nice and carries a load." You know its bad when you ask yourself the question AND answer it. :laughs:

I just checked my truck. The bag is still inflated. I'm shocked there are no leaks.
 
#33 ·
Its morning and the bag is still holding up the corner of my truck. Success.

I think I am going to pay a welding shop with a MIG and a rotator to weld the 2 accumulators I use on the truck.
 
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