Does anyone here have experience with air suspensions?

I'm building front and rear 4 links on my truck. The danm thing rides so harsh it's hurting my back.

I got a price on the bags, tank, lines, 2 compressors and Dakota Digital ride height controller ($800 by itself). Total comes out to $2,630. I don't like to buy the cheapest parts available, but does $2,630 sound reasonable?

Anyone know of a good source for components?

 

$2500-3000 is reasonable for a reasonably complete kit. No matter what kit you buy you will need fittings, maybe longer hoses, and so on.

I would also seriously consider acquiring four ball valves, four "T" fittings, and four shrader valves.

This way, should a line explode, or a tank split/leak/pop, you can close the valves on all four corners, and inflate with a tire pump just to get the truck off the asphault and home in one piece to repair.

While I've not installed "air" on my crewcab yet as I'm still accumulating parts (and have to get around to making bracketry), I did help a friend install air springs on all four corners of his 89 crewcab dually. The fronts went in just fine, essentially replacing the coils (4x2) and the rear required fabrication of a 4-link. We have the angles wrong but overall it's pretty good, and simply needs to be adjusted.

We used 3/8" plate for the brackets as he actually uses his truck quite hard.

 

that's a great idea with the ball valves, tees and the shraeder valves!

I did find another dealer that sells the bags that I want for $69 as opposed to $109 as quoted from the universal suspension ($2,630 quote). Looking at all the parts I need, I don't see how it adds up to $2,630. I'm convinced that if I shop around, I can save $500-1000. The trick is to not save money by buying tinker toy parts.

I'm hoping to buy all parst needed including shocks and steel stock for under $2,500.

 

Maybe a year or so ago I started researching the costs of adding an air suspension to my crewcab, and the range of pricing for kits (as few as their were at the time) was rather large. Anything from $1500 to $4500 depending how complete the kit was, or wasn't.

My crewcab is 2wd, so installing bags into the front is much easier to "fabricate", as replacing coil springs is fairly easy. I'd simply have to make a top, and bottom plate for the air bags, and install.

The rear is more complicated because the leaf springs provide more than just weight carrying functionality, they also locate the axle where it is. So fabrication will be required here.

For my friend's crewcab, we made a bunch of bracketry, and suspension arms. I didn't have my camera with me so I didn't take pictures. I'll be seeing him in a couple of months and if I remember I'll snap a few pics for you. But what we came up with wasn't rocket science. It's an old-school bracket racing 4-link suspension design fabricated out of really thick stuff.



As you can see the bracket is really nothing more than a "box" of heavy plate, with a piece of the bottom of the box extending under the frame. It's bolted to the frame, two bolts on the bottom, and four bolts on the side. The bracket mounting holes were drilled and tapped, so that the bolt heads are inside the frame, and the ends of the threaded part of the bolts hang into the bracket "just a hair". Eliminated the need for nuts. Obviously the right and left brackets are mirror images of each other. The bracket material is 4340N 3/8" plate. Gross overkill, but my buddy had some lying around and he can weld the stuff no problem.

Inside the "box" part of the bracket, are two 1" holes for installing two 1" rod ends in double sheer. The bolts for the rod ends go through the bracket on boths sides, through the rod ends, and through the frame with a huge 1" aircraft nut (interference nut) on the inside.

The four rod ends are threaded into the suspension links - which is 4340N tubing with machined 4340N threaded bushings on both ends - so the rod end (and jam nut). The bushings were pushed into the tubing (interference fit, took some beating), then welded to the tubing. Holes were drilled in the tubing ahead of time so eight plug welds could be done after the fact. This was done on both ends of the tubes.

The brackets for the rear axle were also fabricated, again, two plates per side with two holes per side for the two rod ends per side that are the same distance apart (in height) as the brackets in the front. Again, bolts in double sheer. He welded these brackets to his Sterling axle housing, after cutting/grinding off the leaf spring perches.

Then where the leaf spring perches were, brackets were made for the air bag mounts, as we made for the frame mounts to the side of the frame (with an underhang like with the front brackets), and the air bags inserted between and attached. We aired up all four corners with an air compressor as he hasn't done any of the plumbing yet. That's a project for another weekend. But the tentative diagram of what we're going to do is below:



He's still playing with different pressures to get a feel as to what is not enough or too much for the truck being loaded, unloaded, partially loaded, and the balance between front and rear.

The only thing we need to add to the plumbing are check valves before each of the 4-way valves so should the tank blow, both sides don't air down in a rude way.

Oh, and he built and installed a pan-rod to keep the axle from swaying left and right. Forgot to mention that.

My fabrication is essentially going to be the same thing, except out of mild steel because that is what I've collected The suspension links/tubes will be 4340N.

My buddy intends to buy the controller you were looking at, dakota digital. I'm thinking of making this an "experiment" and using an 8 analog input PIC chip, which will measure the pressure in the two tanks and the individual air bags, turn the compressor on and off as necessary, open and close the valves and such, based on ride height. This way the truck automatically "airs up" when I load her down, and "airs down" when I take everything out. Of course I'll have to do what my friend is doing now, and manually control the air pressure until i get a feel of what is appropriate for different loads, and also allow a manual override in case something gets wonky, or, my look up tables aren't correct.

The air compressor in my buddy's truck is a second air conditioning compressor - nothing fancy or official. He's almost done making the bracketry from my conversation with him last week.

Please excuse the fact I cannot draw.

 

For my 4 link rear suspension, I used all 1/4" mild steel. The links themselves are made out of 1/4" thick 1.5"x1.5" square tube. That's substantially heavier than it needs to be. I used 3/16" thick tempered pipe as the rod ends and installed regular leaf spring bushings from napa. I had to shorten them because I only wanted them to be 1.5" wide to achieve better articulation. Right now, I have two of the links installed as traction bars (works great ).

The Dakota digital controller seems like an easy solution to controlling the ride height. However, I don't see that I need a computer controlling the ride height. I may be mistaken, but I believe that the ride height sensors are simple 3 way switches with center position "off". When the switch gets pushed "up" it opens the air supply valve. When the switch moves down, it opens another valve that releases pressure from the bag. As I type this, I realize that I need 8 valves (one supply and blow off valve at each bag).

This would make for great cornering. As the truck goes around a corner, the suspension will pump itself up to correct ride height

Iirc, it's possible to control the ride height with the ride height sensors and a series of on/off pressure switches. From what I've been told, air pressure is not a very good way to control ride quality. I believe that all cars that come from the factory with air suspension have ride height controllers. I can't think of any that have a gauge on the dash that measures air pressure at the bag/strut.

I'm 99% positive that ride height can be controlled without a computer as described above.

yeah, your drawing sucks. lol just kidding. I'm rambling a bit here. I'm glad somebody else is doing this too .

 

I would not be opposed to a picture, or two.

Depends on the sensor. Some of the ride height sensors, like the Lincoln Town Car/Continental/whatever replaced the 90's continental use analog, variable resistors inside a plastic housing with a lever hanging off. Essentially it's a fuel-float sending unit more or less, as far as wiring. Then the air suspension monitors the resistance, to determine ride height.

Your suggestion, with an on-off-on switch, would work fine, except then your ride height is fixed. The advantage of the analog sensor, and a computer whether purchased or homebrew, allows you to adjust the ride height simply by changing the "go to this height" value in a table somewhere, and the computer compares that value to the sensor(s), then adjust accordingly. Most vehicles don't need something this complicated, but I want this "feature" for a couple of reasons. The drawback is complexity, additional coding since I'm making the computer from scratch, and of course, how to "average" the signals from the ride height sensors while the suspension is traveling on normal roadways, or offroad.

Yes, or four, four-way valves that do the same thing, in one housing.

Remember that springs handle the ride height in relationship to the load (including the vehicle's unsprung weight). Dampening is what help tames body role in corners. Stiffer shocks, sway bars, those sort of things. Remember the air in the air bags is compressible, hence how the air bag works as a spring.

I have a solution to the dampening issue as well - using rancho RS-whatever adjustable shocks, I and the same friend added three electrically controlled flow valves, between two manifolds. The shock goes to one manifold, the other manifold goes to the oil resevior. The three valves have different size orifaces, allowing different flow. More or less like binary = valve 1 has the smallest hole, valve 2 has a medium hole, valve 3 has a big hole. Combine closing of valves (or opening) for different combinations of dampening, Our system worked fine with toggle switches, and we installed it in an old Nova II. Stiffen for "corner carving" loosen it up a bit for daily driving, and make it silly loose in the front for drag racing and different dampening in the rear as well.

Anyway, I'm side tracking.

Except every time you hit a road irregularities, corner, or whatever, your switches are going to be actuated which while you drive down the road will cause the valves to open and close rapidly, thus changing your air pressure to often. This will ultimately result in vehicle oscillations that you would find unpleasant, not to mention dangerous. Ask me how I know this

It can be, but is it desirable? having been down this path before and put together a system (on the aforementioned nova II) you'll find it not to be a good thing.

I have a 2 page list of things I will be doing to my crewcab. I've crossed seven of them off so far.

I'm slow

 

I am not sure why my post disappeared, but I'll retype what I remember. Being brain dead isn't fun.

Anyway, what you suggest about the switch is a neat idea, however in practice it isn't going to work satisfactory, and here is why.

As you drive, the truck tires follow the road surface, even though the body/frame seem to float at a constant height. This is what the springs do. However, there is normal contraction and expansion of the suspension as you roll down the road, and a simple deflate-off-inflate switch will trigger refill and release of air almost constantly, unless the road is perfectly flat, there is no wind, and the truck is perfectly balanced.

That's never going to happen ;-)

So the OEM's (at least Ford) use a variable resistor type sensor, which works like a CTS sensor or a fuel level sensor - a voltage is applied to the sensor and read back off the variable resistor inside (indicating arm position, which connects to the suspension), and based on the *average* of the read values it determines ride height. Sampling the ride height once is bad because at the instant the sensor is read, you might be cresting a speed bump, or the tire sitting in the center of a pothole, that you just hit at 45 mph. That's why multiple readings occur and are averaged - to prevent constantly refill/release cycles which is hard on the compressor (which is not continuous duty BTW, at least in Ford vehicles), and of course wears out the valves fairly quickly.

BTW, I tried the switch idea as you suggested (two microswitches spaced apart with a wooden lever between them, wire tied to the rear axle) and attached 12V and two in-cab lightbulbs. Guess what happened? Blinkity-blinkity-blink-blink until I parked the truck and stopped moving.

Also, with a three position switch, you are forcing a certain ride height. That might be fine for an unloaded truck, but if you overload past what the swtiches can travel, something is going to break.

Trust me, you want some kind of averaging/sampling mechanism and some logic of some kind. It's how the OEM's do it. Caddy, Ford, Lincoln, and so on.

 

what you say makes good sense. I was wondering about the issue of bumps in the road. If the sensor is has a certain amount of play in it (to allow for most bumps in the road and some cycling of the air spring with out constantly trying to inflate/deflate) the idea still works.

As far as loading the truck so much that the sensor won't read anymore, something would already have to be broken, no? As you add weight, truck sinks down, ride height sensor calls for more air and truck is restored to normal ride height.

My thinking that the controller is the nicest way to go. But I'd still like to explore doing this with just the switches. If you've got 1/2" air line with 1/2" ports, you're going to bounce like hell if the sensors "blink" as in your experiment. 1/4" line wouldn't be as harsh, but it's still not good to have the valve cycling needlessly.

 

Well, try it and let me know how you like it

I didn't. But, maybe you'll figure out a better switch system than I did. I happen to like the OEM design... but you know that by now I'm sure!

Not necessarily. Depends what breaks first, the switch, or the suspension. Most switches have a limit of their travel, and if you don't want the switch to break, it needs to have the same flexibility as the travel of the suspension. Yet, you want it to trigger before your suspension is riding on the snubbers, or so high in the air the truck flips forward on the nose (exhaggeration, yes).

Well, skip the switches and electric valves, and use manual 4-way valves tied to the suspension linkage using an arm of some kind. Suspension moves up, air leaves the airbag. Suspension goes down, air enters the airbag.

I'd be interested in your results. having done this in an unhappy way, I am merely skeptical.

 

I'm only optimistic about the "brainless" ride height control because my cousin did it in his truck. He's over in Iceland, and he has since sold his truck. He's just finishing a 4 door s10 on 38" tires and air bags. I'll have to give him a call and find out how he did it. From what he explained to me about 10 years ago, there's a way to do it without the fancy controller. I'll post what I find out from him.

 

Please do, because my experience was the opposite, and I'm all for "cheap" solutions to everything

I would also be interested in seeing a picture or two of your current 4-link setup, if that's not to inconvienent for you.

 

I would be most interested in how he achieved this. I'm all for "brainless" controllers.

A side note: what's the chances of you snapping a picture or two of your four link, and sending them to me? I really want to see your work there.

 

well, here's a picture of one of the links. I have two of them installed as traction bars. It doesn't really show what my work looks like, and I shouldn't call it a 4 link yet....more like parts for a 4 link I just added some more pics to my gallery. Slightly better pics of "traction bars". Showing some rust, too.


and a couple of pics of the rig....