Adding an air suspension to a Dexter axle

[Shadow Catcher]

I am one of those who like so many of you, can not leave well enough alone
One of the problems we ran into with Mega-Mini #1 is that there were a number of occasions where we dragged the rear a bit. Subsequent MM's will have three more inches of ground clearance, however...
I do not intend to do any serious rock crawling however we do plan on boondocking and there are times I will want more ground clearance. The Dexter axle has a reputation of being extremely well designed however it reportedly does not do particularly well on washboard.
How to get more height when you want it with a Dexter axle?
Some Times it IS Rocket Science

I gathered a good bit of information on air suspensions and discussed it with my brother-in-law, John, who is a mechanical engineer who has worked in aerospace (jet engines) and automotive, race car design and is an expert with one of the rather esoteric computer programs used for stress analysis. My experience includes failure analysis and non destructive testing including the space shuttle to carnival ride inspection.
To cut to the chase.
The design is finalized and work started on the prototype, the CNC is finished on the bracket attached to the arm and a pair machined out of aluminum. The prototype air shocks will be those used in a Corvette


early design, note final product has only three holes for mounting shock.

Shock support arm attached to axle final design



Machining




Final bracket


This BTW is all being done in John's home work shop

[01Sport]

Looks good.

[schaney]

My initial thought is your air-shock approach on a rubber-band axle will give you some lift but at the cost of reducing travel and notably increasing your effective spring rate. This is because your air-shock will be working against the torsion action of the axle to gain lift.

[Shadow Catcher]

One of the ideas was to negatively load the axle and take the load on the air shock. The Torflex axle reportedly does not handle washboard well because it is too slow to respond, this hopefully will address that.
The height difference will not be huge, the shock itself will give you a four to five inch difference and which of the three holes you attach the bottom of the shock absorber will affect the angle and loading. There are certain aspects of this that can not be computer modeled as we do not know what the spring rates... for the Torflex are? Once I have the new MM with air shocks installed I will be in search of some washboard road, and we will try various air pressures and attachment positions on the lower bracket. I dug out my video camera yesterday. The Dana test track is not far from where I live, but I would bet they wants lots of $ to use it.

Progress

[bobhenry]

OK I'll be the dumb ass what goes to what. Where is the frame and the shock and how does all this mount? Looks like you are stiffining up the ride to me by pre loading the torsion arm. Would it not be as easy to raise and lower the entire torsion axle to change the ride height with a frame hinged assembly to mount the axle on???

I'm lost

[aggie79]

I think I have figured out what goes to what, but this raises a few questions:

1. Will there be enough clearance between the shock and tire/wheel given the spindle length of the Dexter?

2. Wouldn't a traditional leaf spring, drop axle suspension with shock absorbers do the same thing for less complexity and cost? (Athough you can't beat the coolness factor of your design.)

Tom

[schaney]

As I understand it rubber-band axles have a couple of issue when used off-road. First, as noted, the design is too slow in responding to washboard conditions so it bounces over instead of absorts the bumb. The second problem is dust and dirt. The ends of the beam aren't sealed, as dust and dirt get in, this cause friction and heat. This causes the rubber inserts to work loose, ultimately causing a failure of the drop arm. (Info from Adventure Trailers Suspension Design)

My assumption is, there will be a very small window of travel, where you can "unload" the axle and have your air shock carrying the load. Will be an interesting experiment to see what happens.

On the cool factor, the brackets do look nice.

Tom, a traditional leaf spring setup has complexity and is serviceable in the field if something breaks but not cheaper. You need to use automotive grade springs to create a decent setup that can absorb washboard conditions. This off-road frame I build has about $450 in the springs, hanger, shock, bushings. That's wholesale cost and does not include the axle cost, althought it does great in washboard conditions.

[Shadow Catcher]

I should have the completed product at the end of next week and will mount it to the rolling chassis.

The intent is not an all out boonie basher but a additional lift when you need more ground clearance wile not sacrificing road handling or adding height when you are not off road.

"Where is the frame and the shock and how does all this mount?"
T) This mounts entirely on the Dexter Axle. Note that the curvature of the bracket follows very closely that of the axle tube and will be held on to the tube with a flat custom bent U bolt. the two brackets are held on with stock U bolts
"Looks like you are stiffining up the ride to me by pre loading the torsion arm. Would it not be as easy to raise and lower the entire torsion axle to change the ride height with a frame hinged assembly to mount the axle on?"
T) This unloads the Torflex placing the load on the air shocks. The additional air bag (as you describe) is the approach taken in Dexter's VERY heavy duty axle and yes you could, but again this adds levels of complication and height and weight. We wanted this to be a bolt on kit that any one could install on an existing trailer with no welding...

"Will there be enough clearance between the shock and tire/wheel given the spindle length of the Dexter?"
T) I can't tell you how many times I crawled under the MM and or took off a wheel to get exact measurements. I had to replace my digital caliper (dead after 20+years) to get dead on accuracy. The shock was carefully chosen and you can see the steps cut into the brackets to make it all fit.

2. Wouldn't a traditional leaf spring, drop axle suspension with shock absorbers do the same thing for less complexity and cost? (Athough you can't beat the coolness factor of your design.)
T) But does not give you independent suspension something the true boonie bashers do have. The trailing arm suspension has some advantages off road as the wheel moves back and up when it encounters a bump. There is also a lower center clearance with a conventional axle. i.e. My Subaru Outback has about the same ground clearance as a conventional Jeep, because the low point on the Jeep is the differentials and the Subaru has a symmetrical independent suspension.

There is very little space between the arm and the ends of the axle tube (I know I tried to measure it) and I am thinking there may be a way to seal that up some, pipe cleaners, O ring, silicone grease or caulk (does not attack rubber)?

[High Desert]

so Shadow Catcher, is this just for the fun of designing, or do you have possible bigger plans for this? It looks like a very slick setup, even if a person just wanted to add regular shocks instead of air shocks like the original intent of your design. You guys are doing some nice work.

[Shadow Catcher]

The hope is to come up with something marketable, and besides I was frustrated and I want one
I would have carved something out of a steel plate modeled after the one that Monroe had if all else failed, but they stopped making it, and I had to wonder why, my bet was liability. The way it was designed it bolted to the frame (you had to drill the holes) and you had better have a very substantial chunk of metal to bolt through.
My brother-in-law is very good and I know he has done a good bit of design for Nascar and Formula 1 teams, they would send him a part and say make it stronger and lighter.

[vrodjason]

Looks like a 3 or 4 link setup with air bags or air shocks could be another good way to go. They are fairly simple to build. I built one to go under my old '67 Galaxy. A local spring shop here sells all kinds of the ends needed for the link arms. Just an idea. Would be pretty cool to pull in a camp site, unhook the td, flip a switch and lay the frame almost to the ground. Thinkin of building a rat rod for a tv this would give it even more of a cool factor.

[Shadow Catcher]

Final kit for testing

[danlott]

I don't really know if these are needed or not, but the machining and design are cool. Looking forward to the install photos and performance reports.

Dan

[Shadow Catcher]

This is the first mounting. the U-Bolts need to be trimmed and I did not get the correct bolt for the attachment of the Shock to the upper bracket.
One major concern, I did not take into account the clearance when used with brakes, which the next MM will have.
Does any one know the clearance between the Torflex arm and the back of the brake plate?

[schaney]

Hmmm, no dimensions for the brakes in their catalog, the hyd brakes have a flat backing plate and the elec ones wrap around the backing plate. Try calling Dexter.