3-link (three link) w/air bag suspension questions

[1x1_Speed_Craig]

what pressure do you think you will run? empty vs loaded?

I have no idea at this point. With this specific trailer (and general weight) being new to me, I don't know what the baseline would be. I'll have to look at the recommended pressure range, and experiment with empty & loaded pressures.

Can you use a "sway bar" to control the roll?

I'm sure it could be done. I'd have to see how it handles without one.

The orientation of the shocks, providing I keep them as-is, should help with roll, also. They're mounted to the spring plates, and taper inward toward the center of the trailer (instead of angling toward the rear of the trailer).


Craig

 

[Martyn]

I have no idea at this point. With this specific trailer (and general weight) being new to me, I don't know what the baseline would be. I'll have to look at the recommended pressure range, and experiment with empty & loaded pressures.




I'm sure it could be done. I'd have to see how it handles without one.

The orientation of the shocks, providing I keep them as-is, should help with roll, also. They're mounted to the spring plates, and taper inward toward the center of the trailer (instead of angling toward the rear of the trailer).


Craig

Use ride height rather than pressure. The system will have to work with how you have loaded the trailer. If the left side is heavier than the right side the pressure will be different. As the air bag system has very low air volume the pressure differences can be quite large.

 

[bluejeep]

Your right they all bleed down over time and require the same maintenance as tires do. I guess I'm talking in degrees, these bags will stay inflated at the correct ride height for a week, rather than for an hour.
.

I used the simple 'push together' connectors and have no issues with leak-down during trips. Having said that, I do see leakdown while its stowed alongside the house over a month or 2 timeframe.
I included a pressure gauge inline with the tubing runs. It and the fill valve are on the trailer tongue. The airlines run inside the square tubing frame (installed AFTER welding please). I am adding a setup where I can connect lines that run into the cab of the tow vehicle to small airgauges on the dash (1 for each bag) so I can monitor pressure on the fly while towing. I run 80-95 psi loaded, and 20 psi empty.

 

[ntsqd]

The idea has been mentioned by a few people here, but I get the impression that I'd be the guinnea pig for actually trying it out.

"Nothing is impossible to those who don't know any better."
-- unkwn
"If we knew what we were doing we would not call it Research and Development."
-- A. Einstein
If you want to try it, I say go for it!
:sombrero:

Another impressive on-the-fly design. I lack the engineering background, so I'm still learning from you and others here. Thanks for the input.

Oh no, that's not an on-the-fly model at all. I flat-out cheated. That is a model left over from investigating various unusual or untried trailer suspension linkage concepts. All I did was grab it and make a few simple changes to get it to show what I wanted.

I find this comment interesting. I bought the M101A3 to save time, and it's a great set-up for my needs. At this point, a scratch-build frame isn't an option any longer. I guess I don't see how modifying this trailer would be that difficult or time-consuming relative to building one from scratch. Maybe you could enlighten me as to the compromises you might foresee.

The existing frame is all 'C'-channel. Adding linkage and air spring brackets to it forces localized boxing (at least) of the frame. Factor in that cross members may not be where they're needed or useful, any tongue mods necessary and you're going to have about the same and possibly more time in making the existing frame work. Look up diesel cruiserhead's trailer build thread. AIR Andre came to that conclusion near the end.

snip....
I originally had a Y shaped trailing bar to the middle of the axle much like the design shown in this thread. That worked well also. When I 'redid' my trailer tho I wound up with clearance issues between it and the trailer bed at full compression.

That has been a concern of mine. Depending on desired ride height and bump wheel travel needed this could be an issue. If the full length 2" socket tube shown in the jpg (for a loooonngggg adjustable tongue slider tube) isn't needed then it could be stopped at the last cross member ahead of the axle which would allow for about 2.5" more up travel.

The axle connects to the arms via std axle u-bolts. These arms go beneath the axle and extend past the axle to the rear where the bags sit on top of them. The top of the bags then connect to the trailer frame. Not exotic, but functional.

Essentially "Truck Trailing Arms", what Nextel/Winston Cup cars have used for rear suspension since the mid-late 60's. They place the spring in front of the axle, but the minor difference in motion ratio aside it's the same design. They use a track bar ('panhard bar"), but their lateral forces are huge in comparison.

Use ride height rather than pressure. The system will have to work with how you have loaded the trailer. If the left side is heavier than the right side the pressure will be different. As the air bag system has very low air volume the pressure differences can be quite large.

Some day I'd like to try using the ride height sensors used on some air ride cars with an air spring system. I have one such sensor from a GM car that my Grandad was going to use on his GMC MotorCoach's rear suspension air spring system. The load-leveling valves that it came with are known to have issues.

 

[Martyn]

Some day I'd like to try using the ride height sensors used on some air ride cars with an air spring system. I have one such sensor from a GM car that my Grandad was going to use on his GMC MotorCoach's rear suspension air spring system. The load-leveling valves that it came with are known to have issues.

We have looked into the ride height sensors. Off road they present some problems. Some of the sensors rely on a feeler or arm, these tend to get ripped off or bent. They also stop working when covered in mud.

The best set up we have come across is a military application where the sensor is sealed inside a two piece tube and uses a laser to detect changes in height. Until it can be mass produced its too expensive.

The other issue is the constant changes in ride height due to terrain. A sampling system is needed to average out the height over a period of time.

That said someone will come up with a solution and we'll be ready to use it when they do

 

[1x1_Speed_Craig]

Nope, not helpers. Full scale Firestone bags. I have a solid axle, with trailing arms going forward from the axle to the trailer frame. Each arm is roughly an H shape with the inner vertical being somewhat angled inward to resist lateral forces. That's instead of including a panhard bar. I originally had a Y shaped trailing bar to the middle of the axle much like the design shown in this thread. That worked well also. When I 'redid' my trailer tho I wound up with clearance issues between it and the trailer bed at full compression.

The axle connects to the arms via std axle u-bolts. These arms go beneath the axle and extend past the axle to the rear where the bags sit on top of them. The top of the bags then connect to the trailer frame. Not exotic, but functional.

Thanks for the explanation! :sombrero:

Essentially "Truck Trailing Arms", what Nextel/Winston Cup cars have used for rear suspension since the mid-late 60's. They place the spring in front of the axle, but the minor difference in motion ratio aside it's the same design. They use a track bar ('panhard bar"), but their lateral forces are huge in comparison.

ntsqd - Can you post up an image of this design? A couple quick Google image searches didn't really turn anything up for me.


I have seen a trailer air bag design posted here previously where there was a single arm on each side of the axle (looked like a ladder bar design), with a panhard bar. I'll have to do a search and see if I can turn it up again.

I want to keep the design simple, and again, keep in mind the intended use (95% on-road use).

Craig

EDIT: Something like this design...

 

[1x1_Speed_Craig]

The existing frame is all 'C'-channel. Adding linkage and air spring brackets to it forces localized boxing (at least) of the frame. Factor in that cross members may not be where they're needed or useful, any tongue mods necessary and you're going to have about the same and possibly more time in making the existing frame work. Look up diesel cruiserhead's trailer build thread. AIR Andre came to that conclusion near the end.

Who's AIR Andre? I tried to find his username, but had no luck. I'd like to read through his experiences.

I would definitely be doing local boxing if mounting to the C-channel frame rails, and would probably add a 2" x 4" box-section crossmember(s) to provide additional support, depending on the design. That, to me, seems much easier than starting from scratch.

Craig

 

[ntsqd]

snip....
A sampling system is needed to average out the height over a period of time.

I know this guy who....



AIR: "As I Recall"
try looking for "diesel cruiserhead" 's trailer build thread.

 

[1x1_Speed_Craig]

AIR: "As I Recall"
try looking for "diesel cruiserhead" 's trailer build thread.

Ha, ha...I completely didn't catch that. Yes, I have read through his thread (a few times) in great detail. I'll do so again tonight.

Having owned an M-416 before (which has a significantly lighter C-channel frame than the M101A2/3 trailers), I can see how he experienced the crossmember bending. It looks like the M101A3 has 5/32"-thick C-channel...substantial. Even so, I'd use box-section tubing for crossmembers to support air bag bracketry.


BTW, this is the other image/suspension design I was searching for previously (from THIS THREAD). It looks like a fairly straightforward design, and I'm wondering how it would work for my purposes.

 

[ntsqd]

For the rear axle of a tow rig or a trailer I much prefer some sort of converging linkage to using a panhard/track-bar design. My reasoning is that neither of these axles has a drag link whose arc of motion needs to be matched for bump-steer concerns and that any sort of lateral locating link causes lateral axle dislocation. That forces either the track width to be wider than necessary, or for a narrower than ideal body width for tire to body clearance. It may well be that the suspension's total range of motion isn't great enough for this to be a real problem, but the potential is there and I'd just rather avoid it altogether. If you do go down this path I would encourage you to make the panhard/track-bar as long as you possibly can, and then set it such that it slopes maybe 5* down towards the axle when at normal ride height. Try to put as much of the sweet spot in that arc as up-travel as is reasonably possible to do.

Could use a Watts Linkage to locate the axle, but the typical method results in one side having a very low anchoring pivot, and that won't work. So the variation that Matkins came up with of laying the plane of the links horizontal (@some point in the travel), but allowing the joints to work in 3D could work. Seems like a lot of complexity for a trailer and it would need to be in the region right over the axle, potentially limiting up travel or causing an excessively tall ride height.

A simple diagonal link, like used in some drag race ladder bar & 4-link rear suspensions, should be more than enough to keep the trailer's axle located. This could result in a very low Roll Center. I think an experiment might be needed to know how important this might be.

The thing that I don't like about the "truck trailing arm" or ladder bar designs is that they remove some of the suppleness that the air springs brought to the trailer. With two arms or links fixed to the axle a one-tire bump forces the axle to slightly twist in order to comply with the bump. That introduces a spring rate (the torsional spring rate of the axle) to that side's suspension. Since this is non-driven axle the only torque reaction needed in the design is for the brakes. Making one side rigid via a ladder bar type design or the trauck trailing arm's spring perch type design, but leaving the other side free to rotate at the axle will both resist the braking torque and remove the torsion spring effect caused by a one tire bump.

 

[1x1_Speed_Craig]

So, the stock leaf spring suspension is sounding better & better. :coffeedrink:

 

[ntsqd]

Do you like scrambled eggs?
:sombrero:

At some point I may convert the rubber torsion suspension under the TrailBlazer to independent. It will only happen if I run out of projects (extremely unlikely) or the current rubber torsion system fails. Were I starting from scratch I would probably go with that second design lay-out in my post above. Simple in design, simple to fab, lots of off the shelf components employable, none of the "ITS" alignment issues. I would try to put the air springs on top of the axle tube (no spring induced torsion), but it will work with them off the front or rear of the tube. About the only difference would be that the track-diagonal would go to the upper tube of the 'ladder bar" rather than the (easier to model) position shown on the lower tube. Really doesn't matter where it goes, just putting it on the upper gains a bit more clearance. I would put the frame pivot brackets on the front cross member and make the longitudinal links long enough to position the axle correctly. What I've shown in the pictures is a drag race ladder bar bracket turned upside down. I don't know that they will work (might be too tall), but I believe that they will.

 

[StumpXJ]

ive posted to several of the OP's threads, but here it is again. I use the "truck" or nascar style trailing arm setup. I have about 1800 miles of on and offroad pulling now on my trailer, and she pulls and handles like a dream. I would change absolutely nothing about the suspension at this point, which is NOT what I expected. I figured I would have to tweak a few things, but the very simple design works great on and off road.

I set my loaded ride height, and the PSI is usually at 45-50. It rides awesome like this, with regular oem style new chevy truck front shocks (they were short enough for my application).

The shocks are not in these pics, but you gte the gist of it. Aside from the cool and/or bling factor, there is no need (imho) for any more than a two link with a panhard. There is zero need for an upper AND lower link with the way the truck style trailing arm works. No expensive Johnny Joints, and extra tubing.

There is plenty of 'give' in the u-bolt/spring pad set up on the trailing arm to eliminate binding even though the COUPLER takes probably 95% of the twisting motion.

I used .250 wall 1.5 square DOM for the trailing arms, and 1.5 inch .180 for the panhard. Ballistic fab grease-able poly bushing on the trailing arm frame ends, and the same on the panhard ends.

Again, the shocks are not shown in these pics.

Good luck with whatever you decide, you have certainly had a lot options thrown out there to choose from.

 

[1x1_Speed_Craig]

ive posted to several of the OP's threads, but here it is again. I use the "truck" or nascar style trailing arm setup. I have about 1800 miles of on and offroad pulling now on my trailer, and she pulls and handles like a dream. I would change absolutely nothing about the suspension at this point, which is NOT what I expected. I figured I would have to tweak a few things, but the very simple design works great on and off road.

I set my loaded ride height, and the PSI is usually at 45-50. It rides awesome like this, with regular oem style new chevy truck front shocks (they were short enough for my application).

The shocks are not in these pics, but you gte the gist of it. Aside from the cool and/or bling factor, there is no need (imho) for any more than a two link with a panhard. There is zero need for an upper AND lower link with the way the truck style trailing arm works. No expensive Johnny Joints, and extra tubing.

There is plenty of 'give' in the u-bolt/spring pad set up on the trailing arm to eliminate binding even though the COUPLER takes probably 95% of the twisting motion.

I used .250 wall 1.5 square DOM for the trailing arms, and 1.5 inch .180 for the panhard. Ballistic fab grease-able poly bushing on the trailing arm frame ends, and the same on the panhard ends.

Again, the shocks are not shown in these pics.

Good luck with whatever you decide, you have certainly had a lot options thrown out there to choose from.

Stump - Thanks for the pics (again). That kind of simple set-up is appealing, and it's nice to hear that you're so happy with it.

I get dizzy and/or start rethinking things as I come across various peoples' builds. I definitely think your simple but effective set-up is within the grasps of wrapping my brain around (some of the other designs are probably quite effective, but make my head hurt :sombrero.

I'm going to search out your build thread, and read through it in detail.

Once again, thanks!
Craig

 

[jwiereng]

A good point was raised in this thread and worth repeating,most of the articulation of these types of trailers happens at the coupler.