spring shackle design question

[48Rob]

I'm working on a way to be able to adjust the chassis ride height of a trailer.
I don't want (can't afford) to do a hydraulic lift system, or a dedicated trailing arm airbag system.

The trailers dropped floor will be rather close to the ground at 7-8".
I'm trying to come up with a no tools-no locking brackets system to allow the trailer to ride low, or be raised either for clearance as needed, or to travel in the full up position if desired.

I've given up on the idea of dropping the chassis to, or very near the ground for garage door clearance, and have chosen to leave the chassis at a near normal ride height, and drop the floor further for additional headroom.
This requires however, that once the trailer is out of the garage, that the chassis be raised slightly, 2-3 inches.

The adjustable shackle link system is very simple, but would have to rely on a set of helper air bags to raise/lower the chassis.

The big question/unknown, is if the front leaf spring supports/leaf springs are strong enough to keep the axle indexed with the extra play additional shackle links will give?
The helper air bags will be attached to the axle and main frame at the center or just slightly behind axle center, and will provide all needed vertical strength, but will offer no sideways rigidity.
Running down a straight stretch of road isn't an issue, but cornering might be...
Current typical shackle setups offer the axle the opportunity for sideways movement during cornering, but I haven't been able to find any data that shows how much, or how much is allowed.

Rob

[KCStudly]

I don't think that would be very stable.

The air bag would be doing all of the work and the front portion of the leaf would merely be acting like a trailing arm link. At that point you might as well just do the air bag suspension with link (instead of leaf spring) and be done with it.

Also, on the rear shackle mount, you always want the eye of the mount to be a little bit forward of the eye of the spring. That way when the spring flattens it is always extending and the shackle can never invert (i.e. the shackle always points to the rear and down to some degree or another, never forward (with respect to down). If the shackle were to invert when the spring attempts to flatten it would then be trying to wedge the shackle hanger off of the frame (not good).

Now if you were to work out a way where your top shackle link was just a fixed part of the shackle hanger, and your middle shackle link had another pin/bolt hole in it and was extended some to the point that you could get a lever bar on the end of it, then you might be able to come up with an 'over toggle' arrangement where you could flip the toggle over and pin it in your driveway before you leave (so the middle link acts like a fixed link and the lower link acts like a normal single shackle arrangement). If that middle toggle had a center brace to strengthen the diagonal and a back stop so that the hole for the pin/bolt always lined up when it snaps into position, then you might have something workable (and cheaper than air bags).

If it were me, I'd do the air bags, trailing links and a Panhard bar, or just triangulated trailing arms w/o the bar.

[Dale M.]

There is probably no simple mechanical way.... Probably bite the bullet and use air bag (with trailing links and panhard bar - as mentioned above) or air shocks, that would be my route.......

Any other thing is just playing with more headaches and disasters.... The multi-linked shackel idea could work but you have to lock the 3 individual links to make it "1" at ride height and them means jacking up trailer and installing/removing some sort of locking pins each time you "change" height".... Seem like a system that will take lots of time and vulnerable to mechanical failure ( lost of or bent pins/locks)....

Dale

[Martiangod]

Hi Rob
Last thing you want is hydraulic, rides like a rock.
Few questions, how long are you leaves and how heavy is your trailer?

I would likely run air bags
I run them on my truck and they ride awesome, anyone who says they are rough or hard riding have too much air in them



or air shocks
Monroe makes great air shocks



The adjustability is going to depend greatly on the length of the springs, longer the better.
the double shackles would cause you a nightmare

Something I saw on a f450 was something like this

A swinging arm cross attached inside the frame, air bags controlling the rear shackle point.
would be fairley easy to make up a swinging shackle and using two air shocks to push it up, would ride good, shackle wouldn;t be any different in ride hight then a stock welded shackle point

rest hight


ride hight

I think due to the stiff nature of trailer springs, you would want to detune them some no matter what air route you go and let the air spring/shock work, possiblt monoleaf
In reality, in this config the air shock works as the shackle
Should be able to set a swiging shackle to give you any hight or low that you want or need

or build an air trailer
http://www.airtrailer.nl/motortrailers.php

Or the ultimate Timbren Dakota air suspension

http://www.timbren.com/air-suspensions.htm

[Martiangod]

Or loose the rear shackle, two cheapo shocks inboard of the frame angled to center the spring to act as a panhard

and bags





Oh and you said you were worried about cornering on air. Never install with a tee and one air valve, always use separate airlines for each side.
That way the air can't push to the inside airspring, and the trailer will stay level

And if you look at a mustang rear suspension pic, it would be fairly easy to replicate with air shocks and cut off springs and a sway bar from the wreckers

[48Rob]

Wow!

There's a lot of great ideas here.

Thanks to all!
It will take a bit to absorb all of them...

It looks like there isn't a great deal of side to side stress, if a set of air shocks would be enough to act as panhard bars with no rear shackles?

Under braking, the axle would want to roll rearward which would compress the springs/push the shackles back right?
If so, the front spring mounts will keep everything in order.
Since there is no powered reverse, movement the other direction is a non issue.
Even if there were, the spring shackles are the limiters.

If all that is true, couldn't the rear shackle mount be welded to a bar that went from side to side, and then be connected to a bar welded between the frame rails between which a lifting/lowering device was attached.
The lower bar would need side to side stops, and a vertical channel in which to slide.

Wish my drawing skills were better, I can see the picture clearly in my head, but attempts to put it on paper aren't working.

I like that pivoting shackle idea, I'll study that some more tonight.

Again, I've abandoned the idea of lifting/lowering the trailer 12-14" and have decided that 2-4 inches of lift/lowering will be plenty to meet my goal.

I definitely don't want a system of manually locking parts, and dealing with crawling around on the ground, it has to be simple and affordable.

I appreciate all the ideas and advice from everyone!

Rob

[eamarquardt]

Oh and you said you were worried about cornering on air. Never install with a tee and one air valve, always use separate airlines for each side.
That way the air can't push to the inside airspring, and the trailer will stay level.

Interesting thought! I put air bags inside the coil springs to level out the van when tongue weight is at max. Never thought about the air being shifted from one side to the other during a "roll". Have never noticed any difference in handling either. The instructions didn't mention anything about this issue. Perhaps the fact that the airbags aren't the primary spring makes a difference. Also it might be that the small line connecting the bags together is small enough to mitigate the effect (much as a baffle in a fuel or water tank does).

It would be easy to install a small valve in one of the lines so that the air bags can be filled/deflated to the same pressure at the same time and then one air line closed off to prevent transfer of air from one to the other during a turn.

Learn something new every day!

Cheers,

Gus

[Martiangod]

Air will definatly shift to the inside as the vehicle leans to the outside making tippage more likely.
And when your airing up, think how much a couple pounds makes to ride height, so if 5 pounds causes an inch lift, a 5 pound push to the inside will cause a 10 pound difference between sides.
Hence one side looses an inch ride height and the other side gains an inch, two inches difference from side to side, in a severe avoidance manuver you could theroretically push all your air to one side, setting up a rollover.
Another benefit to separate air valves is that if you have an uneven load, you can adjust that on your airsprings.

You ideal way to control sway with an adjustable suspension is a Watts Link instead of a panhard bar.
Anyone building a car with bags uses a watts link, keeps your travel even no matter what amount of air you put in, just think, if you track true at 15 pounds air, with a panhard, if you put more or less then 15 in, you will not be tracking straight
Fairly easy to build but make sure you use heim joints so you can adjust axel centering

[Martiangod]

Also it might be that the small line connecting the bags together is small enough to mitigate the effect (much as a baffle in a fuel or water tank does).

Cheers,

Gus

The small line actually amplifies the problem, the volume of air your dealing with in bags and airs shocks is very minimal, so a minute change has great effect

[Martiangod]

Wow!

It looks like there isn't a great deal of side to side stress, if a set of air shocks would be enough to act as panhard bars with no rear shackles?

Rob

there is side to side stress, but a gas shock or air shock will want to push back, see my new post about watts link, it solves all your centering and sway problems

[48Rob]

Thanks for the good ideas.
I'm still absorbing them all... while dreaming of camping in my new trailer...

Rob

[Martiangod]

Wow!

If all that is true, couldn't the rear shackle mount be welded to a bar that went from side to side, and then be connected to a bar welded between the frame rails between which a lifting/lowering device was attached.
The lower bar would need side to side stops, and a vertical channel in which to slide.

Hmmm, It could be done, its done all the time on some machines
Not sure if I'm envisioning what your asking correct or not



Beauty of my first rendition is its just 4 heavy L brackets bolted through the frame like shackles and a pair of shock mounts.
No side stops, nothing fancy.
Could put sleeves and brass bushings for the fulcrum, but I can't see needing any more


KISS
Although I like complicated too

It could be done, its done all the time on some machines

[48Rob]

Interesting!

I like your version too.

I was thinking square tube with the hanger brackets welded to the tube, and air bags between the two, but after looking at yours, a round rod, turned down at the ends to fit the spring eye would eliminate the brackets, and any need for shackles as the rod could turn in the spring eyes as the spring moved up and down in its arc.

Are those angle brackets as well, welded to the upper tube which rotates in a set of bushings, which keeps the springs from moving side to side?
Wouldn't the air shocks, bearing the full weight of the trailer, be very stiff?

In my minds version, the air bags would bear the full weight, in effect removing/over riding the function of the leaf springs, except for indexing the axle.
If the bags failed, the leaf springs would still allow the trailer to be towed, though much lower to the ground.

I'm still playing with your original idea, the one with the angle brackets, it does seem very simple...

Thanks for all the help!

Rob

[Martiangod]

Even simpler
Sub Frame
No Spring
Double convoluted bags
Spring perch on sub frame would have to be welded at ride angle to keep convex frame running true
shocks may keep it aligned, need shocks with bags
A Watts link may be needed though
Make one up with some tie rod ends





Probable shock angle, but mounted inboard the frame on each side



Sub frame would tuck right in behind your drop floor

Another thought I had is double wishbone out of a Ford Ranger 2 wheel drive, 5 x 4 1/2 bolt pattern. Disk brakes
Would actually be pretty easy to set up with bags
True independant suspension

[KCStudly]

Respectfully, some of these sketches look like spitballing that hasn't been thought thru fully.

The shock absorbers (be they air assist or not) are there to dampen the spring, not support it.

The subframe on the horseshoe subframe/air bag sketches would act like a giant rigid anti-sway bar transferring huge loads onto one hub or the other over irregular ground; you need some compliance in a 'solid' axle arrangement so that the wheels can articulate in a somewhat independent fashion.

The Ford Ranger front double swing arm arrangment would ride great, but would take up a bunch of inboard space.

None of these are easy, and I suspect none would be more cost effective then a simple air bag and trailing arm arrangment (assuming the OP is dead set on having an easy way to alter ride height to get into his garage).

I'm not a big fan of air shocks; they get stiffer as they go higher, which is kind of the oppisite of what I would want. Even air bags have there limits. Sure you can crank them up to change ride height, but for any given load they will ride best at a certain pressure, and that only occurs at one height; not necessarily the one you want it to be.

Hydraulics aren't rock hard if the hydraulic cylinder is used to alter the traditional spring mounting location and the traditional spring and shock are retained, but if you lower your ride so far that you are bouncing off of the frame rails, then...well, ya know...do-da-do, dupa dupa do-da-do, low-ri-der can't go too fast now.