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| [GMCnet] Rear suspension air bag comparison [message #224141] |
Mon, 30 September 2013 19:36  |
BobDunahugh
Messages: 2465
Registered: October 2010
Location: Cedar Rapids, IA
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I put Jim K's Quad bag system on the 78 that I sold to a friend. I then drove it 220 miles to his house in Wis. It seemed to have vary little sway at the rear. The ride seemed to be about the same. I thought the unit was strong. Easy to install. And well made. I do like the idea of not totally depending on one bag on each side. If you had a total bag blow out. I think that the coach would be more controllable at speed with Jim's set up. I'm putting one on my 78 along with 4 rear disc shortly.
Bob Dunahugh78 Royale
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| Re: [GMCnet] Rear suspension air bag comparison [message #224199 is a reply to message #224188] |
Tue, 01 October 2013 13:02  |
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From the engineering aspect, the front wheels of the system will take the
full brunt of a bump. It has no capability of transferring the necessary
lift through the bogie (as designed) to the rear in the "Q-bag" system since
the point where the bags meet is stationary.
Yes, the "Q-bag" is firmer and has little sway. If you tow an Olds
Silhouette then this system is ideal. If you want what was designed and
tested from GMC then go with something very similar to the original design.
On either system, if you loose a bag you loose the ability to travel. Yes,
there are stories about some limping home with "limping" being the operative
word. You can't limp at 60 mph and not put additional strain on the tire
taking the full weight of that side and risking not only a bag blow out but
a tire blow out.
So, the question is this. How much is a blow out to you -- bag or tire?
Choose your poison or, if you prefer, choose your gun. The wound will be
self-inflicted regardless.
This leads me to something else. Bags seldom develop leaks. More often they
go all at once. Tires, however, may go more slowly though the rapid failure
and blowout risk still exists.
Byron Songer
Louisville, KY
Sigmund Frankenfelter wrote:
>
>
> While I can understand the theoretical aspect of having six wheel independent
> suspension, and I do understand the convenience of not losing an entire side
> when one tire blows, I keep coming back to an engineering concept.
>
> The vehicle was not built for that kind of suspension. This necessarily means
> that, when installed, the chassis and other structural components are going to
> be under stresses that were not designed in by GM.
>
> I keep asking myself "what unexpected thing is going to fail"?Of course I'm
> not an engineer,and that may be why I can't find a flaw in this concern.
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Byron Songer
Full-timing to enjoy the USA
Former owner but still an admirer
GMC paint schemes at -
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| Re: [GMCnet] Rear suspension air bag comparison [message #224204 is a reply to message #224188] |
Tue, 01 October 2013 13:52 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Sigmund,
Here' my take on how the force of hitting a bump or pothole is transferred. When the middle wheel hits a pot hole the force is
transmitted through the bogie arm to the air bag arm. The air bag arm transmits the force to the air bag. The air bag transmits the
force to the Q-Bag frame. The Q-Bag frame transmits the force to the two 1 1/4" OD bogie pivots and the four 7/16' diameter bogie
box bolts.
That sequence is repeated when the rear wheel hits the pot hole.
Experience has shown that the components listed above are up to the task. The bogie arms don't bend, the air bag arms don't bend,
the air bags don't explode, the Q-Bag frame does not bend, the bogie pivot points and mounting bolts don't shear.
I'd guess that the weak link in the entire system is the air bag and I've never heard of one bursting when hitting a bump or pot
hole.
Regards,
Rob M.
-----Original Message-----
From: Sigmund Frankenfelter
While I can understand the theoretical aspect of having six wheel independent suspension, and I do understand the convenience of not
losing an entire side when one tire blows, I keep coming back to an engineering concept.
The vehicle was not built for that kind of suspension. This necessarily means that, when installed, the chassis and other structural
components are going to be under stresses that were not designed in by GM.
I keep asking myself "what unexpected thing is going to fail"?Of course I'm not an engineer,and that may be why I can't find a flaw
in this concern.
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Rear suspension air bag comparison [message #224221 is a reply to message #224215] |
Tue, 01 October 2013 15:47 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Sigmund,
The "big leverage" is being applied to the frame fore and aft by the Q-Bag, The chassis frame is a "C" channel six inches tall and
~1/8' thick; I can assure you that chances of the Q-Bag applying a force great enough to damage the frame is virtually non existent.
Like I noted in my first message the "weak" point in the system is the air bag.
Regards,
Rob M.
-----Original Message-----
From: Sigmund Frankenfelter
It's the only reason I went with Sully's system - the forces on all of the structural parts of my coach end up basically identical
to stock.
I am glad that the quads are working for people, and they do look substantial. But when I look at pictures of an installation, I see
big leverage being applied to the chassis. Now maybe the GMC engineers were planning ahead for six wheel independent suspension, but
I have never read anything that indicated that.
I am not trying to justify my own purchase. I simply looked at the stock suspension, saw how it worked, and got nervous about it
working so differently. That's the reason I went the way I did.
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Rear suspension air bag comparison [message #224231 is a reply to message #224221] |
Tue, 01 October 2013 18:03 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| Robert Mueller wrote on Tue, 01 October 2013 16:47 |
Sigmund,
The "big leverage" is being applied to the frame fore and aft by the Q-Bag, The chassis frame is a "C" channel six inches tall and ~1/8' thick; I can assure you that chances of the Q-Bag applying a force great enough to damage the frame is virtually non existent.
Like I noted in my first message the "weak" point in the system is the air bag.
Regards,
Rob M.
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Rob,
I will not dispute the above as a single line, but what you and others have not considered is the moment that the bogie bracket now applies to that frame rail that now happens twice with each road surface irregularity as a long term fatigue load. While I am not asserting that this will result in a failure of the frame rail, I see it as less than ideal in view of the number of frame rails that have failed due to corrosion.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] Rear suspension air bag comparison [message #224238 is a reply to message #224231] |
Tue, 01 October 2013 18:10 |
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USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
Karma: 6
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Senior Member |
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Matt,
I agree, I've seen a number of frame rails on which the area just behind the bogies is paper thin and AFAIK all bets are off in that
situation.
Regards,
Rob M.
-----Original Message-----
From: Matt Colie
Rob,
I will not dispute the above as a single line, but what you and others have not considered is the moment that the bogie bracket now
applies to that frame rail that now happens twice with each road surface irregularity as a long term fatigue load. While I am not
asserting that this will result in a failure of the frame rail, I see it as less than ideal in view of the number of frame rails
that have failed due to corrosion.
Matt
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Regards,
Rob M. (USAussie)
The Pedantic Mechanic
Sydney, Australia
'75 Avion - AUS - The Blue Streak TZE365V100428
'75 Avion - USA - Double Trouble TZE365V100426
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| Re: [GMCnet] Rear suspension air bag comparison [message #224260 is a reply to message #224238] |
Tue, 01 October 2013 19:19 |
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And it all defeats the purpose of the original design. I'm with Sigmund.
Try driving a multi-bag rear end with stabilizer between the bags over
several 4x4's and then drive the OEM over the same course. You'll find out
what the difference is rather quickly, I imagine. Especially if you're
observing from the outside. BTW, if your seat is sensitive, you'll feel the
difference inside, too.
A real-world test would be to take a speed bump at 35.
Say, is this like the best kind of tires or what?
Byron Songer
Louisville, KY
Rob Mueller wrote:
> Matt,
>
> I agree, I've seen a number of frame rails on which the area just behind the
> bogies is paper thin and AFAIK all bets are off in that
> situation.
>
> Regards,
> Rob M.
>
> -----Original Message-----
> From: Matt Colie
>
> Rob,
>
> I will not dispute the above as a single line, but what you and others have
> not considered is the moment that the bogie bracket now
> applies to that frame rail that now happens twice with each road surface
> irregularity as a long term fatigue load. While I am not
> asserting that this will result in a failure of the frame rail, I see it as
> less than ideal in view of the number of frame rails
> that have failed due to corrosion.
>
> Matt
>
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Byron Songer
Full-timing to enjoy the USA
Former owner but still an admirer
GMC paint schemes at -
http://www.songerconsulting.net
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| Re: [GMCnet] Rear suspension air bag comparison [message #224265 is a reply to message #224260] |
Tue, 01 October 2013 19:57 |
rickmike
Messages: 252
Registered: September 2011
Location: United States
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Putting a large tube connecting the front bag to the rear bag would allow more interaction between the bogie arms via the pneumatic coupling. Of course, the small tubing provides some dampening. I don't know where the optimum would be.
I think that I would opt for a large tube to maximize the pneumatic coupling between the bags. This would also minimize the stress on the mounting plate.
Rick M.
1974 26' Canyonlands
aka "The General"
Clinton, TN
[Updated on: Tue, 01 October 2013 20:02] Report message to a moderator |
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| Re: [GMCnet] Rear suspension air bag comparison and the 4 by 4 [message #224308 is a reply to message #224290] |
Wed, 02 October 2013 05:26 |
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Loffen
Messages: 1087
Registered: August 2013
Location: Norway
Karma: 1
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So, after reading the posts is the new A Sirum 4 bag system the gold middle route with the floating paddle ?
I have done some over night thinking about this system and got some questions.
First of all the middle paddle, how much movment will it really see (forwad/backwards) and that makes me think of how it is attached to main control arm bracket, I am sure the bolts are strong enough, but would it not have been nice with some sort of bushing or at least a grease fitting at the joint ?
The sideways movment of the paddle do not worry me to much, the paddle looks pretty strong and it would not be a big deal to reinforce it if that would ever be needed.
There is another problem however, the hight of radius between the front and rear control arm will not be constant and the hight of the paddle is, will the air bags deal with the hight differences ?
And last, if you have an air bag blow out, would the last air bag make enough hight to the wheels so you can limp home ?
1973 23' # 1848 Sky Blue Glacier called Baby Blue and a 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Green,
And sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway
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| Re: [GMCnet] Rear suspension air bag comparison and the 4 by 4 [message #224334 is a reply to message #224308] |
Wed, 02 October 2013 10:01 |
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Good thinking.
The paddle in the middle, though it can go to and fro (back and forth) it
cannot travel side to side. The air bag, when on a curve and encountering
bumps, will tend to twist. That twisting motion is limited by the amount of
travel with the paddle in the middle when compared to a single air bag over
the same amount of space (measured horizontally). At that point, the issue
becomes a question of how much lateral twisting can it withstand?
I'm not sure I totally understand your question with regards to height.
Since the paddle is moveable where it connects to the air bags, any pressure
put on the forward wheel will create the equal and opposite reaction of
moving pressure in a rearward manner until the pressure is equally divided.
In this manner, the vertical movement of the coach at that point is not as
great as that to be experienced with a system in which there is a stabilizer
between the airbags immediately above the bogies. Of course, the flexing of
the tire has some effect since the tire, bogie and arms, and airbag all
dynamically interact with each other.
Byron Songer
Louisville, KY
Espen Heitmann wrote:
> So, after reading the posts is the new A Sirum 4 bag system the gold middle
> route with the floating paddle ?
>
> I have done some over night thinking about this system and got some questions.
>
> First of all the middle paddle, how much movment will it really see
> (forwad/backwards) and that makes me think of how it is attached to main
> control arm bracket, I am sure the bolts are strong enough, but would it not
> have been nice with some sort of bushing or at least a grease fitting at the
> joint ?
>
> The sideways movment of the paddle do not worry me to much, the paddle looks
> pretty strong and it would not be a big deal to reinforce it if that would
> ever be needed.
>
> There is another problem however, the hight of radius between the front and
> rear control arm will not be constant and the hight of the paddle is, will the
> air bags deal with the hight differences ?
>
> And last, if you have an air bag blow out, would the last air bag make enough
> hight to the wheels so you can limp home ?
> --
> 1973 Seqouia in Norway
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Byron Songer
Full-timing to enjoy the USA
Former owner but still an admirer
GMC paint schemes at -
http://www.songerconsulting.net
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| Re: [GMCnet] Rear suspension air bag comparison and the 4 by 4 [message #224336 is a reply to message #224334] |
Wed, 02 October 2013 10:17 |
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Loffen
Messages: 1087
Registered: August 2013
Location: Norway
Karma: 1
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Regarding the height, the connecting point between the air bag and the arm will make a radius when the arm goes from the full down to the full up position.
So with to arm oposit to each other there will be a straight line between the two connecting points that moves up and down with the arm movement.
However with the paddle you will get a more or less fixed hight point in the middle of the line between the arms.
My question is if that fixed point will make any trouble for the air bags.
1973 23' # 1848 Sky Blue Glacier called Baby Blue and a 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Green,
And sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway
[Updated on: Wed, 02 October 2013 10:26] Report message to a moderator |
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| Re: [GMCnet] Rear suspension air bag comparison and the 4 by 4 [message #224342 is a reply to message #224336] |
Wed, 02 October 2013 11:07 |
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Loffen
Messages: 1087
Registered: August 2013
Location: Norway
Karma: 1
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| Loffen wrote on Wed, 02 October 2013 17:17 |
Regarding the height, the connecting point between the air bag and the arm will make a radius when the arm goes from the full down to the full up position.
So with to arm oposit to each other there will be a straight line between the two connecting points that moves up and down with the arm movement.
However with the paddle you will get a more or less fixed hight point in the middle of the line between the arms.
My question is if that fixed point will make any trouble for the air bags.
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Here is an example of what I mean, if the RV's rear tires are standing on a level surface and the front wheels ar going up a ramp, the front rear wheel will go down and move the connecting point to the airbag up.
The rear rear wheel will go up and push the connecting point down, all good so far.
So to the paddle arm, the middle point of travell will be when it is straight up, that is also the highest point any forward or rearward movement will push the connecting point down.
That does mean that in this situation the FR point goes down, the point of the paddle goes even further down and the RR point will go up.
Then the interesting question is if the airbags will handle the hight difference between the RR up point and the paddle down point ?
The original bag would not have any problems due since the angle between the Fr and RR arm points would be pretty moderate due to the lenght between the points.
On the system with the mowing paddle the lenght between FR/RR and the paddle will be about half of the original lenght and the difference in hights between the two points will be greater.
1973 23' # 1848 Sky Blue Glacier called Baby Blue and a 1973 26'-3 # 1460 Parrot green Seqouia Known as the Big Green,
And sold my 1973 26'-2 # 581 White Canyon lands under the name Dobbelt trøbbel
in Norway
[Updated on: Wed, 02 October 2013 11:09] Report message to a moderator |
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