Home » Public Forums » GMCnet » Tried Coil Springs with inside airbags ?
| Tried Coil Springs with inside airbags ? [message #190010] |
Mon, 12 November 2012 15:02  |
Francois
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Location: Southern California
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I keep looking at the rear suspension, and although I am happy with the way it rides, There is a slow leak on one side and I keep wondering what might happen in a bag blowout and what might be better.
Among the modifications I have seen are 4x4 posts in there, and I have seen the photo of the guy who put in Ford F350 coil springs. I note also that there are easily available air bags that fit inside coil springs- for almost any vehicle. Maybe it's me, but a system like that would eliminate one worry on my 78 Royale, and I like eliminating worries, especially when the total cost would be so much less than even replacing the bags I have.
The airbags inside of the coils would seem to be able to adjust height and ride, similar to the current system, but if the bag or the compressor or the lines failed, not a major sweat.
Is this thinking wrong? Has anyone in the community tried this?
Thanks.
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| Re: Tried Coil Springs with inside airbags ? [message #190014 is a reply to message #190010] |
Mon, 12 November 2012 15:25  |
Carl S.
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Location: Tucson, AZ.
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| Francois wrote on Mon, 12 November 2012 14:02 |
I keep looking at the rear suspension, and although I am happy with the way it rides, There is a slow leak on one side and I keep wondering what might happen in a bag blowout and what might be better.
Among the modifications I have seen are 4x4 posts in there, and I have seen the photo of the guy who put in Ford F350 coil springs. I note also that there are easily available air bags that fit inside coil springs- for almost any vehicle. Maybe it's me, but a system like that would eliminate one worry on my 78 Royale, and I like eliminating worries, especially when the total cost would be so much less than even replacing the bags I have.
The airbags inside of the coils would seem to be able to adjust height and ride, similar to the current system, but if the bag or the compressor or the lines failed, not a major sweat.
Is this thinking wrong? Has anyone in the community tried this?
Thanks.
|
You may be on to something. The main drawback would be determining the ideal spring rate. It would need to allow the rear of the coach to drop down as low as the original air spring does in order to maintain the full adjustability of the rear suspension for campsite leveling purposes. I believe that would still allow the rear end to drag if one of the internal air bags blew out, defeating the purpose somewhat..
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: Tried Coil Springs with inside airbags ? [message #190021 is a reply to message #190019] |
Mon, 12 November 2012 15:56 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
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| Francois wrote on Mon, 12 November 2012 14:51 |
I think having all the adjustability of the current system would be asking too much. I am thinking that the system would not go as low as the current one. I think that would be necessary for a system that would let you know when a bag blew out, but for which there would be no issue about continuing to drive at a reasonable speed.
I agree that finding the right spring length and load would be an issue. I am also thinking that a variable rate coil spring, as opposed to a constant rate coil spring would be preferred.
Thanks for responding
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If you're willing to compromise on down travel, I don't see why your idea wouldn't work. With a little research and experimentation, you might be able put a workable system together.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] Tried Coil Springs with inside airbags ? [message #190022 is a reply to message #190014] |
Mon, 12 November 2012 16:28 |
storm'n
Messages: 492
Registered: April 2007
Location: Ont. Can
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The GM P-30 MH chassis had a Ride Rite air bag inside the front coil springs. If these bags lost their air the suspension rode on the stop blocks. I think the recommended pressure was 60 psi.
Norm.
Francois wrote on Mon, 12 November 2012 14:02
> I keep looking at the rear suspension, and although I am happy with the way it rides, There is a slow leak on one side and I keep wondering what might happen in a bag blowout and what might be better.
>
> Among the modifications I have seen are 4x4 posts in there, and I have seen the photo of the guy who put in Ford F350 coil springs. I note also that there are easily available air bags that fit inside coil springs- for almost any vehicle. Maybe it's me, but a system like that would eliminate one worry on my 78 Royale, and I like eliminating worries, especially when the total cost would be so much less than even replacing the bags I have.
>
> The airbags inside of the coils would seem to be able to adjust height and ride, similar to the current system, but if the bag or the compressor or the lines failed, not a major sweat.
>
> Is this thinking wrong? Has anyone in the community tried this?
>
> Thanks.
You may be on to something. The main drawback would be determining the ideal spring rate. It would need to allow the rear of the coach to drop down as low as the original air spring does in order to maintain the full adjustability of the rear suspension for campsite leveling purposes. I believe that would still allow the rear end to drag if one of the internal air bags blew out, defeating the purpose somewhat..
--
Carl S.
'75 ex Palm Beach
Tucson, AZ.
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| Re: [GMCnet] Tried Coil Springs with inside airbags ? [message #190040 is a reply to message #190032] |
Mon, 12 November 2012 17:54 |
Francois
Messages: 161
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Location: Southern California
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I think, although I may be wrong, that an air spring inherently is a variable rate spring, and that the cone system was intended to calibrate the variability rate rather than to create it.
I may be wrong though.
| Robert Mueller wrote on Mon, 12 November 2012 14:56 |
I think you are correct, I read somewhere that the cones inside the OEM air bags are tapered, the GMC engineers that designed the
system did that to create a variable spring rate.
Regards,
Rob M.
USAussie - Downunder
-----Original Message-----
From: Sigmund Frankenfelter
I think having all the adjustability of the current system would be asking too much. I am thinking that the system would not go as
low as the current one. I think that would be necessary for a system that would let you know when a bag blew out, but for which
there would be no issue about continuing to drive at a reasonable speed.
I agree that finding the right spring length and load would be an issue. I am also thinking that a variable rate coil spring, as
opposed to a constant rate coil spring would be preferred.
Thanks for responding
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| Re: Tried Coil Springs with inside airbags ? [message #190065 is a reply to message #190010] |
Mon, 12 November 2012 18:57 |
bwevers
Messages: 598
Registered: October 2010
Location: San Jose
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Francois,
I think the problem with fitting the airbag inside the coil
spring is that it doesn't give you a lot of travel.
The spring ID is 4 inches, which gives around 12.5 square inches.
With 100 PSI you can get 1250 LBS force. And the E350
springs are 400 - 600 LBS/inch. So you would be able
to change ride height 2 to 3 inches at the spring, This is
less travel than what the stock airbags will give you.
Regards,
Bill
Bill Wevers GMC49ers, GMC Western States
1975 Glenbrook - Manny Powerdrive, OneTon
455 F Block, G heads
San Jose
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| Re: Tried Coil Springs with inside airbags ? [message #190101 is a reply to message #190065] |
Tue, 13 November 2012 01:59 |
Francois
Messages: 161
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Location: Southern California
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| bwevers wrote on Mon, 12 November 2012 16:57 |
Francois,
I think the problem with fitting the airbag inside the coil
spring is that it doesn't give you a lot of travel.
The spring ID is 4 inches, which gives around 12.5 square inches.
With 100 PSI you can get 1250 LBS force. And the E350
springs are 400 - 600 LBS/inch. So you would be able
to change ride height 2 to 3 inches at the spring, This is
less travel than what the stock airbags will give you.
Regards,
Bill
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Although I don't understand how you can compute how much the travel would be based upon those figures, I do think the system would be a compromise. It might end up not going as low as the current system, but with the right coil spring, it should be able to go as high. All of the systems out there involve some kind of compromise though.
When I consider that most campsites approximate level, big height adjustments don't seem so critical.
It looks like an inexpensive enough experiment. I have an inquiry in on a pair of Moog variable rate springs for a Ford.
The whole thing should cost around 250 bucks, airbags included. With it, I get the kind of suspension action designed in by the GM engineers, and I don't have to worry about blowouts, a tweaked chassis or other damage.
I am not going to do it if I can't use off the shelf components - no custom machining for example. It has to be an available coil spring and an available inner airbag.
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| Re: Tried Coil Springs with inside airbags ? [message #190132 is a reply to message #190101] |
Tue, 13 November 2012 09:59 |
habbyguy
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Francois, I've often wondered the same thing (whether a "stock" coil / air bag from another vehicle would work in place of a GMC air bag). I've seen a couple systems on "truck-oriented TV shows" that put pretty enormous air bags inside pretty enormous spings for pretty enormous trucks. I think adapting any of the systems to a GMC would involve at least some fabrication but might end up being a very viable alternative to an air bag, and maybe more importantly, with a failure mode that doesn't leave you imobile. But good luck with your search, and of course - keep us all posted as to how it all works out.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] Tried Coil Springs with inside airbags ? [message #190165 is a reply to message #190143] |
Tue, 13 November 2012 14:14 |
Russell Mehlenbacher
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Registered: June 2010
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We spent a night in a Michigan State Park, (late arrival, 3 sites to choose
from) with the DS rear bumper touching the ground and the PS front tire
jacked OFF the ground. Early AM strolling campers got a laugh out of it.
Russ
On Tue, Nov 13, 2012 at 12:09 PM, Matt Colie <matt7323tze@gmail.com> wrote:
>
>
> Francois wrote on Tue, 13 November 2012 02:59
> > <snip>
> > When I consider that most campsites approximate level, big height
> adjustments don't seem so critical. <snip>
>
> Francois,
> If you are talking paid-a-lot-for campsites on treeless plains, I might
> agree, but we have hold up for the night in parking lots and rest areas
> that are a challenge to get the coach level enough so things didn't slide
> off the table. I have often ended up with no air all on one or the other
> side of the rear.
>
> Matt
> --
> Matt & Mary Colie
> '73 Glacier 23 Chaumière (say show-me-air) Just about as stock as you will
> find
> SE Michigan - Twixt A2 and Detroit
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--
Russ & Linda Mehlenbacher
Rochester Hills, MI
'74 X-Sequoia
'76 Eleganza
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'74 Sequoia
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| Re: Tried Coil Springs with inside airbags ? [message #190295 is a reply to message #190010] |
Wed, 14 November 2012 14:37 |
Francois
Messages: 161
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Location: Southern California
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Just an update, I measured the length of my airbags plus cones - as far up as I could get them, then as far down.
I got an "up" length of 17 inches and a "down" length of 12 - 13 inches. I have a concept for 1/4 inch steel plates on the ends of the coil springs,(basically a square piece with the corners bent up to contain the spring) so that would add 1/2 inch to the total spring length.
The Ford (heavy duty) variable rate springs I was looking at are 15 3/4 inches. With the 1/4 inch plates sitting on the bogey eye, that's only 16 1/4 inches. If I were to use them, I would have to shim them out another inch, since I don't want the inner airbag to be working against the coil spring, but with it.
Also, I have no idea on the load on the system as it now sits, so I am kind of flying blind where this measurement is concerned. Anyway, I carry on.
If anyone has an idea about the load on our airbags, that would be helpful in my search.
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| Re: [GMCnet] Tried Coil Springs with inside airbags ? [message #190298 is a reply to message #190295] |
Wed, 14 November 2012 15:04 |
James Hupy
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Weigh the coach, first the front axle, then the intermediate, and finally
the rear. Should give you the info you need. If you can not find a scale,
come to a western states rally and we will weigh it there for you.
Jim Hupy
Salem
78 Gmc Royale 403
On Nov 14, 2012 12:37 PM, "Sigmund Frankenfelter" <ziggy.frankenf@gmail.com>
wrote:
>
>
> Just an update, I measured the length of my airbags plus cones - as far up
> as I could get them, then as far down.
>
> I got an "up" length of 17 inches and a "down" length of 12 - 13 inches. I
> have a concept for 1/4 inch steel plates on the ends of the coil
> springs,(basically a square piece with the corners bent up to contain the
> spring) so that would add 1/2 inch to the total spring length.
>
> The Ford (heavy duty) variable rate springs I was looking at are 15 3/4
> inches. With the 1/4 inch plates sitting on the bogey eye, that's only 16
> 1/4 inches. If I were to use them, I would have to shim them out another
> inch, since I don't want the inner airbag to be working against the coil
> spring, but with it.
>
> Also, I have no idea on the load on the system as it now sits, so I am
> kind of flying blind where this measurement is concerned. Anyway, I carry
> on.
>
> If anyone has an idea about the load on our airbags, that would be helpful
> in my search.
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| Re: [GMCnet] Tried Coil Springs with inside airbags ? [message #190305 is a reply to message #190298] |
Wed, 14 November 2012 15:56 |
Francois
Messages: 161
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Location: Southern California
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Weighing the axles would would provide a starting number of pounds, but that number couldn't be used as the load value of the spring.
The reason I say that is that the bogey arms are levers and there is mechanical advantage involved. (edit note: this may be incorrect. I looked at a photo of the quadrabag system sans wheels and it looks like there is no leverage mechanical advantage involved.)
Just looking at it indicates to me that less pressure is required to move the airbags out than if the bag was lifting the whole side up directly.
I have already read how these coaches are rear-heavy, so with a 12,000 pound gross weight, that would be something over 6,000 pounds on the rear.
If I have to approximate looking at a side view of the coach, I would estimate the rear to be carrying 7,500 to 8,000 pounds. Is this close? I have no idea.
If I can find a number on that (weight on rear axle), I think I would be able to measure lengths and angles and come close to the right load coil spring.
[Updated on: Wed, 14 November 2012 16:21] Report message to a moderator |
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| Re: [GMCnet] Tried Coil Springs with inside airbags ? [message #190316 is a reply to message #190298] |
Wed, 14 November 2012 16:47 |
 |
USAussie
Messages: 15912
Registered: July 2007
Location: Sydney, Australia
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G'day,
I had Double Trouble weighed at a CAT truck scale. CAT scales have a number of pads so they can weigh different sections of a big
rig.
The front pads have a big inverted "U" that the truck fits under. It has a box attached to it with a speaker and a mike to
communicate with the scale operator in the building.
I spoke to the young lady that ran the scales before I pulled on the scales and explained that I wanted to take three weights of
Double Trouble:
1) Full weight - I would pull the front wheels on the second pad and the rear wheels on the third pad
2) Drivers side weight - I would pull the driver side front wheels on the second pad and the driver side rear wheels on the third
pad - the passenger side wheels would be off the scales
3) Passenger side weight - I would pull the passenger side front wheels on the second pad and the passenger side rear wheels on the
third pad - the driver side wheels would be off the scales
The front wheels have to be on the second pad because the inverted "U" precludes getting wheels off the scale.
She charged me $12.00 for the first weight and $1.00 each for the second and third weight making a total of $14.00. I reckon those
weights are as accurate as you're going to get anywhere.
Regards,
Rob M.
USAussie - Downunder
AUS '75 Avion - The Blue Streak TZE365V100428
USA '75 Avion - Double Trouble TZE365V100426
-----Original Message-----
From: James Hupy
Weigh the coach, first the front axle, then the intermediate, and finally
the rear. Should give you the info you need. If you can not find a scale,
come to a western states rally and we will weigh it there for you.
Jim
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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] Tried Coil Springs with inside airbags ? [message #190357 is a reply to message #190305] |
Wed, 14 November 2012 22:00 |
Carl S.
Messages: 4186
Registered: January 2009
Location: Tucson, AZ.
Karma: 13
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Francois,
I had my 26' coach weighed a few years ago at the GMCMI in Pueblo. IIRC, at that time, each wheel was within about 150 lbs of 2,000#. That would put the rear of the coach at around 8,000#.
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, Solar battery charging. GMCSJ and GMCMI member
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| Re: [GMCnet] Tried Coil Springs with inside airbags ? [message #190392 is a reply to message #190357] |
Thu, 15 November 2012 11:57 |
Francois
Messages: 161
Registered: October 2012
Location: Southern California
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| Carl S. wrote on Wed, 14 November 2012 20:00 |
Francois,
I had my 26' coach weighed a few years ago at the GMCMI in Pueblo. IIRC, at that time, each wheel was within about 150 lbs of 2,000#. That would put the rear of the coach at around 8,000#.
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Thanks much. That was in the high range of what I was estimating, but I am going to use it.
I took a look at air shocks as a possible alternative to airbags inside the coils. Unfortunately, I can't get my questions answered on them. I asked for a size chart and whether you could mount them horizontally. All I got was "we don't make air shocks for motorhomes".
I am back to the inner airbags.
I am going to order the coil springs today, I am going to mount them without the inner bags and then lower the coach and see where it sits. They have coil spring spacers in various thicknesses. They are aluminum and mount on the end of the coil. Once I see where the coach sits, I will have an idea if and how much spacing is needed.
I am also flirting with a pivot concept, where the spring stays straight throughout its travel. So far I haven't come up with an approach that doesn't require machining and welding. I am sticking with my off-the-shelf approach, but if I see a way to do the pivot thing without going custom, I might still do it.
[Updated on: Thu, 15 November 2012 12:07] Report message to a moderator |
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