| Air spring vs Hydro-pneumatic suspension [message #187625] |
Thu, 18 October 2012 21:43  |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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There has been considerable discussion here about Citroen and hydropneumatic suspensions, here is how the GMC MH fits in here.
During the early development of the GMC Motorhome, the plan was to use leading/trailing suspension arms supported by a hydro-pneumatic cylinder. Al Carlson was a Buick Engineer that thought the Citroen system was an impressive design and could be adapted to the GMC MH. Ralph Merkle, the GMC MH chassis engineer, was the inventor of the leading/trailing arm suspension and he and Al Carlson put together a design that was used on the pie wagon, the initial demonstration vehicle of the GMC motorhome. The link below shows the chassis of this vehicle, there are other pictures of the completed vehicle in my History CD.
http://www.gmcmhphotos.com/photos/miscellaneous-bryant-stuff/p33070-early-gmc-hydropneumatic-rear-suspension.html
While this design worked very well, it was expensive to build and a cost reduced design was required.
An air spring (bag) was designed and with minor changes approved for manufacture. The rest is as they say, history.
The link below shows an early air bag.
http://www.gmcmhphotos.com/photos/miscellaneous-bryant-stuff/p33069-early-gmc-1st-design-a.html
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
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| Re: [GMCnet] Air spring vs Hydro-pneumatic suspension [message #187658 is a reply to message #187629] |
Fri, 19 October 2012 10:49  |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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Larry,
The key engineer with ideas was Ralph Merkle, responsible for the GMC MH chassis. He started with the idea of the leading/trailing arm suspension and was looking for a GM vehicle that could use that idea. He had the pie wagon built to demonstrate that design (see slides 37, 38 & 39 History CD) and while the pie wagon suspension arms were fabricated the production arms of nodular iron from Central Foundry I don't believe were changed except for the 1 1/4" to 1 1/2" pins.
Its important to understand where Ralph's design was comming from, he wanted a smaller vehicle, using many off the shelf GM components. When others decided they needed a larger (heavier) vehicle for space to fit in all the "extras" Ralph was quite upset. He felt his original design was violated which has pretty much been demonstrated by traction, wheel/tire, rear brakes/spindle/bearing/pin concerns.
With the prototype testing (defined as a modified truck test) I am surprised that more of the early problems were not found, i.e., the rear pin bushings & others. With the increasing GVW from 10,500 to 12,500 and some of us exceeding that, 35+ years and many thousands of miles I think Ralph's idea has pretty well stood the test of time.
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
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| Re: [GMCnet] Air spring vs Hydro-pneumatic suspension [message #187687 is a reply to message #187658] |
Fri, 19 October 2012 16:52 |
LYNN L
Messages: 140
Registered: March 2005
Location: Pearland TX.
Karma: 0
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Bill, I am curious to know if they ever considered an air bagged front suspension. Seems to make sense with a compressor on board and infinite height ajustments.. Been considering doing mine.
Lynn L
76 Eleganza Cad.500
Pearland TX.
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| Re: [GMCnet] Air spring vs Hydro-pneumatic suspension [message #187701 is a reply to message #187687] |
Fri, 19 October 2012 18:55 |
bryant374
Messages: 563
Registered: May 2004
Location: Pleasant Valley, NY 12569
Karma: 1
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Senior Member |
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Lynn,
I never heard any discussions about air bags for the front. I suspect the torsion bar front suspension being a proven design, cheap and simple as compared to air bags was considered sufficient. The new MH as a new design with much complexity I don't believe they were looking for additional complexity and cost.
What necessary function would front air bags provide that the torsion bars don't?
Bill
[GMCnet] Air spring vs Hydro-pneumatic suspension
Fri, 19 October 2012 17:52
LYNN L
Bill, I am curious to know if they ever considered an air bagged front suspension. Seems to make sense with a compressor on board and infinite height ajustments.. Been considering doing mine.
Bill Bryant
PO 1976~PB (owned 34 years)
1914 Ford (owned 70 years)
1965 Corvette (owned 39 years)
GMC Motorhome History
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| Re: [GMCnet] Air spring vs Hydro-pneumatic suspension [message #187742 is a reply to message #187687] |
Sat, 20 October 2012 07:21 |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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| LYNN L wrote on Fri, 19 October 2012 17:52 |
Bill, I am curious to know if they ever considered an air bagged front suspension. Seems to make sense with a compressor on board and infinite height ajustments.. Been considering doing mine.
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Lynn,
In a short discussion with a GMC engineer at the time, they saw the rear suspension as first a way to compensate for weight change and shift at the rear. As the coaches were built as travelers and not really campers (early on), the hope was to maintain the ride and handling with that variation from fuel use and occupant movements. That variation was just not a factor in the front. The fact that it provided a ride unlike any bus/truck based coach was just a wonderful addition. They knew it could be used to level the parked coach and that is was why the controls were not included in the Transmodes headed for shuttle service.
The thing he was disappointed by was the fact that they couldn't lift a rear tire with the shock charge. It was hoped that the vehicle would (like a Citroen) be able to use the rear suspension instead of a jack.
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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