Quad Airbag suggestions?

[RF_Burns]

FYI, Cinnabar bought from GM the rights to manufacture parts and manuals for the GMC Motorhome many years ago so they know the GMC motorhome inside out.
They build parts (or have them built) to OEM specs hence they have the tolerances from the 70's. When I got my GMC, the mechanic had me replace the idler arm and the relay arm. I noticed the steering wasn't great and there was a good amount of slop in those two parts. I then bought replacements.. again from Dave lenzi who builds them to tighter tolerances and there was a world of difference!

 

[MarkR]

My coach came with a quad bag setup, likely very expensive, and I viewed it as a disappointment. For all the reasons Bruce mentioned. Those bogies were designed to oppose each other. Just look at the way they handle speed bumps in succession. It was a great design, and I'm bummed that it was defeated on my coach. I'd have much preferred that the PO spent $800 on stock replacements instead, rather than getting sucked into the hype of the quad bag setup.

Of course, I could limp the coach around short distances on 5 wheels, for whatever that's worth. And really, compared to my last Class A coach, this thing still rides like a dream.

I got sucked into that hype and only looked for coaches that were upgraded to quad bags (among other things on the must-have list). Now I realize most of the hype was not applicable to me. I have a new spare, a jack and AAA+RV and if that can’t keep me from being stranded for a bit, then I guess I’ll just have to relax in my MotorHome until the cavalry arrives.

i asked Cinnabar to restore the OE system since I was having a lot of steering and suspension work done anyway. They ended up declining to do so because the Portwagon is too modified and too heavy. I was quite disappointed.

But DANG! it sure rides nice in spite of those dumb old quad bags!

 

[pvfjr]

I got sucked into that hype and only looked for coaches that were upgraded to quad bags (among other things on the must-have list). Now I realize most of the hype was not applicable to me. I have a new spare, a jack and AAA+RV and if that can’t keep me from being stranded for a bit, then I guess I’ll just have to relax in my MotorHome until the cavalry arrives.

i asked Cinnabar to restore the OE system since I was having a lot of steering and suspension work done anyway. They ended up declining to do so because the Portwagon is too modified and too heavy. I was quite disappointed.

But DANG! it sure rides nice in spite of those dumb old quad bags!

Agreed. The stock system is conceptually better, but I still can't complain about the quad bag setup. I bought us a starter RV two years back. A 27' Thor ColumBus from 1993 with a P30 chassis and a TBI 454. Got 7.5 MPGs, did "OK" over most mountain passes, swayed around every corner, and launched you into stratosphere every time the rear end went over a speed bump. It was a great strategy for adjusting our perspective! It will forever serve as our benchmark for determining how awesome the GMC is.

 

[Scotty]

...

i asked Cinnabar to restore the OE system since I was having a lot of steering and suspension work done anyway. They ended up declining to do so because the Portwagon is too modified and too heavy. I was quite disappointed.

But DANG! it sure rides nice in spite of those dumb old quad bags!

I'm a bit confused -
if Cinnabar is advocating for the OEM designed single air bag system, has the purchased rights to sell and support, and advertises themselves as having a complete motorhome service center with a 25,000 pound lift, and offer renovation services, then why would they decline restore it.

 

[Matt Colie]

Migizi,
You have never (that I saw) fully described your coach. Yes, Royales are heavy, but if any other change was done to the rear suspension, brakes and wheels, they may chose not to touch it for liability reasons.

 

[Scotty]

Migizi,
You have never (that I saw) fully described your coach. Yes, Royales are heavy, but if any other change was done to the rear suspension, brakes and wheels, they may chose not to touch it for liability reasons.

my signature file states ‘1978 GMC Royale - Rear Bath’, what more information do you recommend that I add to the descripion?

gotta say i’m still confused with Cinnabar's refusal to restore your coach to OE, using Liability as an excuse would be a poor copout for the reasons i mentioned above.

…Heavy? still less than 1/2 the weight of their 26,000 pound lift.

 

[Matt Colie]

Migizi,
Yes, you say it is a RoyaleRB, but then you said is has a quadbag reaf and never said which of the four quad-bag systems it has. Not all of them can be reverted easily.
You should also know that Cinnabar has had some failures of the off-shore airsprings that they use. I am told that the part has been redesigned, I do not know how well it does at higher loads.
Matt

 

[Scotty]

Migizi,
Yes, you say it is a RoyaleRB, but then you said is has a quadbag reaf and never said which of the four quad-bag systems it has. Not all of them can be reverted easily.
You should also know that Cinnabar has had some failures of the off-shore airsprings that they use. I am told that the part has been redesigned, I do not know how well it does at higher loads.
Matt

i stated in my first post that it had the original air bags, and i am considering quad bags, that was the premise for this topic.

i was almost convinced to stay with the OE single bags, but have decided to go quad.
Im sure some will frown on that decision, but, but i gotta be me

 

[dsmithy]

I've had quad bags from Applied for several years. Great ride, no issues whatsoever. Maybe some reduction in overall travel for leveling as Matt Colie mentioned in a different thread. But we like them.

 

[Matt Colie]

Migizi,

I guess I missed that way back in the thread. That be the case, I guess I am as surprised as you. I wonder if they didn't understand what you were asking for. '78 had two very different systems and maybe they didn't understand.

Matt

 

[LarryW]

I've had three different systems on my coach in the last 18 yrs. The OEM system when I bought it, I drove for about 7yrs. Worked fine running at about 80lbs. But they were original from 1978 and looking pretty bad. So I bought the Sully system and had it waiting at home for me to install. On the way home from Florida that winter, we stopped at our daughter's home in Minnesota. I leveled up, and 20 minutes later, with a HUGE BANG, the passenger side bag blew out and put me on the ground. I was carrying a spare (almost worse than the one that blew) so I installed it and drove the 70mi home. Installed the Sully system (easy install) and found ride height at 45lbs. I can't say I noticed a nickels worth of difference in ride between the Sully system and OEM. But the lower pressures put less strain on every thing in the punematic system. It aired up quick and had almost the same range of motion. I liked it, and was a lot less money than replacing with the OEM bags. In addition, my decision to run with the Sully. system was influenced by rumors of the failure of the off shore OEM bags coupled with replacement bags of the Sully system could be found at most any truck stop. Finally, the bags used in the Sully system are designed for use on 18 wheelers and on our coaches running at 45 to 60 lbs are WAY over rated for the 8000lbs we are carrying on our coaches. Well then sfter running those for 7yrs, I installed the Lenzi disc brake system on the rear of our coach. Problem then is that the low pressure of the Sully system coupled with the pole vaulting effect of heavy braking allowed the rear axle to lock up way to easy flat spotting tires. So, I bought a used Harrison system that I got cheap (Harrison system is the original 4 bag) and installed that. A comparatively difficult install with typical pressures running around 100psi. Again, I can't feel a nickels worth of difference in the ride, but because of the way the Harrison system works, the locking up of the rear axle no longer happens. I've had to adjust the pressure regulator up to it's max at 150lbs in order to get it to turn on for leveling when I need to jack the rear up for site leveling. I wish I could find a larger replacement bag for the Harrison bag to bring the pressures down. There is one bag that will fit, but only slightly larger. Anyway, that's my story, hope it helps someone making decisions on system swaps.

 

[pvfjr]

Anyway, that's my story, hope it helps someone making decisions on system swaps.

Thanks for taking the time to share your experience, Larry. It's invaluable hearing objective opinions from someone who's had all three on the same coach.

 

[Scotty]

Great Info Larry - thanks!

Anyone know how the original Harrison system differs from the latest offering of the Quadra system from Allied/Coop?

 

[billvv]

I've had three different systems on my coach in the last 18 yrs.

Almost the same here.... OEM and 'BANG'! (sitting in driveway), Sully bags, Lenzi discs (no flat-spotting yet), and now a used Quad Bag system (#50) ready to install.

 

[Matt Colie]

Larry,
Thanks for the definitive write up. I'm going to stay with the stock as long as I can but I also have gone to the "Floating Backplates aka Reaction Arms" so I don't flatspot new tires anymore.
Matt

 

[MarkR]

I bought a used Harrison system that I got cheap (Harrison system is the original 4 bag) and installed that. A comparatively difficult install with typical pressures running around 100psi. Again, I can't feel a nickels worth of difference in the ride, but because of the way the Harrison system works, the locking up of the rear axle no longer happens. I've had to adjust the pressure regulator up to it's max at 150lbs in order to get it to turn on for leveling when I need to jack the rear up for site leveling. I

I hope you just solved a mystery for me. My PO instructed his son to fill the bags to 125 lbs and lock em down at the cutoff valve. He never drove with it in Travel. When I did, the pressure was never much less than that, maybe 100-115 lbs. I wonder now if that’s the system you described as the Harrison system. And you still have it on your coach and it’s normal to drive around at 100+ lbs? Other than the high pressure, how might you identify that system?

 

[LarryW]

I hope you just solved a mystery for me. My PO instructed his son to fill the bags to 125 lbs and lock em down at the cutoff valve. He never drove with it in Travel. When I did, the pressure was never much less than that, maybe 100-115 lbs. I wonder now if that’s the system you described as the Harrison system. And you still have it on your coach and it’s normal to drive around at 100+ lbs? Other than the high pressure, how might you identify that system?

Here is a pic of the Harrison 4bag system. Should help you in identifying your system.

4 bagger - harrison

<p><a href="http://gmc.mybirdfeeder.net/GMCforum/index.php?t=msg&rid=0&th=22753&goto=178244">http://gmc.mybirdfeeder.net/GMCforum/index.php?t=msg&rid=0&th=22753&goto=178244</a></p><br /> <p>Read here</p>

www.gmcmhphotos.com

I leave the auto leveling system set on automatic while driving. Keeps it level as I get lighter using up 30-40 gallons of fuel. Levels out at 100-115lbs depending on the load I'm carrying when we travel south. Sometimes if I have a big "Daddy do list" at my daughters home, I may load up with tools, or stuff for the GMCMI rally. Adds weight and in turn more PSI to the bags. JWID

BTW, I experimented with some "Airbagit" air springs that had aluminum mounting plate. Seemed like the perfect solution. Bigger bag, same mount bolting and air placement. Got me down under 90lbs, but that aluminum under the strain of the minor twist it has to endure when inflating to 140ls on a full "up" was enough to crack the aluminum plates and thus leak most of the air over night. Took exchanging several cracked plates with "Airbagit" before they relented that the design was for a streight push on the plate rather than the slight twist. A learning experience I don't want to endure again. There are two bags out there that appear to work just fine. The original was a Firestone W01-358-7659 at 7.44" diameter. "Torque" makes an identical bag #7659 at half the price. Firestone makes a W21-760-0335 at 7.52" diameter. Slightly bigger in diameter so slightly lower pressures, same mounting and air, at Firestone prices. HTH

​

 

[MarkR]

Here is a pic of the Harrison 4bag system. Should help you in identifying your system.

Sure does look like mine. Thanks so much Larry. I appreciate your sharing your experiences with these various systems as I’ve been wondering which quad bag setup I had on the Portwagon.

Glad to know mine isn’t the outlier I thought it was.

 

[LarryW]

I know some are not in favor of some of the aftermarket airbag systems. The original single bag system back in the 70's was way ahead of its time, and even now, certainly a good option for those who want to keep it original. But consider these points.

For the quad bag system (4bag), the bags are readily available from several manufactures and are 1/4 to 1/2 the price of the OEM replacement bags. The bags used in these systems are brought over from systems designed for use on trucks and might be considered way over rated when used on the GMC. Most are readily available at Amazon and other online sources and can be found at many truck stops and truck repair facilities. These bags are designed for long term over the road use and will probably out live you, so considering longevity and availability no need carry spare. The OEM Bags are only available from a limited number of sources, and because of the low production numbers, are quite expensive.

In addition, the quad and 4bag systems, by design, have a solid mounting plate between the bags. The nature of this setup allows both bags to be inflated equally to...say... 110psi. When under hard braking, while the single bag systems may unload the rear tire (sometimes called "pole vaulting") leading to that tire loosing traction (skidding), the quad/4bag systems have a single bag for each arm and keep a full 110PSI of down force on both bogie arms, with no pole vaulting effect and little or no transfer of weight to the front arm, thus significantly reducing rear wheel loss of traction. This becomes significant when going to the heavy duty disc systems that can be installed on the front axle (of the rear).

It could be said that the solid plate between the two bags does not allow for a smooth ride over bumps like speed bumps. I have noticed no difference in coach handling between the original or Sully systems as compared to the 4bag over speed bumps. Felt the same to me, and I've tested this at speeds exceeding 30mph. A smooth ride back there.

Don't be feeling bad about inheriting a 4bag system. IMO, a good design and worth keeping. As a side note, some have experienced some bending of the stationary center plate under severe use. One simple mod you might consider: (ignore the Airbagit bags)

Harrison reinforcemnet

Harrison 4bagger installed with Airbagit bags

www.gmcmhphotos.com

or

Harrison air bag center brace

<p>1-1/2" diameter, 0.2" wall SS tubing. ~1.75" long. The tube fits in the 1-1/2" holes in the bracket and contacts the support plates on the airbags.</p><br /> <p>It would have been a lot easier to use aluminum tube.</p>

www.gmcmhphotos.com

Nothing to worry about here, only a very few reported incidences.

So, just my relatively informed gut level, back yard mechainc eyeball it up and guestimate observations, that's all.

 

[PeteSr]

I am not a fan of the quad bag system for one simple reason. It does away with the air spring compliance that gives the GMC it's superior ride characteristic by having the bag react against the fixed plate. And it's supposed advantage is that it gives redundency by allowing you to run on one tire. But, the GMC single rear suspension arm and tire are not designed to take the entire load of the coach (side). In other words it overloads the rear suspension components. So, I don't see any advantage to it.