Replacements for the original single air bag system was discontinued by Firestone several years ago. Immediately folks started rigging up replacement solutions using huge spacers and bag not suited for the job. Their intentions were good but engineering a improved air ride suspension for the GMC takes more than good intentions. Our “quad bag” rear suspension upgrade was a collaboration of many years of in the field research and development. Computer failure tested this system is safer, more serviceable and has superior performance to any system used before including the original.
Features:
- 2 piece construction for easy installation
- Outboard air line connections to air bags for easier connections
- Heavier gauge steel construction (3/8″)
- Double 3/8″ steel plates back to back between the air bags, no flex here!
- Larger, more weight carrying air bags
- Lower air pressure requirements (keeps operating pressures well under manufacturer recommendations.
- More travel up and down for height adjustment mainly because of the design.
Cost: $1798.95 plus shipping (yes, it is higher priced than another system out there but proper design parameters require this) Remember, with this or any other quality designed and built part, you will always get what you pay for, do not buy this component from the “lowest bidder”. Oh, and if you see a 4 air bag system for less– that is just what it is!
Installation will take between 5-7 hours for both sides
Why consider a 4 air bag system? Besides not having the original 2 sided air bag available, this “Q bag” system really is the “better mousetrap”
Three main reasons,
1. Safety 
if you blow a rear tire or one of the original style air bags of your rear suspension, you are stopped where you are. There is no moving until you replace that tire or bag. Tell me at 2AM, on the side of the highway with trucks blowing past you while you stand in the rain in an ant bed if this is an inconvenience. With the new 4 air bag system, you can actually continue to drive carefully on 3 or even 2 rear tires and blow out 1 air bag on each side of the coach and still move to a safe place to effect permanent repairs. Of course your system will be overloaded so please be careful and only do this as an emergency situation dictates. In effect, there is no need to carry a spare tire, if a front tire blows out, simply shift a rear tire up front and drive on to a local tire store. Safety is the number 1 reason to have the quadrabag system.
2. Retrofit to new parts 
As our coaches get older, so do its parts and the eventual shortage of the few specialty replacement parts that keep them on the road. The original air bags are an exclusive component only available at a handful of specialty dealers and rather expensive. This new 4 air bag system uses air bags that can be found on the shelf at most any RV dealership or supply store. No need to pack away an extra air bag in your coach, no need to worry if you will find a new air bag when you need one, this new system does away with that worry. Adapting to newer, higher quality production parts is always a good thing.
3. Performance Not to say the ride of a GMC is not nice, as a matter of fact that is one of the great things of the coach but it would be nicer to have a bit more control, more suspension responsiveness without sacrificing the awesome ride we bought the coach for in the first place. The new 4 air bag system does just that. The difference in handling of a full sized stretch van and a mini van, your GMC will transform from a float like “marshmallow” feel to the responsive, sure footed and have the controlled handling characteristics many want today. Not hard or bumpy or like riding a rail as some have said they experience with the old system, the new design (quadrabag) 4 air bag system gives you more control, better tracking and a sure feel without the rough ride.
And if all that isn’t enough, it really looks cool too! Update and upgrade your classic GMC to a better suspension system, install the all new “quadrabag” 4 air bag system, you will thank yourself.
Now for a few commonly asked questions courtesy of our good friend Rick Williams from up in the cold north country– Michigan
- Are there any changes to the leveling controls (in the wheel well)? No Rick, the new 4 air bag system uses the original leveling system
- Does it work will all leveling systems ( I have an electro level II)? Yes, the new system will run on Power Level, Electro and Electro Level II systems, the new system actually will use less pressure than the original system.
- Does it require compressor upgrades? If your compressor is in good shape, it will supply the new system fine (the new quadrabag system actually requires less pressure from the compressor than the original air bag), but of course original compressors are getting up there in age– it would be a drag to have all of this new stuff air have no air cause that old compressor gave up the ghost! It’s always a good thing to have reliable components and the weakest part will be the one that leaves you.
- What is included in the kit? The kit includes, the 2 piece stationary structure (one for each side), 4 air bags and hardware, 4 arm risers and an air control manifold for each side.
- Do we leave the manual shutoff valves that many of us have installed? Why or why not? The “air control manifold” replaces the air shut off kit from the original bag system and gives you shut offs for each bag for each side and a filler Schrader valve for each side. This manifold will give you total control of the new system.
- Does the “T” skirt still fit? Yes Dave, you will need to modify the lower bracket a bit but it will work.
- Are the air line connections on the outside of the bag dangerous? Let me ask you this– if the original design has it’s connection “on the outside”– is it dangerous? The Quadrabag” system has fittings just llike the original system.
- Does this air bag system make the coach ride rough? More bag pressure relates to the “stiffness” of the ride. The original air bag will bring the coach to “ride height” somewhere around 100 PSI. The early 4 bag system will take more pressure than that, the Quadrabag system will take less than 100 PSI. So, what would be the answer to the question?