I do feel the right leaf spring for the load is better than adding a set of helpers to weak leafs.
In my situation I knew the loads were going to be quite variable, and I went the airspring route, and no regrets.
First thing I noted when driving was when going around turns it did not lean near as much.
Second thing was that 18 wheelers passing me on the highway at 65mph would not really push me all over the road as badly.
On a perfectly level surface I realized I needed about 10 more PSI drivers side than passenger to level it out side to side.
Mine are obviously plumbed separately. I think plumbing the airbags together to share one schrader valve is absolutely and overwhelmingly asinine.
I can see no reason to do so, other than laziness. As if filling them is a hair pulling nightmare scenario or something, and only having to fill one is markedly easier. Bah.
Right now I have most of my tools/weight removed from the van and 5 and 15LB psi evens it out, and 100PSI in both bags pushed the back end up well over 4 inches, and it turns flat, but the headlamps point straight down, it stresses the Driveshaft U joints more, and there is no need. Loaded down the most I use is 35psi drivers side, 25 passenger. A sudden deflation is not likely to cause an accident, though I imagine it depends where/when it were to occur. The bags themselves are so robustly built I doubt catastrophic failure is common. Perhaps the airlines if they get nicked or chafe through.
When urban dwelling 100 psi curbside and 0 PSI drivers side really levels out the bed nicely. I have driven this way and left turns at speed can be scary
Mine have been installed since 2007. The original set of airbags had very slow leaks out of the box, but Summit Autoparts replaced them painlessly, and the replacements lose less PSI than they say is acceptable.
I did use aftermarket PTC connectors and airhose. These are strange connections. One inserts the wire, and that's it, according to the directions. in my experience make sure the cut is absolutely 90 degrees, push it in until it bottoms out, then pull on the hose and sliding collett to ensure a good seal. The 100PSI should force this to occur, but I help it along by pulling on collet and airhose.
I put the Schrader(fill) valves inside my Van to adjust from within. Some put on a controller so they can change pressure from drivers seat. I certainly would have been able to make use of this feature.
Mine were ~235$ in 2007 but I see the same kit is now 100$ more than that.
I am not sure the price of new leaf springs.
If one's load is not variable and campsite leveling is not a concern, then proper metal springs for the load will no doubt ride better than airbag helper springs. They are kind of bouncy and need a more aggressive shock to tame them. I waited 5 months after airbag installation to put on the very firm KYB Gas a Just shocks replacing some bottom dollar Gabriels, and control improved dramatically.
I really like the KYBs, but they certainly are firmer than say Monroe sensa tracs, which felt wallowy and soft to me.
There are other options for helper springs. before I got the Firestone RR's, i used the 35$ helper springs from pep boys that clamp to only the back side of the leafspring and increase the rating. The plastic slider on one end would eventually wera out and metal on metal contact would occur and I'd remove them, and get another set. They certainly helped, but are a halfass solution. Helwig sells a burlier version with no parts to wear out.
If a Van dweller van rear end is sagging badly, not only is it going to handle poorly, but it can also draw unwanted attention. If one does not re aim the headlamps, then nighttime vision suffers, for the driver and drivers on the other side of the road being blinded by headlamps pointed too high.
Really a heavily loaded older van needs something to keep the rear end from sitting too low, if only for handling purposes. I love the adjustability factor of my Airbags, but I am sure this is a detraction to others who want nothing to do with worrying about airbag PSI. When i went up into the Sierras last fall, I'd parked level and went around with a tape measure adjusting PSI until all four corners sat as level as possible, and i was very pleased with the handling on the twisty turny roads. When descending, I pushed the handling limits to the very edge and beyond to see where the edge lay. I am sure a passenger would have been screaming for their life, but I had full confidence in the handling.
One thing to note is that the Exhaust pipe runs fairly close to where the Airbags will reside. I had to cut my exhaust and extend it about an inch for clearance. I also extended the provided heatshield so that no part of the airbag was in direct line of sight withing 6 inches of the exhaust pipe.
My FS RR kit claimed a NO drill installation. BS. It comes with self drilling bolts, and If I did not have proper drill attachments to attach sockets or drilled pilot holes first, installation would be a nightmare.
I am not saying everybody should run out and get airbags to assist the rear leafs, just providing all the information I can think of to add if one does decide to go this route, or help to make a decision whether to go this route or other routes.
I know some have successfully used aftermarket shocks that employ coil springs over the shocks, or perhaps airshocks to assist load carrying ability. I dislike this approach as a Shock can only exert so much force on its mounting hardware, but when these attachment points are also helping to carry the weight of the vehicle, then this force on these points increases greatly, perhaps beyond their design limits.
Also note that if lifting the vehicle by the frame, the airbags are not designed to suspend the entire weight of the axle, and can be damaged by doing so.
