Something that I don't remember reading in the literature that came with my kit is that it's best to air them up to the appropriate level before adding the extra load. I find that doing this helps them work better than trying to air up after adding the load.
I think the Airlift instructions actually do say to fill the bags before adding a load... I only noticed that when reading/installing the Airlifts, not the Firestones I had before.
I've had three sets of air-spring overloads, the first two were Firestones. The first set developed a leak in one of the fittings in the top of a bag. They were replaced under warranty. The second set failed with a split in the middle of the bag where the two halves were joined.
After months of no air-springs I purchased a set of Airlift bags. While installing them I noted that the kit seemed better. The air line is softer and there are barbs/nipples on the top of the bags. The rubbery air line is not only pressed onto the barbed fitting, but also has a little hose clamp that helps secure the line. This seems better than the press-in only air line for the Firestones.
I've had the Airlifts for a few months and so far so good. The Airlifts seem to be air tight, I can't put my finger on any leaks thus far.
