Air suspensions are a popular aftermarket upgrade for trucks and vans that carry heavy loads. Whether it is a work vehicle or a camper, it can help smooth out the ride as well as prevent sagging in the rear end. But how do they affect the structural integrity of these larger, high-roof, unibody chassis vans like the Mercedes-Benz Sprinter? Well, here is our experience that we would like to share with you.
We have owned several vans and trucks in the past. Including our current Sprinter van, we are on our 4th vehicle. The first of which is a 2007 GMC Savana van. It is based on a 3/4 ton truck body-on-frame chassis just like the Chevy Silverado. The next 2 vehicles were Ford Super Duty F-250 full-sized pickup trucks. Again these were stout, body-on-frame chassis built for heavy duty use. We installed airbags on all three of these vehicles and carried heavy loads in them. 2 of them towed our 8,000 lbs Airstream trailer and one of the F-250s carried a truck camper in the bed. They all performed flawlessly over hundreds of thousands of miles.
When we made the switch to a Mercedes Sprinter van, it was natural for us to look at air suspension upgrades again while building out a camper interior. It was going to be a pretty simple build that won’t exceed the load capacity of the vehicle but heavy enough to visibly sag the rear end. We just wanted to bring the stance back up to factory so we installed Super Spring’s Sumo Spring system in the rear.
The installation was very easy and just like the other air springs we’ve used, they utilized the existing factory bump stop brackets. However, after a couple of years of traveling in the van, we were surprised to see that the airbags had caused stress cracks in the unibody frame rails. We feel we were lucky to have caught the issue early enough and were able to make a proper repair to the rails. Rather than continuing to rely on airbags for load support, we opted to add a third leaf to our steel leaf spring pack to help carry the load.
What we believe is the problem is the unibody chassis is just not designed to support the constant extra weight at the bump stop bracket. We could see into the stress crack and there are no visible reinforcements inside the metal frame rails like there is where the leaf spring pack is attached. They are simply there to take the occasional stress on a bumpy road when the spring pack compresses farther than usual.
Having cracked frame rails is a devastating issue on a body-on-frame vehicle like our Ford Super Duty trucks. But on a unibody van like the Sprinter, the entire structure of the vehicle even above the frame rails acts as support for the vehicle and its load. Of course, damage like this is less than ideal and shall be avoided at all costs. We were able to not only repair the cracks in the unibody chassis but also added additional steel plates to further support the area. It is now stronger than it was before and with the third leaf spring installed to carry the camper weight, we are better off now than ever before.
I hope this helps some of you in deciding whether or not to use airbags in your unibody vehicle’s suspension if you plan on carrying at or near the load capacity on a constant basis. Of course there are various styles of air suspension and some will indeed help increase your carrying capacity and use multiple points of support on the chassis. But before deciding on which one to install, keep in mind what your aftermarket parts are built for before going forward.
Here is our story about how we discover the problems and what it took for us to remedy them.
I hope you find this article helpful in your journey to build your own adventure mobile. The bottom line is air suspension on unibody vans in general should only be used for occasional load bearing purposes. If constant load bearing is required, learn from our experience and install additional leaf springs to support the extra weight.