One of our goals for the Hot Rod Hauler was to get it a little closer to the ground and still maintain its load carrying capacity. We weren’t looking for an “in the grass” stance, but two or three inches would do it; we just had to find a way to deal with the twin I-beams up front.
In 1965, Ford introduced the twin I-beam front suspension in trucks. The advertising of the day that announced the revolutionary front suspension proclaimed these vehicles rode like a car and worked like a truck. Twin I-beam suspension offered improved wheel alignment and reduced tire wear the ads went on to say. Some of the illustrations that went along with a few of the early ads showed how when a wheel encountered a bump the other was unaffected. Interestingly, these drawings seemed to indicate that a wheel going over a bump moved straight up and down, however that must have been some ad agency’s version of the engineering involved because in the real world they behaved differently.
Twin I-beam front suspension...
Twin I-beam front suspension made its debut in 1966 and remained fundamentally the same during production. They were simple, tough, and rode reasonably well.
Ford’s twin I-beams were roughly 36 inches long and were attached to the frame on one side of the truck with a coil spring, shock, and the wheel at the other—forged steel radius arms located the axles front to rear. And while it was true that one front wheel could hit a bump and not impact the other, the suspension was tough and didn’t ride bad, but it didn’t take long for owners of Fords to find out that reduced tire wear was not one of the advantages. In fact, tire wear was an issue as was the tendency for the trucks to wander and follow seams in the roadway, particularly when the shocks were worn.
Over the years, we’ve had a love/hate relationship with the front end under our F-350. On the plus side, not much maintenance has been required. Other than regular lubrication, all that’s been done was a set of kingpins and a complete set of tie-rod ends at the 160K mark. On the other hand, it has had a tendency to knock the corners off a set of tires in short order, particularly when the shocks were shot, which happened with alarming regularity. Over the years, we’ve learned that the secrets to preventing premature tire wear were regular alignments and fresh dampers.
Springing in stock form on...
Springing in stock form on our F-350 was via some stout coils. The original axles are forgings with a small amount of drop.
While the twin I-beam suspension is a mixed bag of good and not so hot for Ford aficionados, it really leaves a lot to be desired when altitude alterations are part of the plan. Raise or lower a truck with stock axles much past factory ride height, and the camber becomes such that you’ll be saying goodbye to the edges of your tire’s treads in no time. With Ford’s single solid axle predecessors, there have always been a number of options to get the front end down, such as modified stock or aftermarket dropped axles or getting rid of the stock front suspension entirely and replacing it with a custom-made independent or a clip. For many of the twin I-beam trucks, most of the same options exist (although we’re not aware of anyone dropping stock axles) as dropped replacement twin I-beams are available and there are a number of custom independents and clips that are suitable for F-150s. But in the case of an F-250, and certainly our ’73 F-350, load capacity becomes an issue with aftermarket IFS and passenger car clips, so, as far as we were concerned, the only option was to install dropped axles—and that decision led us to Airbagit.com.
The axles are positioned by...
The axles are positioned by radius arms attached to the frame with rubber biscuits. Note the tire rod passes between the legs of the arms.
The stock axle compared to...
The stock axle compared to the dropped replacement from Airbagit.com/Chassis Tech
We were impressed with the...
We were impressed with the construction of the axles. Machined from solid steel the ends for our F-350 had additional support at the tops and bottoms of the kingpin holes for increased strength.
At the inner ends of the axles...
At the inner ends of the axles are urethane bushings
With the stock axles removed...
With the stock axles removed the next to go were the spring towers. The tops of the towers were cut off with a torch so we could get to the welds that secured them to framerails with a cutoff wheel.
The original right side axle...
The original right side axle bracket (that attaches to the left frame rail) required some minor trimming to fit inside the new bag bracket. The pre-punched holes lined up perfectly with the holes in the frame so we knew the axle bracket was in the right spot.
To fit flush against the frame,...
To fit flush against the frame, the new left side air bag bracket required a small notch to clear the steering gear. It was filled in with a small patch.
Here, the new right side air...
Here, the new right side air bag bracket and the axle mount have been welded and bolted in place. The holes in the bag brackets were used to make plug welds to the frame.
The left side bag and axle...
The left side bag and axle brackets are permanently mounted. The small patch over the notch for the steering gear doesn’t interfere with the air bag.
We used the Denominator II...
We used the Denominator II airbags, and with the suspension at ride height the bags were slightly below the optimum installed distance between the mounts. We could have left everything alone, but chose to modify the mounts.
The top plates were cut off...
The top plates were cut off the axle mounts then threaded rods were used to position them at the proper installed bag height. Next, the lower parts of the mounts were trimmed to fit and welded back together.
Our modified mounts position...
Our modified mounts position the bags perfectly. In most cases, modifications aren’t necessary but we’re working with a unique application.