We've said it before, still it's worth repeating-when it comes to building a hot rod, if anything seems simple, you're overlooking something. A case in point is filling a dropped axle. A traditional trick, when dropped axles first appeared it wasn't at all unusual to box, (what became known as filling) the section of I-beam between the spring perch and kingpin holes as a means of reinforcement.
Filled axles came about because not everyone dropping them in the early days had a complete understanding of metallurgy, so as a result the factory heat treatment was often destroyed in the process and strength was sacrificed. More than a few hot rodders found that their newly-installed dropped axle would undergo an unwanted camber change after hitting a pothole or two, or the car would have a navigational mind of its own under hard braking when the ends of the axle would twist. Filling the ends of axles usually solved these problems but, like many things that are done to improve the performance of a hot rod, there was a cosmetic benefit to boot. Necessary or not, filled axles looked cool and added that no-nonsense, purposeful look to the frontend; filled axles meant you were a player (of course, if the ends of the axle were filled and the center was full of holes, you were a serious player)
Like many traditional touches, filled axles are back in style. Thankfully, with the aftermarket cast-and-forged dropped axles available today, filling the ends isn't necessary from a strength standpoint, it's purely cosmetic. However, we've seen it done lately in such a manner that strength of the axle is actually compromised-how's that for irony? Just as dropping an I-beam without negating the heat treatment takes know-how, so does filling the ends; it's much more complicated than simply welding plates to the axle.
Two guys who know exactly what's involved in the process of filling an axle are Dennis and Matt Lesky, of the Ionia Hot Rod Shop (Ionia, MI). Dennis retired from GM and is a card-carrying journeyman tool and die welder and son Matt has background as a machinist and fabricator that began when he was a scout. These guys know a thing or two about working with metal, and a few of the things they know are that axles have to be preheated before and during the welding process, the correct welding rod is necessary, and the rate of cooling has to be controlled afterwards. It's a process that isn't as simple as some think, but the results are worth it. Take a look a see how it's done.
Here's the ultimate traditional...
Here's the ultimate traditional dropped axle, as done at the Ionia Hot Rod Shop- its been filled and drilled while the radius rods have been drilled and sleeved. They do it all, from complete turnkey cars to filling and drilling axles.
The first step is to remove...
The first step is to remove all paint and contaminants and thoroughly clean the axle ends.
Filler plates are cut from...
Filler plates are cut from mild steel. Because of slight variations in the axle ends side to side and front to back, it's not unusual for each one of the four plates to be fitted individually.
The goal when fitting the...
The goal when fitting the filler plates is to make them fit flush with the edges of the axle to reduce the amount of grinding required after welding.
Before any welding is done,...
Before any welding is done, including the initial tacks, the axle should be preheated. One way to ensure the preheat is sufficient is to use a "heat stick" marker that changes color at a prescribed temperature; another option is an infrared heat sensor.