These Guys Drop Hot Rod Axles the Old Fashioned Way

30 Sep.,2022


drop axle for sale

Early on in the evolution of the archetypal hot rod, builders and drivers alike understood the benefits of having a dropped front axle. Not only did the reconfigured piece lower the center of gravity up front, giving the car better handling characteristics, it also cut wind resistance and added a slight rake to the rod's profile. This drop modification completed the "looks fast standing still" styling that many of the world's greatest hot rods employ.

With demand increasing these days for period-correct hot rods, the need for dropped axles has risen accordingly. And, yes, they are available new from retailers. Companies like the So-Cal Speed Shop and Speedway Motors will sell you a brand-spankin'-new axle in several configurations and drops for your build. But interestingly enough, there are still a few artisans out there doing it the old-fashioned way, taking a factory axle and bending it to shape with heat and pressure.

It's not something you master overnight. Dropping an axle safely takes knowledge, skill, patience, and the right tools. Andrew Kohler of Kohler Kustom in Cogan Station, Pennsylvania, has been schooled in the art of properly dropping a vintage axle, performing drops for major hot rod builds all across the globe. Using the press his grandfather built, he performs drops on straight axles harvested from cars of the glory years of hot rodding, right there in his old-school shop deep in the northern Pennsylvania woods.

Here, Andy and good friend Matt MacGill take on a stock '33-'36 Ford axle, showing us first the process of picking out a good example to drop, and second, bending the piece safely and properly to achieve a consistent drop. Once installed, our axle will help get our front end low and level, and get our ride looking and performing the way a true hot rod should.

Check your potential axle carefully and make sure the perch and kingpin bores are not worn, cracked, or out of round. While damage can usually be repaired by sleeving the bores, it is a costly procedure. Unless the axle is a coveted 1932 piece, it's likely a better choice to find an axle that has good bores to start with. If you're hunting axles at a swap meet, you can bring a good kingpin with you to give potential candidates a quick check on the kingpin bores. Visual inspection is done by sighting down the top of the axle to check for bends or twists. If it is just bent in one plane, the axle can be easily corrected, but a twist is a more difficult, time-consuming repair, especially if it is spread out across the whole axle rather than localized to one area. The axle in photo A is twisted across its entire length, over two spatial planes. Leave this one in the pile, as it would be hard to straighten out. The axle in photo B looks quite distorted, but it's just bent in one plane (front to back). A few minutes in the shop press and this one will be straight and ready to drop.We've picked our axle, a nice, straight one from the 1933-1936 period, so now we can pre-check the alignment to make sure we don't have to correct it during the drop. The axle is set up level front to rear and side to side, and spare kingpins are set in the ends to measure from. Andrew checks the kingpin inclination (KPI) angle since this measurement will determine the camber angle. He shoots for 0 degrees camber, as factory spec range is +1 to -0.5 degrees. By arranging our drop height shims higher or lower at the rear, we can correct potential KPI issues during the drop process. With a KPI reading of 7 degrees, we are dead-on to factory stock and won't have to adjust it at all.The caster is also checked, as we want a 0-degree reading on both sides here. The 2-degree angle reading matches the 2-degree perch angle, giving us a final 0-degree difference. Once again, we are within spec and are ready to roll.

Kohler's axle jig is built from heavy I-beam and thick-wall rectangular tubing. It fits into his shop press and can accommodate any early Ford passenger or half-ton pickup axle from 1928-1948. One side holds the axle end that is to be dropped and the other end has an upright track that a special-made carriage (that bolts through the perch bore) rides on. This system limits how far the axle can narrow during the drop process.Kohler uses a stock Ford solid kingpin to secure the end to be dropped. It is replaced about every 10 drops or so.Shims are stacked below the perch bore area until the desired drop height is achieved. Kohler uses a special piece that he turned on the lathe specifically to fit inside and over the surrounding perch bore to use as a pushing surface. This unique piece protects the axle top from potential damage from the ram post.This axle will be dropped 2 inches over stock, so shims are stacked under the perch bore until there are 2 inches of space below the axle.Since the axle's KPI measurement checked out, we want to maintain that angle and keep it consistent. Shims are stacked at the rear end of the jig under the carriage until the measurement is also 2 inches. We want the rear of the axle to come down exactly the same height as the front. This will keep the KPI the same as before it was dropped. By changing the number of shims at the back under this carriage, the KPI angle can be changed during the drop.The heating process is what allows Kohler to work the mass of these thick, forged axles into a dropped shape. It also has a great deal to do with the overall appearance of the finished product. There are no fixtures used to control the shape of the drops; Andrew simply focuses the heat in different areas during certain points of the drop process to control the shape. There is a bit of an art to this aspect of the job, and it's something that takes time to learn. Generally speaking, you want to heat the whole area between the perch and kingpin bore, keeping at least an inch away from the bores with the flame, as you don't want them to distort during the drop. You also don't want to overheat the axle, as this can cause cracks to form. It should always be kept cherry red to dull orange. Bright orange or yellow is too hot! Safety equipment is a must. Andrew is wearing torch glasses to protect his eyes. He also recommends safety goggles or glasses for the press operator.The area to be dropped is evenly heated on both sides. Andrew will make one pass across the top and bottom of the web with the torch and move to the other side, alternating this process to keep the area at a constant temperature.Matt starts to apply pressure slowly and carefully, allowing the press and heat to do all the work. He also has to keep a watchful eye on the carriage to make sure it comes down straight and evenly, seating properly on the shims below it.As the axle starts to come down, Andrew continues to heat it with the torch, moving from side to side, keeping it evenly heated.Matt continues to add pressure with the press. At several points during the drop, he will release pressure entirely and allow the axle to "slide" a bit as it narrows during the drop. This is a slow process; Andrew and Matt let the press and heat do the work, maintaining the heat and gently applying pressure as the axle gives way to the ram.

Here the dropped shape is forming about halfway through to the finished drop height. At this point, Andrew changes the heating process a bit to "steer" the drop into an aesthetically pleasing shape.Matt releases the pressure to allow the axle to slide forward a bit. This reduces the side force on the ram and jig and makes for a smoother job all around. There's a lot going on here, and it illustrates an important point: Dropping an axle is not a one-person job. Andrew jokes, "I wouldn't think of dropping one by myself. Well, maybe if I had four arms and two heads." There are too many things to watch and be aware of for one person to do it safely.Kohler's axle jig is built from heavy I-beam and thick-wall rectangular tubing. It fits into his shop press and can accommodate any early Ford passenger or half-ton pickup axle from 1928-1948. One side holds the axle end that is to be dropped and the other end has an upright track that a special-made carriage (that bolts through the perch bore) rides on. This system limits how far the axle can narrow during the drop process.Success! The axle now has a beautiful, sweeping drop with no kinks or thin, overly stretched areas.The axle should cool slowly, with no attempt to quench it or hit it with shop air. Once it has turned completely gray, the pressure can be released and the retaining kingpin driven out. Note: Even though it's cooled down and grayed over, this baby is still piping hot. Andrew recommends a pair of heavy-duty insulated welding gloves when handling the axles.Once one side is done, it's time to remove the axle from the jig, move the carriage to the other perch bore, and load it to drop the other side of the axle. The same procedure is applied to the opposite side.It's important to keep the heating technique the same on both ends of the axle. If you don't, you risk having an axle with a drastically different look from one end to the other. After each axle is dropped, Andrew will level it, recheck all alignment angles, and inspect both drop areas carefully. If there are any inconsistencies or issues, they can be corrected before the axle is turned over to the customer.Here is a 2.5-inch dropped Model A axle on top, our newly dropped 2-inch 1933-1936 axle in the center, and a 2.25-inch dropped 1932 heavy-duty axle on the bottom. This new dropped axle has passed inspection and is now ready to ship to the customer.


Kohler Kustom