Last time in our series on axles, we took a long hard look at the axle splines along with the overall shape of the component. And before that, we looked at materials and tempering. This time around, we’ll look at the flange, housing ends and lightweight options.
The flange on an original equipment axle typically measures 0.375-inches in thickness. Wheel studs are of the press-in variety (with a knurled shank) and usually measure 7/16-inch (small GM and select early Mopars) or ½-inch (the rest). Later model cars will usually be fitted with metric studs, but again, they’re of the press-in variety. An aftermarket axle will usually have a thicker flange. It will be (most often) drilled and tapped to accept ½-inch diameter screw-in studs. Quality race axle will be setup for 5/8-inch diameter drive studs (that’s another story altogether).
What type of axle retention is required? Mark Williams points out that the majority of race-sanctioning bodies require some form of positive axle retention. The original equipment C-clip (which fastens the axle on the inboard side at the very end of the spline) does not meet these requirements. Accordingly, MW offers a special bolt-in C-clip eliminator kit that provides the necessary retention. If, on the other hand, you plan on narrowing the housing, it’s a good idea to change the housing ends. Weld-on aftermarket housing ends provide for a much larger (stronger) bearing, provide for positive retention by way of a hefty retainer and they can be mated to most popular brake applications (ranging from OEM drums to aftermarket disc brakes).
So far so good, but what housing end should you choose? It’s best to match the housing end to the brake package you plan on using. If you’re using aftermarket disc brakes, it’s best to work with something like a symmetrical housing end. The reason is it allows you to use a high quality brake system (disc). Williams notes that he does not recommend the use of small Ford housing ends. The wheel bearing is too small and delicate.
If you’re a racer, the final consideration is weight. Here’s why: A set of lightened axles from Mark Williams can reduce weight by at least 9-1/2 pounds (depending upon the length of the axles and the type of rear end they’re going into). As an example, one standard M-W axle for a typical S/S car weighs 17.3 pounds. The same axle in a M-W Super-Light configuration weighs 12.4 pounds. How is axle weight reduced? The first place is a “gun” drilled axle. Using Mark Williams’ pieces as an example, the core of the axle shaft is bored 11/16-inch, to resemble a gun barrel. As you can well imagine, this requires special machine tools, but M-W takes an extra step in the process (which is seldom, if ever done by other companies): They precision hone the gun drill bore to remove tooling marks on axles produced from 300M steel. The gun drill found on the 4340 axles is actually smooth. Now, this might seem like a small step, but the honing process actually improves the strength of a gun-drilled axle. Whenever M-W gun drills an axle, they also include round lightening holes in the axle flange. These two steps reduce axle weight by 17% over a standard axle.
If you’re really serious about reducing rear end flab, then you can look at the “Super-Light” 300M pieces available. In this case, the gun drill bore is increased to 7/8-inch (and of course, honed). Additionally, the axle flanges are extensively milled. While you can’t see it on a complete axle, there’s also extensive machining behind the M-W nameplate at the end of the axle coupled with a revised axle profile. These machining operations can result in a weight savings of 29% over a standard gun drilled axle. Typically, this machining is done to 35 spline axles for use on cars up to 1800 pounds and on 40 spline axles for cars over 1800 pounds.
If you do some digging, you might find what seems to be a wee contradiction to those weight removal “rules.” For example, we once had a set of 12 bolt axles “lightened” for a legal NHRA Stocker. They were 35 spline models destined for use in a 3,000-pound car. These axles had what initially appeared to be “Super-Light” modifications. There’s a catch: For an application such as this, M-W uses the standard 11/16″ diameter gun drill process matched with the extensive pocket milling on the flange. It doesn’t provide quite the ultimate weight savings of the Super-Light axle, but it’s very close.
That wraps up our look at the mechanics of axles. In the next issue, we’ll take a look at measuring a housing for aftermarket axles.