Jim Smart
October 17, 2012

The term "full-floater" isn't widely known in street performance circles. However, it's a term that drag, off-road, and most prevalently, circle track racers are very familiar with. As auto enthusiasts continue to extract more and more performance out of their vehicles, both from a power level and a usage standpoint, the need for more heavy-duty support equipment is growing. Companies like Speedway Engineering, which normally exist to provide professional race teams the highest quality and most cutting-edge products, are filling the need of hard-core enthusiasts that are pushing their projects to the limit and beyond. The full-floater rearend is just such a component--one that has been showing up on a number of open track and autocross-capable machines.

Speedway Engineering manufactures full-floating, custom 9-inch rearends for just about any vintage street/race Ford or Mercury you can think of. Considering the abuse we intend to put our '66 Mustang fastback project, Colt of Personality, through, we called Speedway to have them build one of their fine pieces for our filly. In this article, we'll cover the reasons why you may need a full-floater rearend for you ride, and we'll show you a glimpse of Speedway's fabrication process--much of it includes guarded proprietary secrets that we can't show you.

Founded by Frank Deiny Sr. in 1964, Speedway Engineering provides precision-manufactured chassis components and rearends for race cars in everything from your local circle track right up to NASCAR's Sprint Cup. People make their living with these parts, so quality and the latest technology is of the utmost importance. In more recent years, Speedway has been thriving under the direction of Ken Sapper, who has kept a steady eye on what racers and street enthusiasts want for their high-performance rides.

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Full-Floating Filly

There are plenty of us with classic Mustangs who have stepped up to the glory of a 9-inch Ford rear axle after suffering the failure of an over stressed 8-inch peg leg. There's greater confidence with a 9-inch Ford thanks to a rugged four-pinion design and beefier components. What's more, you can upgrade it to 31- or 35-spline axles, locking differential, brute third member, big disc brakes, and more.

A conventional 9-inch rearend is known as a semi-floating axle because, though axles float, they also carry vehicle load via the axle bearings and housing. Full-floating, as the term implies, means that the axleshaft doesn't carry vehicle weight--hubs and axle housings do. Why a full-floating axle housing for your vintage Ford? For the same reason they're installed in trucks and race cars--better load distribution without axle stress. Believe it or not, full-floating drive axles aren't just for racing. Heavy-duty 3/4- and 1-ton truck drive axles have been full-floating for ages because they manage load better than a conventional axle with less stress. The same can be said for race cars with full-floating drive axles.

The axleshaft, which is splined into both the differential and drive plate, transfers power to the wheel without having to shoulder vehicle weight. Drive plate selection depends on what you want the vehicle to do, as you can add camber and/or toe to the solid rear axle by using a crowned axle and the matching steel drive plate. Speedway Engineering's axles are made from high-grade premium alloy steel. Once they are CNC-machined to strict specifications, they're heat treated and double tempered to ensure durability. Once heat treated, these axles are polished for a smooth fit. Axle selection depends on what you want your ride to do.

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In addition to building in extra camber, there's also the added benefit of reducing brake knock back. Brake knock back is when the axleshaft flexes or moves under cornering and the axle movement then pushes the brake pads outward, moving the brake caliper pistons into the caliper. When you come to the next corner and hit the brakes, there's nothing there for a brief second or two, but depending on your speed into the corner, that can be enough time to put you off track or worse. While knock back is more prevalent in C-clip-style axles, it can occur in 8- and 9-inch rearends when the axleshafts become weak over time, often from the axleshaft supporting the load. In the case of a full floater, the brake package is fixed to the hub, so there is no movement.

For a competitive road race car, knock back can be costly over the course of an event, and while we won't be competing for any road racing championships with our project Mustang, we certainly don't want any braking surprises during a high-performance driving event or similar outing.

Speedway Engineering's full-floating 9-inch axle assembly consists of a custom-made axle housing designed specifically for full-floating axles. The axle's center section is CNC-machined to ensure concentricity at each of the bearing bores to reduce or eliminate stress issues. At each end are extended-length snouts, which prevent tube crush and provide good bearing/hub support. Under the close supervision of Frank Ferrell, Welding Manager at Speedway Engineering, these handcrafted housings and components are precision manufactured at the company's Sylmar, California, facility for your specific application, and based on information you provide.

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Is A Full-Floater For You?

We have to admit, this is the first time we've ever been presented with the opportunity to install a full-floating axle in a Mustang. What this has meant for us is the chance to learn something about race-ready axle technology. The beauty of a full-floating 9-inch Ford is its industrial strength demeanor--engineering that takes Ford's bulletproof rearend to a new level. Full-floating technology isn't for everyone and it can get expensive. For durability, easy service, flexibility, and the ultimate form of load distribution as we know it today, Speedway Engineering has the goods for brute street and racing performance.

Build any 9-inch housing you desire because there are four to choose from--Super Light NASCAR Style, Short NASCAR Style, Saturday Night Late Model, and the vintage Ford rounded 9-inch (1957-1966). Choice depends on how you're going to use your Speedway Engineering housing. With the exception being the rounded back, it's challenging to tell the difference, but important to know about when you order.

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Float For Your Hard-Earned Buck...

  • CNC machining throughout
  • Cooler, vent, and drain fittings
  • 3.0-inch diameter 0.250-inch wall axle tubes
  • V-notched welded seams
  • Laser cut truck arm pads and brake brackets
  • Longer end snouts
  • ARP housing studs
  • Every housing guaranteed plus or minus 0.003-inch toe and 0.03-degree camber
  • Complete assemblies are shipped with specification sheets that include camber, toe, width, pinion offset, and angle
  • Complete assemblies include housing, hubs, hub bearings, seals, nuts, drive plates, dust caps, O-rings, and axles
  • Wheel studs
  • Trailing arm mounts are located to fit the most popular frames
  • Each assembly is made to order though there are popular types in stock
  • Choose Your Center Section

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21 Hanging upside down in the paint booth, our new Speedway Engineering 9-inch housing is ready for paint (or powdercoat if you prefer). Be sure to check back as we stuff the 9-inch with a stout third member and add Wilwood's trick full-floater rear brake system.