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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