Deep Dive: The Full-Floating Rear Axle, Explained


Deep Dive: The Full-Floating Rear Axle, Explained


It’s no secret that original factory parts are usually a compromise. When faced with the challenge of making components that are strong enough but as cheap as possible, automakers tend to cut corners. One of the best examples of that is in rear-axle assemblies — you can pretty much count on factory rear-ends having just barely enough strength to do the job they were designed for. Run any more power than that through them, and you’re just begging them to fail.

Axle bearings are a particularly weak point in factory rear ends, including the Ford 9-inch. Even though this time-honored rear end is now considered the standard for modern high-performance aftermarket rear-axle assemblies, its basic design does have some compromises. As with most other factory rear ends, the 9-inch’s axles have to not only bear the entire torsional force of the engine’s power, they also have to support the weight of the vehicle and cope with any side loads from cornering.

FordFest - Foxbody Mustang Autocross

While the average autocrosser might not need the benefits of a full-floating rear axle, if heavy and fast corner-carving is in your future, it certainly is something to consider.

This compromises the strength of the axles. And in certain applications, it can even bring such dangers as brake failure at high speeds. Fortunately, the aftermarket has once again developed an effective fix. This solution, called a full-floating rear end, relocates the axle bearings to a hub mounted to the axle housing, allowing the axles to do essentially nothing but transmit power to the rear wheels.

It’s a simple concept, and it’s been used in the heavy-duty truck industry for decades. But there are a lot of nuances to full-floating rear-end setups. To explain these systems and how to decide if you need one for your vehicle, we spoke to Lucas Hardin of GearFX. This company has built a reputation for brutally strong rear ends, in particular the Ford 9-inch. Their advice is as good as gold for anyone looking to get the right rear end for their performance car.

DSE C7 Full-Floating Hub Design

There are different designs to full-floating hub bearing designs. Detroit Speed offers designs based on the C6 or C7 mount design, as seen here.

“With factory rear-axle assemblies, the axle shaft is not only supporting the weight of the vehicle, but it’s also taking the rotation of the driveshaft and the ring and pinion, and pushing it out to the wheels,” says Hardin. “Because of that, the axle bearings are doing a lot. And then on C-clip setups — like a factory Ford 8.8-inch or a GM 10- or 12-bolt — the C clips are also doing a lot. But with full-floating axle shafts, the axle shafts aren’t bearing any sort of load for the vehicle. Instead, the hubs are handling all of the sprung weight of the vehicle. And when you go around a corner, those hubs are taking all of the side loads too.”

Besides putting less strain on the axles, and thereby allowing them to handle more power, full-floating setups offer several other key advantages, making them well worth considering for your car.

Check Out More Detroit Speed Full-Floating Parts Here

Want to learn more about full-floating kits from Detroit Speed? Click on the image to the left to see more!

Less Strain on the Bearings

Full-Floating Rear Axle Assembly

GearFX shop foreman Rob Knipp begins final assembly of a Baer Brakes Tracker full-floating hub assembly. This system uses tapered roller bearings, similar to what many vehicles use on the front spindle. This is a strong setup, but does require more maintenance than a Corvette-based full-floating hub assembly.

In much the same way that traditional non-floating rear ends force axles to do double duty, they also demand that bearings handle a number of different tasks too. And, as is the case with axles, this multitasking arrangement forces compromises that can cause issues in performance applications. Full-floating rear ends minimize this tendency, allowing bearings to survive better in hard use.

“With a C-clip axle setup, you have axle bearings that support the end of the axle shaft,” says Hardin. “You’ve got an axle shaft that goes all the way in, and then you’ve got C clips that hold that shaft in. And on a semi-floating axle, the axle bearing is doing all that work instead. So it’s supporting the weight of the vehicle, and it’s also keeping the axle from moving in and out.”

With a stock C-clip or semi-floating axle assembly, the bearings are doing a lot of work, which can cause premature failures and other issues. Full-floating systems eliminate these problems.

Improved Brake Stability

For some applications, a full-floating rear-end assembly isn’t just a matter of maximizing component strength. It can also be a valuable safety measure, by ensuring consistent brake operation.

“When doing really aggressive high-speed cornering — like road-racing guys that are pulling over 1 g on the skidpad — you can get brake-pad knockback,” says Hardin. “With typical ball bearings on non-floating rear ends, there’s no preload on the bearings. So the axle shaft will start moving in and out slightly. And when that happens, it pushes your brake pad back into the caliper. So if you go around a really hard corner, you may get to the next corner, hit the brakes, and your foot goes to the floor, because you’ve got to push the piston back out to be able to squeeze the pads on the rotor. It’s very scary.”

Easier Servicing

In addition to the performance benefits they offer, full-floating setups make the whole rear-end assembly much easier to service. “With a full floater, you don’t have to pull the axle shafts out and risk anything leaking severely,” says Hardin. “You just pop the axles out, and then you can pull the center section. If you do it right, you don’t even have to take the wheels, tires, and brakes off.”

With the faster, easier servicing a full-floating system allows, some car owners even use their 9-inch like a quick-change rear end. “We’ve got a road-racing customer who drives a Panoz that has a full-floater setup,” says Hardin. “He has cases with three or four different gear ratios that he swaps around depending on what course he’s going to be on.”

Who Needs A Full-Floating Rear Axle?

So with the compelling advantages a full-floating rear-end offers, the big question becomes, do you need one? Well, that depends.

Full-floating rear ends are a better design than the factory setup. There’s no question about that. But, like most things in the performance world, it comes at a cost — typically about $2000 higher than a comparable non-floating rear end. So should you invest the extra money?

For extreme drag competitors like Pro Mods, a full-floating rear end is a no-brainer. Those cars punish their drivetrain with so much power that it’s an obvious advantage to relieve axles of the burden of carrying the vehicle’s weight. But, outside of those top classes, most drag cars simply don’t need a full-floating rear end — a well set up traditional rear-axle assembly can be more than adequate. And so, for the most part, the folks that really benefit from a full floating setup are guys turning corners hard and fast, such as in road racing or intense autocross.

Because full-floating rear ends are such a benefit to those who venture onto road courses, they’re enjoying increased popularity these days, with the recent boom of pro-touring cars. For them, full-floating setups are a natural. But even so, the majority of pro-touring cars don’t routinely reach a level of performance where they need one, says Hardin.

“It’s still kind of a niche thing. Most pro-touring cars are maybe going to Good Guys once a year. They’re going to run it around the autocross course, and they’re going to be happy with it. All other times, their car will be driven on the street. But where full floaters really make sense is when guys are doing all of the Good Guys events, not just the one that’s local to them. Those guys will typically pony up for a floater.”

Choosing A Full-Floater Setup

Full-floating rear-axle systems mount to unique ends welded onto the rear-end housing. And so, they can be fitted to any rear end you want to run, including Dana 60 and GM 12-bolt. That said, the most common rear-end to have them on is the Ford 9-inch, for the same reasons they’re used on just about any type of performance car — strength, versatility, and widespread aftermarket support. “It goes back to all the things that make the 9-inch so great,” says Hardin. “It’s an all-around better option if you’re going to invest an extra $2,000 on a full-floater setup.”

Aside from the type of rear-end you want to run, the other choice you’ll face is which type of floater system you want to run, which dictates the type of brakes and hubs you’ll be working with. The most popular system for GearFX’s customers is the company’s Corvette-style setup.

This system uses Detroit Speed housing flanges that allow you to use C6 or C7 Corvette sealed-wheel-bearing hub units. It has the advantage of being able to use Corvette ABS wheel-speed sensors if you want. It’s also somewhat simpler — it doesn’t use tapered roller bearings like some other floater setups, meaning you don’t need to have provisions to get oil from the case to the wheel bearings.

GearFX Full-Floating Assembly Axle 1

Now the axle shaft is installed. Notice the O-ring at the end of the axle shaft that is designed to help keep grease in place. Once the axle shaft is seated, the dust cap will finish off the installation.

The downside to the Corvette/Detroit Speed setup is its additional cost. The housing flanges are similar in price to those of other floater systems, but you’ll still have to buy the hubs, spacers, axle shafts, and other OEM GM parts. It all adds up quickly to make it more costly than some other full-floater systems.

The next most popular setup is the Baer system. This uses tapered roller bearings — essentially like a front-wheel hub, but there’s an axle shaft in the middle. The advantages of this arrangement are that it’s even stronger than the Corvette setup, and you can use bigger brakes. It’s essentially more like a NASCAR system. On the downside, the tapered roller bearings used on this setup typically require more maintenance.

Regardless of whether or not a full-floater setup is essential, many car builders nowadays are adding them to their rear end simply for the peace of mind they offer. Yeah, maybe it’s overkill for some cars, but the plain fact remains that it’s a better, more robust arrangement for any rear-axle assembly. If nothing else, a lot of car owners like full-floating setups simply for how much easier they make it to service the rear end or swap out the differential assembly. “There really aren’t any drawbacks to a full-floater,” says Hardin. “It’s going to be the better option every time.”


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