Why Does A Full-Float Axle Matter So Much?

[JLUR Farout]

Hello,
I have owned a Chevy 1500, a 2500, a Frontier, an F350, a Ram 2500, and many other vehicles. All those trucks had conventional rear axles with the bearings inside the axle tubes and towed so much more. I get the ease of servicing for having a unit bearing on the outside of the axle tube, so you don't have to tear the differential apart to service. But how does it make a difference in towing capacity? Have the axle tube walls just been too thin all these years? I presumed the weight restriction of 3,500 lbs was due to wheel base, frontal area, and suspension sag from soft springs.

NEW HEAVY-DUTY
FULL-FLOAT DANA®
REAR AXLE
A common aftermarket upgrade, full-float axles are now available on Wrangler for the first time ever. Standard on all Rubicon models, the new Heavy-Duty Full-Float Dana® Rear Axle consists of a wheel hub assembly that is separate from the axle shaft, with a spindle bolted to the axle tube that supports the wheel hub via a pair of wheel bearings. This stronger, more robust full-float construction enables a maximum towing capacity of 5,000 pounds( Disclosure8) on 4dr Rubicon 3.6L automatic and 4dr Rubicon 2.0L automatic

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[me109stock]

I'm not a mechanic, but... In a full float axle the axle shaft only drives the wheel, it doesn't drive and support the wheel. Bearing surface and size is also larger on a full float axle spreading the load over a larger surface. The other benefit for off-roading is if you snap an axle shaft your wheel may not drive anymore, but it stays on.

 

[Zandcwhite]

Hello,
I have owned a Chevy 1500, a 2500, a Frontier, an F350, a Ram 2500, and many other vehicles. All those trucks had conventional rear axles with the bearings inside the axle tubes and towed so much more. I get the ease of servicing for having a unit bearing on the outside of the axle tube, so you don't have to tear the differential apart to service. But how does it make a difference in towing capacity? Have the axle tube walls just been too thin all these years? I presumed the weight restriction of 3,500 lbs was due to wheel base, frontal area, and suspension sag from soft springs.

NEW HEAVY-DUTY
FULL-FLOAT DANA®
REAR AXLE
A common aftermarket upgrade, full-float axles are now available on Wrangler for the first time ever. Standard on all Rubicon models, the new Heavy-Duty Full-Float Dana® Rear Axle consists of a wheel hub assembly that is separate from the axle shaft, with a spindle bolted to the axle tube that supports the wheel hub via a pair of wheel bearings. This stronger, more robust full-float construction enables a maximum towing capacity of 5,000 pounds( Disclosure8) on 4dr Rubicon 3.6L automatic and 4dr Rubicon 2.0L automatic

The 1500 and the frontier were both semi-float. The JLU was always under rated towing wise in America. Australia and Europe both got 5500lb tow ratings even with the semi float axle. I think it was as much politics as anything else. The WJ grand Cherokee was rated to tow 6500lbs with a shorter wheel base, unibody, and similar but weaker axles as the center sections were cast aluminum.

 

[Jank4AU]

 

[rcadden]

Advertised tow capacity factors in more than just the weight they can pull. There's also stopping power, etc.

Having towed a 3500lb camper behind my JLU once, it's not something I ever want to do again, personally. I got like, 10 MPG, and it felt like it would be extremely easy for that trailer to start driving me, especially the few times I had to hit the brakes.

 

[grimmjeeper]

Hello,
I have owned a Chevy 1500, a 2500, a Frontier, an F350, a Ram 2500, and many other vehicles. All those trucks had conventional rear axles with the bearings inside the axle tubes and towed so much more. I get the ease of servicing for having a unit bearing on the outside of the axle tube, so you don't have to tear the differential apart to service. But how does it make a difference in towing capacity? Have the axle tube walls just been too thin all these years? I presumed the weight restriction of 3,500 lbs was due to wheel base, frontal area, and suspension sag from soft springs.

NEW HEAVY-DUTY
FULL-FLOAT DANA®
REAR AXLE
A common aftermarket upgrade, full-float axles are now available on Wrangler for the first time ever. Standard on all Rubicon models, the new Heavy-Duty Full-Float Dana® Rear Axle consists of a wheel hub assembly that is separate from the axle shaft, with a spindle bolted to the axle tube that supports the wheel hub via a pair of wheel bearings. This stronger, more robust full-float construction enables a maximum towing capacity of 5,000 pounds( Disclosure8) on 4dr Rubicon 3.6L automatic and 4dr Rubicon 2.0L automatic

F350s have only come with full float axles for decades. Even the F250 hasn't had a semi-float axle since 1997. How old was the F350 you had?

To answer your question, the full float axle can carry more weight. More axle weight capacity means more tongue weight capacity. More tongue weight capacity means more trailer weight capacity (assuming the rest of the vehicle is up to the task).

 

[grimmjeeper]

The 1500 and the frontier were both semi-float. The JLU was always under rated towing wise in America. Australia and Europe both got 5500lb tow ratings even with the semi float axle. I think it was as much politics as anything else. The WJ grand Cherokee was rated to tow 6500lbs with a shorter wheel base, unibody, and similar but weaker axles as the center sections were cast aluminum.

Europe restricts towing vehicles to 100 KPH (62 MPH). The slower you go the safer it is to tow heavier loads.

 

[Ratbert]

The 1500 and the frontier were both semi-float. The JLU was always under rated towing wise in America. Australia and Europe both got 5500lb tow ratings even with the semi float axle. I think it was as much politics as anything else. The WJ grand Cherokee was rated to tow 6500lbs with a shorter wheel base, unibody, and similar but weaker axles as the center sections were cast aluminum.

Tow limits can be significantly higher when it's illegal to tow at higher speeds.

 

[Zandcwhite]

Europe restricts towing vehicles to 100 KPH (62 MPH). The slower you go the safer it is to tow heavier loads.

CA restricts us to 55mph, under that same logic I can throw 7klbs behind the JLU...

 

[Ratbert]

CA restricts us to 55mph, under that same logic I can throw 7klbs behind the JLU...

If the rest of the county followed suit then yes, our limits would logically be increased.

I'm not sure where you got that 7k number though. As far as I can tell JLUs are still limited to 3.5k since apparently nobody has seen one with a 5k limit.

 

[Black Bear]

It’s seems like everyone is an expert on axles and towing all of the sudden. The argument was always about suspension and it’s off-road capabilities now it’s about the axles. People chime in that have little to no experience and now it’s the semi vs full float debate all because of Stallantis marketing in the name of competition. These vehicles underperform in every category except climbing rocks and we’ll never get a straight answer from them for liability reasons.

 

[Zandcwhite]

If the rest of the county followed suit then yes, our limits would logically be increased.

I'm not sure where you got that 7k number though. As far as I can tell JLUs are still limited to 3.5k since apparently nobody has seen one with a 5k limit.

Europe allows 5500lbs at 62mph, being that 55mph is slower and as you stated therefore safer to tow more weight I just threw out a number. 55mph being 13% slower than 62mph, if it's directly proportional then let's say 6200lbs...
Safe and legal aren't always the same thing. If a big rig pulling triples is safe at 80mph in Utah (is legal right), a sports car is safe in those same conditions at at least triple digits (but not legal).

 

[danba]

Advertised tow capacity factors in more than just the weight they can pull. There's also stopping power, etc.

Having towed a 3500lb camper behind my JLU once, it's not something I ever want to do again, personally. I got like, 10 MPG, and it felt like it would be extremely easy for that trailer to start driving me, especially the few times I had to hit the brakes.

Do you use a brake controller, weight distribution and sway control hitch? I do and I have no problems towing a 3500lb AS, except for lack of power on steep hills.

 

[Vinman]

Full floating axles have a much larger diameter outer axle bearing which allows it to carry more weight and with a FF axle, the shafts only purpose is to drive the hub.
In a semi floating axle, the shaft not only drives the hub, it has to also support the weight of the vehicle.

 

[6.2Blazer]

Hello,
I have owned a Chevy 1500, a 2500, a Frontier, an F350, a Ram 2500, and many other vehicles. All those trucks had conventional rear axles with the bearings inside the axle tubes and towed so much more. I get the ease of servicing for having a unit bearing on the outside of the axle tube, so you don't have to tear the differential apart to service. But how does it make a difference in towing capacity? Have the axle tube walls just been too thin all these years? I presumed the weight restriction of 3,500 lbs was due to wheel base, frontal area, and suspension sag from soft springs.

I've never seen a F350 that did not have a full-float axle, and haven't seen a Chevy 2500 or Ram 2500 in a long time (like 20 years?) that did not have a full-float axle. On these full-float rear axles I wouldn't call it a unit bearing design either. They typically had a pair of removable/serviceable tapered wheel bearings inside a hub assembly.
As already mentioned, on a full-float axle the axle shafts do not support the weight of the vehicle and load, therefore no bending force on them. The only purpose is to provide power/torque/rotational movement to the tires. The hubs and bearings supported all the weight with no impact to the shafts. On a semi-float axle the axle shafts provide both the torque to rotate the tires AND support the weight of the vehicle. This means a semi-float shaft has a lot more overall stress on it. The wheel bearing capacity is also a factor. On a full-float axle the wheel bearings are are further outwards and more centered in the tire, meaning a more direct loading.
Semi-float bearings are inside the axle housing meaning there a lot of leverage on them as the tire sticks out further from them. There is also some safety factor involved here. If you break an axle shaft on a full-float axle it does not really affect the handling or load capacity of the vehicle. If you break a semi-float shaft it can cause all types of weird behaviors and potentially even allow the tire to completely break away from the vehicle. You will trash the wheel bearing on a semi-float axle if you break a shaft and keep driving.

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