Hello All & thank you for your expertise.
I am in the market for a 13/14 F250 to tow a 8k pound fifth wheel rv. Sometimes our camping will be in open fields, so traction is a consideration. Could someone please explain in non-technical terms which axle choice (regular, limited slip, locking hubs) would be the best choice and why?

 

A differential splits power from the driveshaft and re-directs it towards a pair of wheels (one on the left and another on the right). The Super Duty trucks have at least one differential (rear). 4x4 models will have two (front and rear).

Standard (regular) differential construction freely allows the left and right wheel to turn at different speeds which is desired for making turns and maneuvering the vehicle. However, this comes with a compromise (traction). Under heavy power or slippery conditions (snow, ice, sand etc) then it's likely the standard differential will apply all the engine power to just one wheel and the other wheel will get none. The wheel with the least traction gets all the engine power which could quickly become a problem when off road or in slippery conditions (that wheel just spins and the vehicle doesn't go anywhere).

The solution to the above scenario is a limited slip differential. It has several small clutches inside the case that will transfer power to the wheel with better traction. When one wheel starts spinning, it 'grabs' the slower axle shaft and tries to turn it also. This helps with traction since you will have two wheels driving the vehicle instead of just one. Limited slip isn't a fully locking differential...it still slips in tight turns and slow speed maneuvering. The benefit comes when under heavy power or slippery conditions, so it's a good thing to have if you plan to venture off pavement or drive in inclement conditions. Limited Slip is fully automatic and does not require any operator input or switches to control.

A 4x2 pickup with standard diff will apply all engine power to whichever rear wheel has the least traction. The rear wheel with more traction will receive no power.

A 4x2 pickup with Limited Slip diff will have engine power split between both rear wheel (although it may not be 50/50 depending on the conditions).

A 4x4 pickup can drive around in 4x2 mode most of the time and the operator can choose to add engine power to the front wheels when desired. Those vehicles have a transfer case that routes some of the engine power towards the front wheels. In order for the front wheels to be driven by the engine, the hubs must lock. This can be accomplished automatically or manually depending on the features of your truck. This piece of equipment is called "Locking Hubs" which come in the automatic variety on the Super Duty trucks. Some owners remove the automatic hubs in favor of manually locking hubs for increased strength and dependability (sometimes the automatic hubs do not lock by themselves or quick enough...)

Newer trucks have another feature called Locking Differential. It's available on either a 4x2 or 4x4 truck and it mechanically locks the REAR axle shafts together so they spin at the exact same speed. Of course you would not use this feature on paved roads but it could be very handy when off road. I recommend you get the Locking Diff feature on your new truck and use it whenever you are in slippery conditions or when you think you might get stuck or need good positive drive power.

If you go with 4x4, the locking diff is more capable than limited slip because a locking diff will still transmit engine drive power to the wheels even if you are in a situation where a pair of wheels are in a low traction condition diagonally (front right and rear left or vice-versa). If you have a 4x4 with limited slip, then you could still have problems under this situation and will have to learn the 'riding the brakes' method to get yourself un-stuck.

I hope this helps.

 

Wow! An amazingly clear explanation! Thank you! I am certain your information will be read many times.

 

Glad to help. To add a bit on the locking hubs description....
Last I checked, Chevrolet/GMC 4x4 trucks come with automatic locking front hubs like Ford offers....however, the GM version does not have a manual over-ride (unless they added that feature recently). It's been a while since I've looked at new GM trucks so I am not 100% positive....

By contrast, ALL Ford Super Duty 4x4 trucks have the ability to manually lock the hubs in the event the automatic feature doesn't work or work quickly enough. Many times the truck has to move a few feet before the automatic hubs will engage which could be a real problem if you are already stuck in the mud. Ford provided a solution to allow the operator to manually lock the hubs in case the need arises. To lock the hubs you have to exit the cab and possibly trudge through the mud but at least you have the option when in need.

If you purchase a Ford (as you should...) and it's a 4x4 then you may consider removing the OE locking hubs in favor of something like Warn manual locking hubs instead. if so, then you'll have to manually lock and unlock the hubs every time. Just something to consider.

I keep my automatic hubs in good working order. Over the last 14 years there only has been a few times where I've needed to lock them manually. Most times I just let them lock automatically via the ESOF system (Electronic Shift On the Fly).

One more item.....
A 8k lb fifth wheel sounds awfully light. Many weigh much more than 8,000 lbs. Nothing against small trailers...I love small light trailers, they can pretty much go anywhere and get into pretty remote places. However, if you are going to be doing some serious off-roading then you are going to need a 4x4 and sometimes the fifth wheels can have clearance issues with the bed rails on some 4x4 trucks. My 4x4 is stock height and I still had to flip the axles on both of my fifth wheel trailers to get them to sit and tow level and have adequate bed rail clearance when off road. You may consider a tow behind trailer and keep your bed space for more cargo. Just an FYI....

Happy towing!

 

4x4 with electronic locking differential is a winner every time. These trucks are heavy, especially in the front end. In 2wd I have gotten stuck in wet grass {on an incline}with factory tires many times. I have even got stuck a few times using my locking diff. However when in combination of 4wd and locking diff, I make it out on every occasion.

I have pulled my TT through mud, sand, and grass with no problem with my F250.

 

Great explanation Greg, but I have one question, how does a locking diff from today compare to lets say a 70's style Dana 70 diff with posi traction? I know todays diff has more electronics but mechanically they act the same, am I correct?

 

"Posi" is just what they called it back then - it's still a locking differential as described above.

-Joe

 

Thanks Joe, todays terminology. Surprised they didn't put a hash tag in with it.

 

Limited Slip and Posi-Traction are two different terms for the same thing. They both have a clutch pack to try and keep the spider gears rotating at the same speed. The clutches work automatically with no driver input required. This type of system has been around for 50 years or more.

A true Locking Differential has some mechanical method to hold the spider gears so they do not rotate independently from each other. Some guys make a poor man's locking diff by welding the spider gears solid....makes for some chattering on hard surfaces but works fine for vehicles that spend 100% of the time off road. I presume the new Ford system is a true mechanical locking diff but I haven't inspected one to be sure. Normally a mechanical locking diff is pneumatic or electrically actuated. Dodge was the first manufacturer to offer a mechanical locking diff in a production pickup (big rigs have had them for quite some time). I presume it's so popular that Ford and Chevy have begun offering it as well. Prior to that, the only way to get a true locking diff in a pickup truck was via aftermarket.

 

Thanks for making me chuckle ---- hashtag is SO DUMB !!!!!!!!!!

I file it right under Polar vortex !

 

Shake N Bake answered the technical stuff perfect

My advice, go with 4x4 if you want "insurance" that you will be leaving, especially if in open field and wet grass.....

A 2wd with good tires and locker might be ok...but as mentioned....these trucks are nose heavy.

I would not be moving this trailer in 2wd in these conditions:

 

Thanks Greg for another great explanation.