Limited Slip in 4x4 vs. 4x2 ???

Hi - I've never owned a truck or 4x4 before.  I want to buy a 2008 F350 Diesel SRW Crew Cab Short Bed for a future 5th wheel (the truck will be sufficient for the 5er I have in mind).  I've been obsessing about whether to get a 4x2 or 4x4.  I will likely be a "fair weather camper".  However, I may use the truck as my "daily driver".  Although we don't get too much snow in southwest Indiana (right on Kentucky border), this brings me to several questions regarding the 4x2 versus 4x4 configuration with a limited slip rear differential:

1)  Although I may have misunderstood something, I read on RV.net that only one wheel (not two) really is powered on a 4x2, whereas only two wheels (not four) really are powered on a 4x4.  Is this true, and does this apply with or without limited slip?  As I mentioned, I may have misunderstood something.

2)  Is limited slip beneficial on BOTH 4x2's and 4x4's?  I don't really understand how that feature works other than it is "smart" enough to power the wheel with the best available traction.

3)  On a slippery road (but without any snow on it), I heard that 4x2 diesels are VERY front heavy (due to the heavy engine) and, thus, must be weighted down in the rear to be safe to drive with.  Is this true and does this also apply also to 4x4 diesels?  As I understand, 4x4's have more weight in the rear due to the transfer case, but I wasn't sure if that means I don't need to weight down a 4x4 in the rear also while traveling on slippery roads. 

In other words, I'm trying to understand how much disadvantage I will have with a 4x2 versus 4x4 while traveling on slippery (but not snow covered) roads.  I'd like to get a 4x2 since I'll likely be a "fair weather camper" and hear they get better mileage, ride better, sit lower and cost less to buy/maintain.  However, since it will be a daily driver, I want to make sure that I won't be totally paralyzed in icy conditions which we usually only get once or twice per year.

Thanks!
Gary

I'd personally go for the 4x4. One of the nicest things I found with our 4x4, when towing, was the ability to maneuver the 5th wheel in tight conditions. You just put the transfer case in low range and then you have the power to do everything at an idle. It also helps when you have parked on grass and there is a big storm the night before you want to leave--had this happen to me more than once.

Old farmer's saying. "You can always send a man to the field to do a boy's job, but you can't send a boy to do a man's job."

Take a hard look at the Dodge diesel. They consistently get better mileage than the Fords.

Chet18013

We had a F250 4x2 limited slip for awhile. A couple of times we wished we had the 4x4 instead, cause we got stuck twice: once on wet grass (!) on a campsite after a heavy rain and once in loose gravel on a campground hillside road. Got down in a gully and couldn't climb out cause the gravel they had poured in to fill a mudhole just spun out from under us. Another camper hooked on a tow strap each time to give us an assist and we were out in less than an hour each time.  You may never encounter such a situation. I am pretty aggressive about getting my rigs into campsites I like, even if small, rough or at the end of a bad road. Even camped on a gravel river bottom in Alaska once and also in an abandoned quarry.

As for what you heard, ANY pickup truck is light in the back when empty - it's the nature of the beast. A diesel, with the heavier engine, may be more so, but there is no need to weigh down the rear end for daily use. It may ride a bit more comfortably with some weight in the back, though.  In winter snow, people often add weight to the back of a pick-up to improve traction.

The transfer case on a 4x4 is in the middle or front, so its weight doesn't help the rear end to any notable degree.

Yes, only one wheel on an axle is powered in an on-road vehicle (off road vehicles with locking differentials are a whole other story, not relevant here). That means a 4x2 is actually applying power to only one wheel. Limited slip transfers power to the other wheel if the primary one slips.  A 4x4 allows you to power two axles instead of one, but power is still applied to only one wheel on each axle. Since you do not and cannot normally drive on dry pavement with 4WD engaged, you are still running a 4x4 with only one wheel driving in most cases. But if you get in a slippery situation, there is no question the 4x4 is superior to a 4x2 Limited Slip.  The downside is that the 4x4 is heavier and slightly less fuel efficient.

RV Roamer said:

Limited slip transfers power to the other wheel if the primary one slips. 

Click to expand...

That's not how I understood limited slip works in most OEM LSD, that sounds more like the description of traction control where if one wheel spins, brakes will be applied to that wheel forcing power to the other one.

The type on my Nissan is a clutch type, power is sent to both wheels until the resistance on one side is greater then what the clutch can hold and the wheel with the most traction will slip causing the other to spin.  So when I get equal traction from both rear wheels, like on ice or mud, power is sent to both wheels.  But if one wheel is on a slippery surface while the other is on a hard surface, the one on the slippery surface will spin.  Same thing happens if on uneven terrain where one of the rear wheels does not have enough weight on it to provide traction, only that one will turn.

They are not built equal, so one manufacturer can have an LSD that remains locked most of the time while others will unlock at the slightest variance in traction.

Regardless how they work though, it's like you said, regardless of the LSD, is no replacement for 4x4, but it's a nice addition to a 4x2 or 4x4.

It's possible to help the LSD a bit with the use of the brakes.  If traction is uneven and a wheel slips, applying the e-brake just enough to cause some friction will cause the resitance to be closer to even on both sides and you may able to get power to both wheels.  Or with an 4x4 with LSD front and rear, you can use the brake pedal.

You would definitely do better with a 4X4.  I've been stuck on a hill...all dry, just had a bit of an incline to it and the tires just wouldn't grab.  My Dad has used his more times than he ever thought he would just maneuvering his 5er in and out of places.  If you can, get the 4X4.  You won't regret it.

Aside from all the advantages provided when towing with 4x4 just think of the fun you can have when you attend the Moab rally or the QZ rally and go off roading with your 4wd truck.

Sorry to revive an old post, but I wanted to share the weekend experience where 4x4 came in handy.  We went boondocking and had to drive roughly 8 miles on logging roads.  The first steep hill I got to, the rear tires slipped a few times because of a few loose pebbles I rolled on to.  Not a fun feeling when towing uphill, I switched to 4x4 and made it up with not one wheel spinning.

I the way out, it was even better, I used low range.  Because of the road conditions, I could not drive faster than 20 MPH anyways so low range was fine.  On the steep inclines, I could not really tell that the trailer was behind and going down the steep hills I dropped it in 1st gear, so I had plenty of engine braking, hardly used the brakes.

I think I will always use low range from now on when driving on hilly dirt roads.

Gary is right on his assessment of Limited Slip.  that/s exactly how it functions.

Better plan on attending Moab 2008 rally.  You will love the 4X4 trails there and you won't need to take your trailer out on the trails.

I would love to go to Moab, except it's close to 3000 miles from where I live and my vacations are too short.  Plus I would not drive that far with a trailer.  The Xterra is not geared well for highway driving.  I usually drive between 90 to 100Km/h (55 to 62 MPH) with the trailer, slightly faster without.  Any steep hill and I have to let it gradually slow down to 70 Km/h (43 MPH) at which speed I can manually downshift it to 2nd gear.  Then I can maintain that 70Km/h easily uphill, I could slowly accelerate if I wanted to waste fuel, but what's the point.

So for me, a trip to Moab would mean going by plane.

Maybe some day.  Beutifull country around Moab.