Continued from Part 1, "A Word on 4WD"

The most confused issue regarding the transfer case is that "locking" it somehow affects the axles. This is only true of "shift-on-the-fly" 4WD systems, which we will get to later.

Locking your XCASE in 4WD has no affect on the differentials in the axles directly, or causes them to "lock".

Locking THE HUBS is NOT the same as locking the differentials (the center section/pumpkin). When you lock the hubs, you are allowing the two AXLE shafts to power the wheels.

Locking the DIFFERENTIAL is only accomplished by doing one of three things: Installing a locking center section which ALWAYS locks the differential (but allows racheting-read on), installing a "spool" /welding open differential, or installing a "lock-on-demand" unit like an ARB air locker. Unless you remember crawling underneath your truck and doing one of these things, I guarantee you that your axle differential does not lock.

Confused? Let's start back at the xcase to sort all of this out.

The possible positions on a part-time case are:
4H
2H
N
4L
2L (sometimes-but not on stock J trucks)

Most of the time, you will be driving in 2H meaning that only your rear axle is powered, and the xcase is in the equivalent of 4th gear in a manual tranny. (The highest gear) NOTE: if I wanted to really confuse you, I would discuss "Highest gear RATIO or highest GEAR", but mebbe that will be later� 2L is an option that came for one in the IH Scouts. It allows you to have low range without being in "4WD" so that you can pull for long distances on a dry surface among other things. Unless you convert your Dana 20 to a "twin stick" you do not have 2L.

4H drives both axles front and rear, and the xcase is again in the equivalent of 4th gear. 4L drives both axles also, but this time the xcase is in the manual equivalent of 1st gear, which means that since the xcase is in back of the tranny, every gear in the tranny is affected by either being much higher (H) or much lower (L).

H is for normal driving speeds. You wouldn't want to try to drive your truck 55 MPH in 4L-not unless of course you happened to order the special "MARLBORO-INDY" motor option with 15K RPM red line. L is used for low speed pulling/plowing, extra power for crawling home in deep snow, or engine braking on the decent of steep slopes (so you don't have to touch the brakes and slide).

Notice that I did not mention the wheels driving, just the axles. Even if you engage both axles by being in 4H or 4L, your front wheels can not drive unless you lock the hubs.

LOCKING THE HUBS enables the two axle shafts outboard of the differential to actually power the wheels. Unless they are locked, your axle shafts will be powered when in 4WD, but they will not power the wheels. (Of course the wheels will hopefully be spinning passively by virtue of being pushed by the rear wheels.)

Locking hubs exist because it seems to make sense that when you are NOT in 4WD, you don't need to be spinning the extra mass of the axle shafts, differential, and driveshaft (propeller shaft). If there were no hubs, the front driveshaft would spin all the time because the wheels would make the axle assembly spin thereby driving the driveshaft when in 2WD. I wonder how much this affect wear and MPG, though, because some early J trucks and a lot of Dodges do not have locking hubs at all. In those trucks the drivetrain spins up to the xcase all the time. You would think that if Dodge could squeeze an extra 1 MPG out of their trucks to get in good with Big Brother that they would have which makes one think that the difference is negligible. I'm also not aware of Dodge trucks wearing out their Dana 44 axles any faster than anybody else's rigs�

There is another kind of hub and that is the AUTO HUB. They are usually used with full-time cases and are supposed to be locked when under power and floating when (if) the front axle is not powered. However, with a QuadraTrac, this is never supposed to happen but it can if the "posi" differential IN THE XCASE is worn out. The NP203 style (for example) full-time cases found in the Big Three's trucks sometimes operate in a condition where EITHER the front OR the rear axle is powered because their xcase differentials function similarly to an "open" rear differential. See the QT section under the Tranny and Xcase section to get an explanation of how QTs work.

For now, just assume that every full-time system drives BOTH axles all the time for simplicity's sake until you've read the QT page.

FULL-TIME SYSTEMS THAT LOCK- here I think, is another area where folks get confused. I am going to speak in general terms, because I can't keep track of every combination of full-time system out there. Some full-time systems have a 4H full-time AND 4H LOCK position. The difference is that in 4H full-time the xcase is in 4WD, but allows some "slippage". In 4H LOCK, the differential that allows slippage normally is locked with a collar or a pin of some sort that takes away the differential action and splits the torque output 50/50 between the front and rear axles just like a part-time xcase in 4H with no provision for slippage or driving on a dry surface.

Coming soon- SHIFT ON THE FLY 4WD. A good idea that is hard to execute well, dependably.