Mike Romain

The shift on the fly feature works really well in both of our Jeeps. I
live in Canada and just treat 4 hi like any other shift. When I see
snow on the road I shift in, when it clears, I shift out. I also find 2
better at snow or slush covered intersection corners. I shift back to
4x4 as I straighten out.

Running in 2 high is usually best for mileage.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's

Sandstone wrote:
>
> I'm thinking about buying a Jeep Liberty. I know Selec-Trac may be a
> better option but all the Libertys I've looked at have Command-Trac.
> Selec-Trac just rarer than hen's teeth around here. Command-Trac might
> be OK but I'm worried about the 4Hi limitations.
>
> Does the problem with 4Hi on dry pavement only occur when turning?
>
> For the sake of argument, if you *only* drive in a straight line on dry
> pavement, no matter what the speed, then is there any 4HI problem?
>
> I'm concerned about driving on hard dirt or clay roads that have
> intermittent trouble areas (e.g., deep sand or mud spots). Do I dare
> drive in 4Hi on roads like this, or are they equivalent to dry pavement
> scenarios? What are others experiences in situations like this?
>
> What about gravel roads - are they problematic in 4Hi?
>
> TIA

L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III

It's in four wheel drive, just that the four inches of travel from
the independent front suspension is not enough to find traction from the
bottom of a six inch wash front and rear diagonally across the road.
Example: http://www.ohiomurals.com/jeepin/axles.htm
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Billy Ray wrote:
>
> What is with the delay in the front from kicking in?
>
> --
> .
> Billy_Ray@SPAM.fuse.net (remove SPAM)
> 2002 Jeep WJ 4 Liter Automatic
> Brilliant Black Crystal Pearl Coat
> Sharing is why we are all here....... or should be.

L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III

It's in four wheel drive, just that the four inches of travel from
the independent front suspension is not enough to find traction from the
bottom of a six inch wash front and rear diagonally across the road.
Example: http://www.ohiomurals.com/jeepin/axles.htm
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Billy Ray wrote:
>
> What is with the delay in the front from kicking in?
>
> --
> .
> Billy_Ray@SPAM.fuse.net (remove SPAM)
> 2002 Jeep WJ 4 Liter Automatic
> Brilliant Black Crystal Pearl Coat
> Sharing is why we are all here....... or should be.

L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III

It's in four wheel drive, just that the four inches of travel from
the independent front suspension is not enough to find traction from the
bottom of a six inch wash front and rear diagonally across the road.
Example: http://www.ohiomurals.com/jeepin/axles.htm
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Billy Ray wrote:
>
> What is with the delay in the front from kicking in?
>
> --
> .
> Billy_Ray@SPAM.fuse.net (remove SPAM)
> 2002 Jeep WJ 4 Liter Automatic
> Brilliant Black Crystal Pearl Coat
> Sharing is why we are all here....... or should be.

L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III

It's in four wheel drive, just that the four inches of travel from
the independent front suspension is not enough to find traction from the
bottom of a six inch wash front and rear diagonally across the road.
Example: http://www.ohiomurals.com/jeepin/axles.htm
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Billy Ray wrote:
>
> What is with the delay in the front from kicking in?
>
> --
> .
> Billy_Ray@SPAM.fuse.net (remove SPAM)
> 2002 Jeep WJ 4 Liter Automatic
> Brilliant Black Crystal Pearl Coat
> Sharing is why we are all here....... or should be.

L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III

Then you have two wheel drive.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Billy Ray wrote:
>
> My 02 WJ with Select-Trac does not have posi-traction.
>
> --
> .
> Billy_Ray@SPAM.fuse.net (remove SPAM)
> 2002 Jeep WJ 4 Liter Automatic
> Brilliant Black Crystal Pearl Coat
> Sharing is why we are all here....... or should be.

L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III

Then you have two wheel drive.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Billy Ray wrote:
>
> My 02 WJ with Select-Trac does not have posi-traction.
>
> --
> .
> Billy_Ray@SPAM.fuse.net (remove SPAM)
> 2002 Jeep WJ 4 Liter Automatic
> Brilliant Black Crystal Pearl Coat
> Sharing is why we are all here....... or should be.

L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III

Then you have two wheel drive.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Billy Ray wrote:
>
> My 02 WJ with Select-Trac does not have posi-traction.
>
> --
> .
> Billy_Ray@SPAM.fuse.net (remove SPAM)
> 2002 Jeep WJ 4 Liter Automatic
> Brilliant Black Crystal Pearl Coat
> Sharing is why we are all here....... or should be.

L.W.(=?iso-8859-1?Q?=DFill?=) Hughes III

Then you have two wheel drive.
God Bless America, ßill O|||||||O
mailto:-------------------- http://www.----------.com/

Billy Ray wrote:
>
> My 02 WJ with Select-Trac does not have posi-traction.
>
> --
> .
> Billy_Ray@SPAM.fuse.net (remove SPAM)
> 2002 Jeep WJ 4 Liter Automatic
> Brilliant Black Crystal Pearl Coat
> Sharing is why we are all here....... or should be.

Jerry Bransford

When your Selectrac is in the 4Hi or 4Lo position, that is a "part-time"
4x4 system so there is no delay in torque being sent to the front, the
torque is split equally between the front and rear.. Neither is there a
delay in power reaching your front axle when you're in the 4Full setting
since Selectrac uses a differential between the front and rear axles.
Delays in power reaching the front axle are commonly encountered in AWD
and some 4x4 systems that rely on electronics to engage the front axle
in RWD 4x4 vehicles. I wrote a FAQ for a Jeep forum I've copied below
that covers some 4x4 and torque-related questions that might help you
understand this frequently misunderstood subject a little better...

"All four wheels are pulling if all four wheels have equal traction. If
all four tires have equally good traction, then all four will pull
equally well.

A standard open differential always (always!) splits the torque 50:50
between both sides. The problem is that when one tire starts spinning
due to poor traction, that reduces the amount of torque seen by either
side by an exactly equal amount. So if one side starts slipping, the
other side's power (torque) is reduced by a corresponding amount which
usually means insufficient power to keep you moving. The axle can
deliver no more torque than the side with the least amount of traction
can take before slipping.

So the short answer is 'yes', all four pull in 4wd. But the moment one
side starts slipping, neither side gets enough power to keep you moving
even if the non-slipping side still has traction.

Why does the power (torque) get reduced to both sides and not just the
side that is slipping? Again, because the differential will always (!)
split whatever torque it sees 50:50 to both sides (few people know
that). Why does the amount of torque get reduced at all? Because the
engine only develops torque when it is working into a resistance. Run an
engine with a torque meter connected to it and watch what happens to the
amount of produced torque as resistance to the engine is varied. When
the engine is working into zero resistance and just running free, it
produces nearly zero torque. Apply a braking action to the engine and
the amount of torque will increase in direct proportion to the amount of
resistance it is seeing. The more braking force applied to the output
shaft, the more torque the engine produces.

So because the engine only produces torque when seeing resistance, a
spinning tire reduces the amount of power (torque) the engine produces
because the engine is only seeing the nearly zero amount of resistance
produced by the spinning tire. This works the same way with 2wd and 4wd,
it's just that with 4wd, you have more of a chance that at least one of
the two axles will have enough traction to allow the engine to produce
enough torque to keep you moving. Which is why you get stuck in the
first place... when one side is spinning, there is insufficent power
being delivered to the other side to get or keep you moving.

And all of this is why a limited slip differential (LSD) can help since
it helps to "couple" (via a clutch or a gear-based device) the
resistance the side with good traction is seeing to the other side with
poor traction, increasing the amount of resistance seen by the engine...
thereby increasing the amount of torque delivered to both sides. Which
is why the simple technique of stepping on the brakes a little when a
tire is spinning can often get you unstuck... because it too increases
the resistance the engine is working into which increases the amount of
torque that is delivered to the wheels. Or if a rear tire is spinning
constantly, pulling the parking brake on a couple clicks can often help
by acting as a poor-man's limited slip differential.

What does a locker do? It mechanically locks the left and right wheels
together so when one turns, they must both turn at the same speed. This
arrangement prevents one side from spinning uselessly while the other
side does nothing. Automatic lockers are always locked but they unlock
automatically to allow the outside wheel in a turn to 'ratchet' faster
as the outside tire must do through the turn. Once the turn is
completed, the locker re-locks both sides together. A manual locker is
one that doesn't lock the left and right sides together until it is
actuated either via a push-button or lever. An ARB Air Locker is
air-pressure actuated, others like the Detroit Electrac are electrically
actuated. The Ox Locker is actuated via a lever and cable. Manual
lockers have an advantage for on-road driving in that when unlocked,
they act like an "open" axle... i.e. one without a locker or limited
slip differential... which means it drives like an unlocked vehicle
until the locker is activated via the push-button or lever.

Part-Time and Full-Time 4x4 systems...

A part-time 4x4 system called Commandtrac which is in all Wranglers
together with low-end Cherokees and Libertys locks the front and rear
axles together inside the transfer case. Because they are locked
together, the front and rear tires must rotate at the exact same rpms.
However, the front tires must rotate faster than the rear tires during
any turn so a part-time system fights that... which makes a part-time
system inappropriate on a paved road because the high level of traction
on a paved road prevents the tires from slipping which would otherwise
allow the front and rear tires to grudgingly rotate at different rpms.
Offroad this is not a problem since the poor traction of an offroad
trail allows the tires to slip as needed. But when they try to
slip/rotate at different rpms on a high-traction surface, the entire
drivetrain is stressed which is bad for it. This problem is called
"wind-up".

Finally, a full-time 4x4 system like Selectrac is available on Grand
Cherokees, Cherokees and Libertys couples the front and rear axles
together, but they are not mechanically locked together like they are
with a part-time 4wd system. The front-to-rear axle coupling can be done
via either a differential like the Selectrac system uses (just just like
what is in the center of the axle) or a fluid (viscous) coupler. The
benefit to a full-time 4wd system is that because the front and rear
axles are not mechanically locked together, the front and rear
tires/axles can rotate at different rpms from each other. This allows a
vehicle with a full-time 4wd system to drive in 4wd "full time" on a
paved road without problem since there is no 'wind-up' problem to harm
the drivetrain. You cannot get a full-time 4x4 system in a Wrangler from
the factory."

Hope this helps!

Billy Ray wrote:
> What is with the delay in the front from kicking in?
>

--
Jerry Bransford
PP-ASEL N6TAY
See the Geezer Jeep at
http://members.***.net/jerrypb/