Explanation of the Command trac and select trac

1quick1

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I couldn't really find too great of an answer so I figured it might be a good topic in the FAQ if someone could explain the difference between the two.
 

-=JoN=-

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Command Trac = Basic 4x4 system, offers the following:
4-Hi = all 4 wheels move at the same speed, only ideal for slippery conditions.

4-Lo = all 4 wheels move at the same time, but offers more torque at lower rpm's (i forgot the ratio) great when ur stuck, or when 4-Hi just doesnt cut it

2-Hi = where it's spose to be all the time, just both rear wheels are engaged

now Selec Trac has all of the above plus;

4-Full Time = another name for all wheel drive. you can have this engaged anytime, as it allows all 4 wheels to move at different speeds (unlike 4-Hi, where you will get binding, when you have engaged on dry/grippy surfaces)
this is ideal for the likes light rain, curvy roads...etc....

hope tis helps...(anyoen else add on or what not...) i didnt get too technical on it, maybe someone else might...

the jeep website actually has cool flash animation explaining it's different 4x4 systems
 

Marlon_JB2

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The gear ratio for Low Range is 2.72:1.

Also, the power split for SelecTrac Full Time is 48% to the front, 52% to the back.
 

grogiefrog

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I like to use Selec-Trac when raining and on county maintained dirt roads.
 

dnm45227

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so should i ask my wife not to use the 4hi on the commandtrac unless it's snowy or really raining cats and dogs, or would it be ok to use unless she gets some binding?
 

waldn

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Do not use 4 Hi on non slippery surfaces

Explanation from Jeep web site:

COMMAND-TRAC™
The Command-Trac™ transfer case is the heart of the Command-Trac™ part-time 4WD system. When engaged, both front and rear driveshafts are locked by a chain and gearset, which always turn at the same speed, forming a single drive unit. This is a rigid connection that does not allow for any differential action between front and rear driveshafts. Normal front-to-rear differences in the turning radii of the wheels (when cornering) are compensated for only through wheel slippage on driving surfaces. This transfer case allows for 2WD, 4WD High-Range and Low-Range as well as Neutral.

2 HIGH:
• Front axle spins freely
• Power sent to rear wheel
4 HIGH:
• Shift-on-the-Fly at speeds up to 88 km/h (55 mph)
• Front and rear drive shafts lock together and rotate at the same speed
• Only use on slippery or loose surfaces
NEUTRAL:
• Use for towing your Jeep ® vehicle behind another vehicle
• Does not require uncoupling driveshafts
4 LO:
• Use for severe off-road situations
• Increases available engine torque by 2.72:1
• Slow speed to 3-5 km/h (2-3 mph), put transmission in Neutral
• Engage 4 LO and return transmission to desired gear

SELEC-TRAC™
The Selec-Trac™ transfer case is the heart of the Selec-Trac™ 4WD system. The difference is its Open-Centre Differential. In the 4 part-time position, this differential is locked and the system operates the same as Command-Trac™. In the 4 full-time position, the centre differential is open and allows the front and rear axles to rotate at different speeds when turning corners on high-traction surfaces or while driving over any kind of road surface. The Selec-Trac™ transfer case delivers the added convenience of not having to shift back-and-forth between 2WD and 4WD.

2 WHEEL DRIVE:
• Front axle spins freely
• Power sent to rear wheels
4 PART TIME:
• High-range, for temporary conditions that require extra traction
• Locks centre differential; all four wheels rotate in unison
• Not to be used on dry pavement
4 FULL TIME:
• High-range, for year-round traction, wet or dry
• Centre differential allows the front and rear axle to rotate at different speeds
NEUTRAL:
• Use for towing your Jeep® vehicle behind another vehicle
• Does not require uncoupling driveshafts
4LO:
• Use for severe off-road situations
• Increases available engine torque by 2.72:1
• Slow speed to 3-5 km/h (2-3 mph), put transmission in Neutral
• Engage 4 LO and return transmission to desired gear
 

dnm45227

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thanks for the info. i just want to make sure i get it straight before i relay it to her. are wet roads considered slippery enough, or does it strictly have to be sand, snow, mud?
 

Tightwadsjeeper

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dnm45227 said:
thanks for the info. i just want to make sure i get it straight before i relay it to her. are wet roads considered slippery enough, or does it strictly have to be sand, snow, mud?

I don't know what the manual says, but IMO, wet pavement (concrete, ashpalt, etc.) is NOT slippery enough to engage the 4WD (Command-Trac, etc. part-time 4WD). Think of it this way... if you're not WORRIED about getting stuck or just spinning your tires, you don't want to engage the 4WD.

Luis
 

grogiefrog

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Tightwadsjeeper said:
dnm45227 said:
thanks for the info. i just want to make sure i get it straight before i relay it to her. are wet roads considered slippery enough, or does it strictly have to be sand, snow, mud?

I don't know what the manual says, but IMO, wet pavement (concrete, ashpalt, etc.) is NOT slippery enough to engage the 4WD (Command-Trac, etc. part-time 4WD). Think of it this way... if you're not WORRIED about getting stuck or just spinning your tires, you don't want to engage the 4WD.

Luis

Agree. Now buckets of water, sure, why not!

That is the advantage of selec-trac, as you can use it for mixed conditions.
 

AtlanticLiberty

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Other than costs, why would Jeep even build anything other than Select-Trac? Is there a down side to it? You'd think it would be most cost-effective to put Select-Trac in all the Libs and be done with it. That way they wouldn't have to produce both of these...
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maureen58

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The first thing to consider for DC is the cost factor. That's why you have 4 cylinder base engines, manual trans, maybe no a/c, no radio, etc. Now if you look into it closer, select-trac is a great system, the number 1 option I look for. I live in Minnesota and we are suseptable to ice and snow. I can put into full time and have that added security whenever I want. But if you are a ********* off-roader there are problems having it. Even though they say full time gives you a 52 - 48 torque split front to rear, it is still an open type differential. You cannot attain the same total traction and control achieved with the part-time mode otherwise select-trac wouldn't need the part-time position with it's 50-50 locking split. Now if you are especially into rock crawling you can't or don't want to use full time because of the possible slippage so you use the part-time. But in flat, dry turning situations you need to shift into 2 wheel so not to bind your system. So you end up constantly shifting back and forth from 2 hi to 4 hi down to 4 lo for going vertical. Look at the above picture for the shift pattern of the select-trac and you can see what you would be shifting into. No mistakes, just a thought. Pay the extra and get the select-trac. In most situations off road it doe a respectable job. On a similar thought, why not make trac-lok standard. It has a similar cost to select-trac. Again we have a cost factor. Also there are people who don't want and or need it. I had it on a rear drive car and I could go places as well or even better than some front drive cars The down side was on ice you lose lateral stability. So in an icy state like mine, trac-lok may not be desired whereas if you spend any time off-road, it's a very necessary option. Most people will not drive their Jeep off-road, hence most people don't need it.
 

Se7enLC

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If you have the option for 4-fulltime, use that for rain / wet roads instead of 4-parttime. Even light snow should be good for 4 fulltime. 4-fulltime powers the 4 wheels, but doesn't have the driveline binding problem with turning sharply.

If you don't have 4-fulltime, however, I see no reason not to use 4 parttime in the rain. I got a 4wd vehicle so that in bad weather, I could use 4wd. So long as you are going in a straight line, even dry pavement isn't bad for 4wd, it's the corners where the wheels want to go different speeds but can't because they are locked together.

I use 4-PT on the highway/normal roads in the rain/snow, but switch to 2wd when I am pulling into a parking spot / driveway. I'd much rather deal with a little bit of driveline binding than lose traction on the highway in the rain. You'll notice when you're being bad to it....when you turn sharply in 4PT, it feels like the ebrake is on, and you need to give it a lot of gas to get it to go. Also, the tires skip and making a chirping sound if the pavement is dry. It'll be obvious that it's not a Good Idea.

As for advice to give to the spouse if they don't know which to use, it's 2Hi all the time, and 4FT when the weather gets bad. 4PT and 4Lo are for special cases (like, a few inches of snow on the road or driving through a snowbank or something).
 

Derek Mc

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As the Jeep wil be driven almost exclusively by my wife and as we get a whole heap of bad weather and (finally) as it is an auto CRD and has Selec-trac it will run in 4 Full-Time during the wet Scottish winter months when I drive I will run 2WD unless it's terrible, that seems to be te logical to my safety angel where we transport our baby daughter in the rear.
 

UKKJ

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Derek,

If the Jeep is fitted with Trac Lock, my experience with our greasy wet roads means putting it into Full Time 4WD at the first signs of rain...

...It is the V6 and power delivery is different, but with the LSD and the smallest amount of throttle on roundabouts sees the thing steps sideways..

....It is a controllable slide, but it scares the wife and other drivers when it happens!!!..I have also exited the works car park sideways, which is a bit dodgy when the bosses car is millimetres away!!

Just a recommendation...have fun
 

Derek Mc

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OK I see what your saying so RWD for me 4wd for her, uncontrollable grins all round for different reasons then \:D/
 

Stankleberry

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Does anyone know how much more gas 4WD uses than 2WD? I assume 4 Full time and part time use the same.
 
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