4wd Auto & 4wd Part Time

[DiscoDino]

Hi everyone - I'm new to the Jeep world with my JTR so unfamiliar with these two terms and what do they do mechanically...I've searched as best I can and didn't find anything solid on the subject...with Land Rovers and G-Wagons...it was always 3 open diffs 4wd, and then engaging the 3 diffs we locked ...so what's the difference between Auto and Part Time?

Thanks!
Nadim

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[scuuuud]

https://www.jeepgladiatorforum.com/forum/threads/newbie-question-4wd-auto-part-time.24254/

 

[DiscoDino]

https://www.jeepgladiatorforum.com/forum/threads/newbie-question-4wd-auto-part-time.24254/

awesome, thanks!

 

[ACAD_Cowboy]

The quick and dirty answer:

Part time 4wd:
Transfer case disengaged = power to rear axle only, limited slip or locking differential in axle
Transfer case engaged = power to front and rear axles, 50/50 fixed split, limited slip or locking differentials in axles
High and Low range if equiped

Full time 4wd:
4wd auto = transfer case acts as a limited slip differential, applies variable power to axles based on conditions, axles as above
4wd lock = transfer case acts as "normal" transfer case, 50/50 power split, axles as above

Full time 4wd allows the front and rear axles to speed up and slow down relative to each other in addition to allowing the left and right wheels to do the same. For you the driver it allows you to have seamless transitions in slippery conditions when used with vcs and abs. But... it is not "as capable" when used in offroad conditions. Most people driving most vehicles don't do what we do and these systems are just fine. At the other end of the spectrum is a traditional differential in low range with locked axles which provides maximum tractive effort with the minimum of steering control.

The main purpose for part versus fill time is the control drive shaft forces. If you drive your part time system engaged on pavement the grip of the tires on the pavement will cause rotational tension to build up in the drive shafts like a twisted rubberband. It will cause, at the good end, power train twist which makes shifting gears and ranges a chore and at the bad end, broken parts. If the surface is wet, muddy, dusty, snowy, sandy or otherwise loose then the wheels can slip enough to control this.

A part time system requires you the driver to disengage it as needed.

A full time system uses the differential action in the transfer case to control these forces and as the systems got more mature they can also disengage the front or rear completely with variable and dynamic control which is what lets all these nifty awd sports cars do what they do. But they suck wind offroad.

If softroading and assured poor weather driving is goal a full time system like jeep offers in select-trac 3 is a great option. If you plan on getting out in it then command-trac is for you and likewise if you like playing stupid jeep games to win stupid jeep prizes, rock-trac is the key to scratches, dents and stressed out leaning over.

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