Jeep / Dodge 4WD system question

[Johnny248]

Can someone explain how these 4WD systems work?

Command Trac part time 4wd - front axle is always engaged and front drive shaft spins. Does this mean the Transfer Case does all of the switching? - This seems like it has a lot of drag or wasted energy while in 2WD?

4wd with full time - front axle has an differential lock actuator that locks front axle. Drive shaft does not spin. So the Transfer case engages as well as the front axle lock all together at the same time? Seems like the ideal system with 2WD,4L,4H, 4 Auto

 

[Invisible]

It's either a transfer case bolted to the transmission that has a planetary differential, which makes the vehicle AWD, or it's a transfer case that uses a wet clutch to engage the driveshaft for the front differential, which makes the vehicle 4WD. The ones with the clutch tend to be more expensive, and some have more complex computers and sensors than others, giving you multiple drive modes, etc. And some even have low range. That's about it, very simple.

 

[Kira]

Can someone explain how these 4WD systems work?

Drawings, diagrams and pictures have been a basic way to depict mechanical actions.
Therefore, I respectfully suggest you Google these systems.
Are you involved with a vehicle with Command Trac? If so, what year, model and engine?

 

[97prizm]

Can someone explain how these 4WD systems work?

Command Trac part time 4wd - front axle is always engaged and front drive shaft spins. Does this mean the Transfer Case does all of the switching? - This seems like it has a lot of drag or wasted energy while in 2WD?

4wd with full time - front axle has an differential lock actuator that locks front axle. Drive shaft does not spin. So the Transfer case engages as well as the front axle lock all together at the same time? Seems like the ideal system with 2WD,4L,4H, 4 Auto

There is a good YouTube video about the different systems that Jeep uses. Supposedly the select-trac is 4wd but part time with a center differential making it act like awd. The command track I think is what the wrangler uses ie 4wd and locked.

 

[meep]

I’d think that pretty much anything that is full-time 4WD or AWD will have all components spinning at all times, only varying clutch engagement. If any parts aren’t spinning, there’d be delay and ruckus to bang them up to speed the moment they are needed. Most of these full time systems don’t have front hubs to physically disconnect portions of the driveline.

 

[D60]

Honestly front lockouts and later CADs (central axle disconnects) have vexed manufacturers and continue to do so, even -- and perhaps especially -- Jeep.

The '87-95 YJs used a CAD, as did the XJ. Then with the TJ circa '97 they deleted it all the way thru the JKs ending 2018 (yes, there were 2018 JKs, sold alongside the new JL). Then the JL got a CAD but I hear they've at least deleted it on the Rubi Recon and 392 models.

Ford tried to retain manual lockouts on the SuperDutys and also have vacuum activation if unlocked. Honestly, I think the system is a nightmare.

Bubble body F150s ('97-03) used a vacuum actuated shift fork that's pretty good, but just like any shift fork can wear the pads and eat the fork.

1/2 ton F150s starting in '04 got IWEs (integrated wheel ends = engineer speak) and that's basically one vacuum hub at each wheel. These have been good for me but some have lots of problems.

I also think Chrysler's vacuum actuated CAD is surprisingly reliable, but some people hate it.

GM's electric disco in their IFS seems very reliable, but the earlier thermal ones were despised.

But yeah, it's not the end of the world to have all that stuff spinning. I prefer old school lockouts and typically lock 'em in Nov and leave 'em 'til March or April.

Sure, there is some sort of mileage penalty.

Finally, with all these systems there's a very short but steep learning curve. Many complaints are simply people too impatient or too stupid to spend 10 minutes reading a write-up. Once you understand how, say, Chrysler's vacuum system works, it's stupid easy to diagnose and fix. That said, electric shift t-cases add another level (oh my gaw, it's just soooooo tiring to pull that ugly lever on the floor!!!!)

 

[D60]

Also consider that for things like AWD cute-utes -- many of which are front biased -- everything spins all the time. There's no mechanism to disco the rear half shafts from the wheels.

 

[GMBoy]

Then there is my 78 CJ7 where the axle and hubs are free wheeling when unlocked by the warn hubs

 

[SC Maintenance]

Command Track is the simplest 4WD system. The 4wd engagement comes in the form of locking the front and rear wheels via the transfer case. Everything spins - whether in 4wd or 2wd - only difference in 4wd if the front is locked and under power. If not locked, it still spins, just isn't connected - so your axles and diff are always turning. Video below of the NP208 - which is a really common transfer case. Both my Nissan's work this same way. You loose about 1mpg vs a 2wd system.

The other type I am not 100% sure what your referring to. Other systems sometimes had locking hubs and the transfer case. In the old days the hubs were manual - and pretty trouble free except you had to get out to lock them. Then varios manufacturers went to auto locking hubs, and everyone's seemed to have problems. In the end, they figured out you really weren't saving that much gas - the only thing your not spinning is basically the front diff. Does anyone use locking hubs anymore?

 

[D60]

The NP208 is a part-time t-case with no "auto" function or clutches. But yeah, whether the stuff up front spins as an idler will be dependent upon the presence of locking hubs or a CAD.

Also, I didn't address the OP's question head-on because Jeep's nomenclature (ie fancy marketing speak) drives me crazy. At times I've really had to dig into their explanations and read between the lines to understand if it's just old-school, part-time driver selectable 4wd, AWD aka full-time 4wd, or AWD with a "center diff" lock.
That's all I need to know but Jeep can't bring themselves to say anything simply.

THEN you sometimes get names for systems that have low range as an option, like the KL Cherokees that could be ordered either way.

The point is you wind up trying to memorize proper names (SelecTrac) for otherwise common terms, and I just kinda gave up. They'll change 'em in a few years anyway

 

[meep]

Honestly front lockouts and later CADs (central axle disconnects) have vexed manufacturers and continue to do so, even -- and perhaps especially -- Jeep.

The '87-95 YJs used a CAD, as did the XJ. Then with the TJ circa '97 they deleted it all the way thru the JKs ending 2018 (yes, there were 2018 JKs, sold alongside the new JL). Then the JL got a CAD but I hear they've at least deleted it on the Rubi Recon and 392 models.

Ford tried to retain manual lockouts on the SuperDutys and also have vacuum activation if unlocked. Honestly, I think the system is a nightmare.

Bubble body F150s ('97-03) used a vacuum actuated shift fork that's pretty good, but just like any shift fork can wear the pads and eat the fork.

1/2 ton F150s starting in '04 got IWEs (integrated wheel ends = engineer speak) and that's basically one vacuum hub at each wheel. These have been good for me but some have lots of problems.

I also think Chrysler's vacuum actuated CAD is surprisingly reliable, but some people hate it.

GM's electric disco in their IFS seems very reliable, but the earlier thermal ones were despised.

But yeah, it's not the end of the world to have all that stuff spinning. I prefer old school lockouts and typically lock 'em in Nov and leave 'em 'til March or April.

Sure, there is some sort of mileage penalty.

Finally, with all these systems there's a very short but steep learning curve. Many complaints are simply people too impatient or too stupid to spend 10 minutes reading a write-up. Once you understand how, say, Chrysler's vacuum system works, it's stupid easy to diagnose and fix. That said, electric shift t-cases add another level (oh my gaw, it's just soooooo tiring to pull that ugly lever on the floor!!!!)

Wonderful write up. My f150 has the vacuum hubs and they haven’t given me any trouble, but I’m cautiously aware of that extra soft rubber pipe snaked through the A-arms.

 

[Skippy722]

The NP208 is a part-time t-case with no "auto" function or clutches. But yeah, whether the stuff up front spins as an idler will be dependent upon the presence of locking hubs or a CAD.

Also, I didn't address the OP's question head-on because Jeep's nomenclature (ie fancy marketing speak) drives me crazy. At times I've really had to dig into their explanations and read between the lines to understand if it's just old-school, part-time driver selectable 4wd, AWD aka full-time 4wd, or AWD with a "center diff" lock.
That's all I need to know but Jeep can't bring themselves to say anything simply.

THEN you sometimes get names for systems that have low range as an option, like the KL Cherokees that could be ordered either way.

The point is you wind up trying to memorize proper names (SelecTrac) for otherwise common terms, and I just kinda gave up. They'll change 'em in a few years anyway

It also doesn’t help they don’t really easily tell you exactly which system you got either. The Durango and WK2 twins were awful about this, and the Durango didn’t even label them! All V6 Durango’s have “quadra-trac I” aka 50/50 split and no low or locking range.

All 5.7’s until 2021’ish were “Quadra-trac II” that had a locking low range in addition to regular AWD. And now we have 3, because the SRT’s and R/T Tow n Go (not to be confused with the regular R/T) which is basically a beefed up Quadra trac I transfer case with user selectable torque splits.