Stock Tcase

[The Yeti]

Just curious without reading the book then googling and forum searching for days. I'm new to the Jeep world with my 21'Gladiator 80th anniversary. Fsr as I can tell it would be like a Sport S pretty much (maybe I'm wrong) I'm from the Chevy world specifically the Duramax world. The transfer case on this unit says 2wd 4wd auto then 4wd part time then low. An someone explain how this unit works exactly? I get auto, I assume it must kick in and out when something slips but then 4wd "part time"? Wtf thats new to me...

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[ShadowsPapa]

Just curious without reading the book then googling and forum searching for days. I'm new to the Jeep world with my 21'Gladiator 80th anniversary. Fsr as I can tell it would be like a Sport S pretty much (maybe I'm wrong) I'm from the Chevy world specifically the Duramax world. The transfer case on this unit says 2wd 4wd auto then 4wd part time then low. An someone explain how this unit works exactly? I get auto, I assume it must kick in and out when something slips but then 4wd "part time"? Wtf thats new to me...

4 wheel drive PART TIME is where the front and rear driveshafts are locked together in the transfer case. It does not allow for any speed difference at all between front and rear axles.
NEVER use this on a solid surface like concrete, blacktop and so on.
It's exactly like any other older pickup with a 4 wheel drive high option. You'll "wind up the drivetrain" and cause stresses and even make it hard to get back out into 2 wheel drive.

The 4 high auto is a system with clutch packs and it reads the relative speed of the 4 wheels and if it "sees" a slippage problem it engages the clutch packs inside the transfer case to transfer torque to the front driveshaft as needed.
It's a rather complex system.
You can run it on any surface - like a highway with some ice, then clear spots for a quarter mile, then ice and show, then clear again and not have to shift in and out of 4 wheel drive. You can leave it in that position in heavy rain, snow and ice.
4 high part time you would need to take it out of 4 wheel drive for driving on dry pavement between snow drifts.

My 2011 Silverado 4x4 had an "auto" mode for the dial on the transfer case - it was similar. You could drive it on any surface and it only engaged when it detected wheel slippage.

this is really nothing new at all - it's a system similar to that in other Jeeps like the Grand Cherokee and so on for years, similar to modern Chevy and Ford with an "auto" position for the transfer case.

When I say how it works is complex - it's sort of counter to what you'd expect. When sitting at a stop light in 4H auto, the clutch pack is actually engaged and with the right software, you can observe how it applies, what percentages of application and so on.
But again, it's not really different than what other vehicles have used - maybe how it shows you or the names it uses, but it closely matches the "auto" dial on a Chevy truck.

2 is exactly what is says - 2 wheel drive only. The FAD (Front axle disconnect) has split the right axle and there's no power going to the front driveshaft.
4H auto is 4 wheel drive - automatic mode. It senses wheel slippage and delivers torque to the front and/or rear driveshafts as needed via a clutch pack system.
4H part time is - use it on slipper surfaces only - not dry pavement, etc.
4L is 4 low, a low gear ratio for crawling slowly on tricky surfaces - like any other transfer case for the last several decades.

If it's got the 4 high auto, it's Selec-Trac

It's an option on Gladiators,
but it's standard equipment on Wrangler 4xe (4 by E) PHEV.
That's because those are high torque hybrids and the torque output is limited on those in 2 wheel drive but slip it into 4H auto and it no longer limits torque and is a real demon among Jeeps.

 

[The Yeti]

I see, so when winter hits, for city driving its 4wd auto (similar to a chevy half ton) in thia thing. Then 4wd part time for a mild trail at moderate to regular speed within reason and 4wd low for the low speed stuff as normal. The 3/4 ton and 1 ton chevys don't have auto (until 21' + I believe which changed the dmax city/towing winter city driving 4x4 game IMO) but I am familiar with the half ton Auto tcases too. 4Low is a rare necessity with those and if you need it you were probably looking for it. A jeep is a different bread built for a different purpose. Being that mine isnt a Rubicon I'm sure its not as purpose built but I can only assume should still function well enough. Thank you for the info and well said description. Gives me a better insight here to go from. I have a lot to learn here. Trying to avoid the modding bug on this thing but I've already started with a few minor things that add up fast. I really shouldn't have made this account haha. Appreciate the info though. Thank you

 

[LouisvEarlleJT]

For further info, the “part time” moniker is, I believe, a hold over from when vehicles could come equipped with full-time 4wd. A good example of that is 70’s chevy trucks which could come equipped with full-time 4wd, it was always locked in. Contrast that with a “part-time” of the same era which required the driver’s input to lock it in.

Here’s a fun magazine ad for it: https://www.xr793.com/wp-content/uploads/2017/07/1976-Chevrolet-4-Wheel-Drive.pdf

 

[ShadowsPapa]

For further info, the “part time” moniker is, I believe, a hold over from when vehicles could come equipped with full-time 4wd. A good example of that is 70’s chevy trucks which could come equipped with full-time 4wd, it was always locked in. Contrast that with a “part-time” of the same era which required the driver’s input to lock it in.

Here’s a fun magazine ad for it: https://www.xr793.com/wp-content/uploads/2017/07/1976-Chevrolet-4-Wheel-Drive.pdf

There were Jeeps and others using such transfer cases with differentials in them that allowed 4 wheel drive full time.
They had to differentiate between having the differential action between axles, or having the driveshafts locked.

I can tell you from experience that the full time 4 wheel drive of that era was pretty worthless in many cases. Get onto any snow pack, ice, or even wet grass and you could spin a wheel just as easily as 2 wheel drive.
Personal experience because AMC used these in the Eagle, 1980 through 1988 (and similar transfer cases in Jeep prior to that)

NP 119 - '80 thru early '81 -- Full Time 4 Wheel Drive; Viscous Coupling
NP 128 - 1986 only; Open Differential
NP 129 - mid '81 thru '88 -- Select Drive Models; Viscous Coupling

A 1986 Eagle was "ok" but you could also spin a wheel. Note that they tried that NP128 for only one model year and then went back to the viscous coupling 129.
If you have a front wheel on something slick, the torque can go mostly to the front driveshaft, through the carrier and spider gears to that spinning wheel, leaving the others with almost nothing.
It's better than 2 wheel drive, but it's something I'd not even consider having these days.
The 228 was just as bad as the 128 but at least had a low range - it was mid-80s Jeep. Eagle never had a low range of course.
The 242 had a full time high position but also had high lock (Part time 4H)

That PDF of the Chevy was the most common situation of the era.
They had to differentiate and anyone who had a 4x4 knew the difference - really need traction off the pavement, you moved it to 4H part time. If you really needed down low grunt, pulling power with all 4 wheels, it was 4L

Jeep, Ford, Chevy, it's just how it was.
Today isn't much different in nomenclature except that the full time 4H is automatic - it's not an open differential like decades ago - it can lock the driveshafts using clutches.
Same principal on non-slick surfaces, but when traction loss is detected, instead of that wheel spinning, the clutch pack is locked to various degrees to send more torque to the other wheels.

Selec-Trac -

When in 2wd, the clutch pack is relaxed.
In 4H part time, the clutch pack is fully locked
In 4H auto, when you are stopped or driving very slowly, it's locked, then as you increase speed, it relaxes and unlocked but there is a little pressure to be "on the ready" for wheel slippage.

4H auto - slow speed

4H part time -

4L it's locked -

 

[The Yeti]

Both awesome and informative reads. Nice little throwback article link there and super good info on the current set up.

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