All wheels locked

okay not one word what the tires of the car are rolling on
dirt or ice. or raw hard pavement
nor the exact control settings are set.

the jeeps have many 4wd options new, (I have 2020 here)and I have full factory service manuals on all GC. made. gen 1,2,3.
most have Three levels of 4WD.
2005 to 2010 same as mine.
came with 2 choices new of transfer cases not told by you at all.
lets do both and answer what THEY DO and DO NOT DO.
nv140
The NV140 Quadra-Trac I (no part time modes) and uses brakes top stop tire slip. (smart)
is a single-speed transfer case and it is used in the Quadra- Trac I Full-Time 4-Wheel Drive System. It
provides full-time 4-wheel drive. The transfer case operates with an open center differential dividing engine torque
nearly evenly with 48 percent of engine torque to the front axle and 52 percent of engine torque to the rear axle. SO NOT YOURS

yours is this, read the users guide on 4wd low limits.
nv 245 has ,Quadra-TracT II and Quadra-DriveT II systems.
4wd low and lockups up the center differential.
and is not for pavement. (lacking ICE covering)
4WD Low, which multiplies engine torque 2.72
times and locks the clutch pack for maximum traction at all times
key word LOCKS. this for offroad and or ice only.
not for pavement.
do not use Low. or any kind of part time 4 wd modes, on pavement free if ice. (no matter the car owned)
or you windup the axles and steering fights the driver.
and is very dangerous to do and makes ABS go nuts. etc.
read page 240 in your users guide.
240
The Quadra-Trac IItransfer
case provides three mode positions - four wheel drive
high range, neutral, and four wheel drive low range.
and
The 4 LOW position is intended for loose, slippery
road surfaces only. Driving in the 4 LOW position on dry
hard surfaced roads may cause increased tire wear and
damage to driveline components.>. bingo the D word,.


if stuck in 4low
move one or more tire to ice or dirt.
shift out of 4low to 4hi at dead crawl speed,the slower the better
not grinding teeth to deathh wins.

4low is for dirt
or stuck in a snow drift.
otherwise stay out of 4low

https://www.carmanual.org/jeep-owners-manuals/2005-jeep-grand-cherokee-owners-manual-2983/

WJ jeeps.
what mode? 4h, 2l lock >?
why not just drive it and get it all loose and happy first.
get the gearlube hot, see if it wakes up, i bet it does.
there is no vacuum hose. that is part time. used long ago.
vacuum ended in 1995 with command trac.
the newer cars the front axle is cut out, inside the transfer case front end. ending vacuum and now electric.

Select track (stay off dry pavement in 4wd)
Quadra-Trac-II NV 247 Gerodisc system 1999+
Quadra-Drive NV247
if quada stay out of low or lock.

read this page,. and discover what you have.
or go under car, see that transfer case, see that silver and red tag
that is the NV number. what is yours>?
we can not guess options. ever.

http://en.wikipedia.org/wiki/Jeep_four-wheel-drive_systems

which one of 4.
http://www.wjjeeps.com/tcases.htm

are you on dirt? or pavement...????????????????????????
we cant answer until you answer what 4wd option you have.
if that makes no sense, then read the operators guide,
it tells you what's there and how to use it.
read that first, then ask questions,?
and if Part time 4wd?, it';s not to be used on dry pavement only ICE.

eg:

4WD: Select-Trac (or older Select-Drive has a slip coupling too, NP129/229) is AWD in that, "the "4Hi" setting the drive shafts were coupled together using a viscous-type coupler " this anti wind up slipper"
Watch out for exception 1: Select-Trac NP228 based jeeps, it does not have a viscous-type limited-slip coupling. It was used briefly in 1986.
Quada-Trac is full time 4WD (not in lock mode) has a real center differential to shift torque between front and rear. This is the best system , not just a slip clutch as above. Then went BACK to the slipper in 1980. (odd huh?) Up to 1998.
Quadra-Trac-II "4-All Time", "N" or neutral, and "4-Lo". In "4-All Time", torque is applied to the rear wheels under normal driving conditions.
If the rear axle starts rotating at a significantly higher rate than the front axle, hydraulic pressure builds up in the gerotor oil pump and causes the clutch pack, to progressively transfer torque to the front axle, until both axles return to the same speed
Quadra-Trac I was introduced in 2004-10, same as above but is automatic with no driver controls ,like above.
The Quadra-Drive system was introduced in 1999 and is based on the Quadra-Trac II system but adds limited slip differentials (the best full time system ,with great traction to all wheels all the time) 1999 to 04.
Quadra-Drive-II has electronic limited slip differentials or ELSDs 2005 up.

which system?
we cant guess what is In YOUR CAR, ever.
you must SAY. or RTM, in the glove box.
and why are you using 4wd on dry pavement, now>?


4WD: Select-Trac (or older Select-Drive has a slip coupling too, NP129/229) is AWD in that, "the "4Hi" setting the drive shafts were coupled together using a viscous-type coupler " this anti wind up slipper"
Watch out for exception 1: Select-Trac NP228 based jeeps, it does not have a viscous-type limited-slip coupling. It was used briefly in 1986.
Quada-Trac is full time 4WD (not in lock mode) has a real center differential to shift torque between front and rear. This is the best system , not just a slip clutch as above. Then went BACK to the slipper in 1980. (odd huh?) Up to 1998.
Quadra-Trac-II "4-All Time", "N" or neutral, and "4-Lo". In "4-All Time", torque is applied to the rear wheels under normal driving conditions.
If the rear axle starts rotating at a significantly higher rate than the front axle, hydraulic pressure builds up in the gerotor oil pump and causes the clutch pack, to progressively transfer torque to the front axle, until both axles return to the same speed
Quadra-Trac I was introduced in 2004-10, same as above but is automatic with no driver controls ,like above.
The Quadra-Drive system was introduced in 1999 and is based on the Quadra-Trac II system but adds limited slip differentials (the best full time system ,with great traction to all wheels all the time) 1999 to 04.
Quadra-Drive-II has electronic limited slip differentials or ELSDs 2005 up.

You need to be more specific. To start, which 4 wheel drive system your jeep has? (Select Trac, Quadra Trac II or Quadra Drive)
Then: does it never work, or only in 4-Lo?

a bad wheel speed sensor or not matching tires

Could you tell me what selection you have on your 4x4 shifter?

You have 4 high (full time) N 4 Low and nothing else?

Quadra only sends power to the front axle when it is needed, it uses a hydraulic unit that senses slip then send power to the front.

You also need to make sure your getting it in to gear right, for me I found that getting to 4 low can be hard as they tend to bind, move the 4x4 shifter to N take your foot off the brake and pull it into 4 low, do the same getting back out.

I have owned every 4x4 Jeep T case in Grands from 93 to 02 they offer fantastic traction and options and are strong.

Make sure your T case fluid is full, if you have never changed it DO SO, as dirty fluid plays hell on them, if you do have Quadra trac you need to get the correct fluid for the case, go to your Jeep dealer and get it, DONT put trans fluid in as this dose not work right with the system.

If you want "Locked" run the system in 4 low, as heavy off road in 4high with Quadra is not the best for heavy off road, use 4 low to that.

If you need more help just ask, I hope this worked.

1993 2HI N 4LO, 1998 5.9 LX Quadra trac with limited slips 2000 2HI, 4HI full 4HI part N 4LO 2002 Limited with Quadra with Vari-Lok differentials.

universal joint on the driveshaft may do this !
check transmission fluide as well.
good luck

1st let me make sure I understand your Jeeps 4 wheel drive. I believe the quadra trac system is a full time 4 wheel drive, there is no 2 wheel drive setting, only a separate 4 Lo (for very slow speed). If this is correct, the problem is, the quadra trac system you have is supposed to compensate for any variations in wheel speed, whether it's driving in the snow, or cutting the wheels sharply to park on dry pavement. What u describe is typical behavior of a part time 4 wheel drive system. The problem is, your full time 4x4 should be compensating for this, and it's not. So, let me know if the above info about your 4wd is accurate (no part time 4wd setting, no 2wd setting, only full time 4wd and 4Lo setting. If it is, the system is not compensating for changes in the wheel slippage correctly.

They didn't make Grand Cherokees in '86, so I assume you mean '96?

I'm also assuming it is indeed a 4x4 and not a two wheel drive...sorry, I have to ask!

All the V8's GC's were Quadra-Trac. Please confirm this with what is label on your shifter. If so, it should say "4Hi, N, and 4Lo".

The Quadra Trac system has a viscous coupling. Meaning, that when the rear wheels start to slip, it heats the coupling up, and engages the front wheels.

This system typically put about 95% of the power to the rear wheels, and only about 5% goes to the front during normal driving, so it's essentially in 2wd mode.

When you put the transmission shifter into neutral, and pull your transfer case down to 4lo, then you have all four wheels locked. Do not drive like this on dry pavement.

To answer your questions, the 4x4 should automatically engage when the rear wheels start to slip. It is a seamless transition and you really won't be able to tell.

If you're in real bad snow, then pull it down to 4lo. That'll lock all four wheels in and give you greatest traction.

Drive safe.