I have a 1998 Jeep Grand Cherokee. It is an all wheel drive but is 'stuck' in 4 wheel drive. All the tires are the same size; Is there any way to 'disengage' the 4wheel drive?

that is because you have Part time 4wd? (what do you have)?
and must not drive on pavement free of ice.
its now winding up the drive train, bad for it too.

drive, to dirt, sand, gavel or grass and shift out of 4wd.
or jack up 1 tire, and same,
one tire must be on slippery surface. at least.

http://www.rubicon-trail.com/4WD101/driveline-bind.html

this happens on all PT 4wd
or using LOCK on AWD. dont.

Hi there:
Your VIN code refer at one 1998 Jeep Grand Cherokee Laredo 4x4 4.0L 6-cyl. Quadra-Trac, then, according with this, you must pay attention to the Standard tire size (in case of different tires in front and rear the dimensional data are valid for driving or rear wheels):
Standard tire size: P 215/75 R 15
Tire width (mm): 215
Tire sidewall factor: 75
Rim size (in): 15

Total wheel diameter (mm / in): 704 / 27.7

Hope this helps.

If it is not still in 4 wheel drv then i wouldn't worry about it as long as you know that its out of 4 wheel drv.

Tire size is critical on any jeep but especially so on ones with quadratrac transfer cases. If you run different size tires it will cause the fluid coupler inside the case to overheat and fail. (big$ to repair)
Don't drive it that way and get a matching set of tires on there asap!!!

At least two and if you have all time 4 wheel drive it is extreamly important that you have the same size tires on both sides as if not you will ruin your differential ( also check spare size as you dont want to be stranded some where with out it)

If your in 4 low be sure to shift into nuetral first. Otherwise try backing up while shifting to 2 wheel drive

Four low is almost never used. I use it on very steep rocky or muddy trails in the woods or to pull someone out of mud or a ditch. Though some will shift standing still it is best do do this while rolling. Four high can be shifted at low speeds of 2 to about 35mph (higher also but not really good idea) Low can only be shifted between 2 to 10mph. If you find yourself stuck and unable to shift because you aren't rolling you can also turn the engine off, engage the transfer case and re-start. That avoids having the gears clashing together. Best rule is if it begins to grind, don't force it.

You cannot drive with different size tires front and back, especially with full time 4x4's the tires travel different distances when rolling.. a one inch height difference translates to a three inch rolling difference...ten turns of the tire = a thirty inch difference in distance traveled between the front and rear of the vehicle..being all attached to the same point (the transfer case) there is no way to compensate, therefore something must fail or the vehicle will stop in a locked up (bound up) condition. The weak link is the viscous coupler in the transfer case...likely what has failed.

make sure your tire pressures and sizes are all the same then try backing a go froward while turning. and moving the shifter in and out of 4x4. if that does not get it then get all 4 tires off the ground with jack stands and allow the wheels to turn slowly while you move the shifter in and out of 4x4. USE CAUTION IF SPINNING ALL 4 WHEELS OF THE GROUND. if that does not get then the t-case will likely need to be disassembled and looked into.

I'm not absolutely sure on the tire size for the jeep itself, but I think they are 225/65/R15's. Not absolutely sure.

As for the noise, from your explanation, it sounds like the transfer case is under a heavy bind. Take it off of the road in some grass or dirt and then move it forward a few feet then simply hit reverse. Don't move much maybe an inch and it may release the bind. Once you get the bind off the transfer case, it should slip out of 4wd, unless there is damage in the case/shifter itself.

When operating four wheel drives, with tires of different sizes it causes extreme stress on the gearing in the transfer case. Larger tires don't turn the axles as much as smaller tires. So, this causes stress in the driveline as the front is actually turning slower then the rear. In turn, this will put so much pressure on the gears that it could cause damage and the shifting mechanism will not work correctly to pull it out of 4wd engagement.

Try those ideas, and see if you can get it out of 4WD. Definitely put four tires on the jeep that are all the same size. This will keep you from having excessive stress on the transfer case and gearing therein.

I hope this helps out buddy.