4WD Issue

Hey guys. First let me wish you all a very Happy New Year. So far, my new year has started on the wrong foot. After a night of partying and what not, I returned home today and received a call from my brother that his Selec-Trac 4WD was acting funny on his 97 Grand Cherokee. So I took it out to see what was going on. It shifts in and out of 4WD no problem. What's happening is a loud squealing sound from the front differential happens every time I hit the gas pedal when engaged in Part-Time or Full-Time 4WD. If I let off the gas, it stops. There is no sign of leaks in the front differential so hopefully there is fluid inside. I already changed the fluid in the transfer case and I want to change them in the differentials. Still being kinda new to all this 4WD stuff, what weight of gear oil goes into the differentials for these Jeeps? And also, what could be causing the very loud squealing? Any help would be great. Thanks guys.

Try Looking at your Belt.

MacGyver is right. When 4x4 fail, they "grind". Squealing is caused by something high rpmwise on your motor. A belt slipping is suspect, as well as a shot bearing in your water pump or A/C or Alternator or P/S pump or . . . Stick a 2' piece of fuel hose in you ear and point it here and there under the hood while your buddy sits behind the wheel making the noise happen. You'll find it for sure.

Post back with what your found.

CoachKarl

As to your question, the manual I have refers to using 80w/90 API GL 5 hypoid for standard use, 75w/140 API GL 5 hypoid for heavy duty (eg Trailering) use. If the vehicle is level and hasn't been driven for a while, a level check can be done with a 3/8's in rachet that will plug into the square-headed plug on the front, and a dull flat object to pry on the rubber plug on the rear. Fluid should be right at or just below the bottom of this fill hole. A full drain/fill usually required the purchase of 3 (didn't go all the way through the 3rd) bottles of the stuff. Also, I don't know what the temps are like where you live, but at 50 degrees, this stuff is like honey, so come prepared. I found a marine pump (the type you can get at Wal-Mart) makes things cleaner, but it takes quite a while. Here, have a link: http://www.4x4xplor.com/diff-service.html

My :2cents: on this is that there may be an issue with one or both of the CV halfshafts up front. That this happens only when the front axle isn't 'along for the ride' is what makes me think of this.

You also mentioned that you recently changed the transfer case oil. Be certain that you put the right stuff in there as well. My 99 GCL was making a higher pitch niose around tight turns. I couldn't believe it was the case but we changed the oil and it stopped.

Thank you CoachKarl, I've helped a lot of people out on the roads who think their machine is going to blow up or something and they were glad that it was that simple. I always start with simple before going into more difficult.
Later.

It is not the fan belt or anything like that under the hood because it doesn't squeal when the Jeep is in 2WD. It only squeals when it is in FULL-TIME 4WD. It doesn't even squeak in Part-Time 4WD.

I changed the fluids in both of the differentials and the transfer case. The squealing has minimized in the front when in FULL-TIME 4WD. It turned out the problem was the owner before me didn't use the 4WD at all and that the bearings in the front differential just needed new fluid to lube up properly. However, I am still having the problem with major vibrations: When I shift from any 4WD back to 2WD while the Jeep is in motion, the whole Jeep vibrates like crazy. I end up having to stop and try backing up and going forward over and over until I can pop the Jeep back into 2WD. So I am still stuck here and need more help.

sreilly 77,
Because the PO (previous owner) didn't use the 4wd that much, there could be a number of things to trouble shoot. I googled the problem and found another site with lots of writeups.I'm not a pro with 4wd in particular but figure this site might help out.
http://townhall-talk.edmunds.com/direct/view/.f0e6f51
Sorry I cant be of more help. Good luck!

sreilly 77,
Because the PO (previous owner) didn't use the 4wd that much, there could be a number of things to trouble shoot. I googled the problem and found another site with lots of writeups.I'm not a pro with 4wd in particular but figure this site might help out.
http://townhall-talk.edmunds.com/direct/view/.f0e6f51
Sorry I cant be of more help. Good luck!

I think I figured it out with that link you sent me. A lot of people on there are saying it is probably the bearings since the 4WD was never used. I'm going to try replacing them and see what happens. Thanks Macgyver.