My 94 Grand Cherokee Laredo has fulltime four wheel drive. The knocking I hear from the front drive shaft when I make sharp slow speed turns(parking), leads me to believe the viscous coupler is shot. When I am driving at any speeds above 20, I hear nothing and the car drives great,which makes me think the VC is only activating when I turn sharply at these low speeds. Is this true? Am I doing any damage to the transfer case with highway driving. I would like to wait a month to get the car repaired.
Given its location it sounds more like a worn CV joint not the VC which is in the center usually of the vehicle behind the transmission.
A worn CV joint can be dangerous. It won’t get better by itself.
Check for a CV Joint Boots being ripped, that will clue you in.
The VC can start to fail over time, and is one of the weak parts of the NP249 transfer case. One of the symptoms is wheel hopping in the front when making sharp turns because the VC is not allowing the front drive shaft to spin faster than the rear drive shaft (it’s locking up). But, andrew_j could be correct also.
One way to diagnose the VC problem is to let the Jeep sit in a parking lot to cool down. Start up and do several figure 8’s. If you start to get hopping after a bit, then it is most likely the VC. If the problem shows up immediately, it could be the CV joints, but it doesn’t rule out the VC.
I am pretty sure it is the VC. The Joints and boots are in good shape, and the noise is coming from the transfer case. I imagine I will drop in a transfer case, although i have not decided if I will stay with the 249, or switch to the 242. What I am curious about is if I can drive it for a month without destroying the transmission.
The VC won’t harm the transmission. But you are putting extra stress on the drivetrain when you turn (that’s why the wheels hop to release the stress). If you keep the 249, you only need to replace the VC, not the entire transfer case.