Jim Grant's Tech Tips
'98 Jeep Grand Cherokee
Q: Why does my 98 Jeep
Grand Cherokee have all four wheels engaged on dry pavement? It just started
doing this and seems to be ok on the road. When turning into a parking
space or any short turns you can tell it is in 4-wheel drive.
- Earl F.
It is likely that your Jeep has a model NV249 transfer case (circular
I. D. tag can be found at the rear of the transfer case). In your vehicles
4 wheel drive is full time ready but is rear wheel drive most of the time.
Most of the available engine torque/power is directed to the rear wheels
during normal driving. When the weather becomes a challenge a device in
the transfer case called a viscous coupler will direct the engine power
to the front wheels as well. The transition from 2 to 4 and back to 2
wheel drive is seamless unless the viscous coupler is starting to fail.
When a viscous coupler starts to fail they seem to like to lock into the
4-wheel drive mode and stay there. The fix requires a replacement viscous
coupler. In most cases this can be replaced without even removing the
transfer case from the vehicle. A word of caution, if the viscous coupler
is failing it needs to be replaced. Even though your vehicle is a 4-wheel
type vehicle is it not meant to be operated in 4-wheel drive all the time.
If driven too long in 4wd, damage to the drive train of the vehicle can