'90 XJ 4WD 'Whirring' sound when decelerating

Hey guys. Looking for some help/opinions. Yesterday my 1990 XJ AW4 I6 NP231 started whirring on the way home from work. This noise only happens when not accelerating and ONLY in 4WD.

In addition to that, my 4HI hopped into 2WD with my 'PART-TIME 4WD' light STILL illuminated... It stayed this way for about 5 minutes. Only after shifting to 2WD and back to 4HI a few times did it finally register and correct itself.

Any ideas on where to start?? You're help is appreciated. Thank you.

Well, your dash light is vaccuum actuated, check your vac plug on your axle.
When was the last time you changed your t-case fluid?

Those switches like to "crap up" overtime. Just pull the switch and clean the ball on the end so that it moves freely.

The front axle is engaged in 4WD*. The noise is probably from the differential gears rubbing on the coast side, although there is also a small chance that it could be the front u-joints since they are stressed differently when loaded. In 2WD the front axle also spins but the driveshaft isn't loaded so there is no resistance. In 4WD there is coasting resistance.

*4WD means both driveshafts get power, and the axles distribute the power to one or both wheels. At least one wheel on each axle will spin at the same rate as one of the wheels on the other axle. You shouldn't drive around in 4WD unless you are on a surface that allows the wheels to break surface contact easily.

I was gonna change fluids this weekend. That's step number one. I'll clean the 'Part-Time' switch as well.

ehall said:

The front axle is engaged in 4WD*. The noise is probably from the differential gears rubbing on the coast side, although there is also a small chance that it could be the front u-joints since they are stressed differently when loaded. In 2WD the front axle also spins but the driveshaft isn't loaded so there is no resistance. In 4WD there is coasting resistance.

*4WD means both driveshafts get power. You shouldn't drive around in 4WD unless you are on a surface that allows the wheels to break surface contact easily.

Click to expand...

I was driving in snow, not dry pavement. Good to know though about the coasting resistance. Although my Jeep has never made this sound before.