I have a 1999 4x4 Expedition & I am trying to locate & fix a whining noise coming from under the rear end. I have 119,000 miles it happens after the truck is warmed up and cruising at 10 mph and up & I do not believe it is brake related. I was getting a vibration at 70 mph & deciding to try changing both u-joints on the rear drive shaft. The vibration has gone away, but the whining noise is still present. Any common problems in the rear end I can check?

Thanks,
RH

 

Could be worn out bearings in the rear differential. They whine or humm. My friend's jeep has some bad bearings in the front differential and they're louder than the tire roar on my mud grapplers

 

A whine or a drone-howl at a certain rpm indicates the pinion bearing pre- load is a little out.

What happens here is the pinion gear is not centered on its plane in relation to ring gear gear. At a certain RPM there is a resonance or harmonic that is generated or a howl like drone noise.

Check your inch pounds of pre load on the input yoke of differential. Take off wheels, and ideally the rotors ( or drums) and of course lay drive shaft aside. Check to see how much torque is required to move the axle.

Adjust torque wrench to a break over feel, and check in both directions.

I forgot the spec. on *used bearings* for this check. But be careful because you may look at the new number setting.

The tricky part is to tighten this correctly, i.e. not to over tighten because once you do this you will need to replace the crush washer and start over.... really a nice way to ruin a weekend.

 

I will check when I get a chance. Thank you for the replies.

 

I would pull the rear cover and insert a pry bar between the ring gear carrier and the axle center section. See of there is any movement of the carrier. If there is side movement of the carrier (still installed,), this is indicative of a potential bearing problem on the diff. carrier or perhaps a taper bearing on the carrier is creeping or spinning on the diff. carrier journal. With the cover off: look at the tooth surfaces of the ring gear and glance in at the tooth surfaces of the pinion. How do they look? Can you still see machining marks on the ring gear? Looks for chips on both ring and pinion. Look for excessive shine on the ring gear. Look for crows footing on the ring gear (indicative of a previous low or improper lube condition).