Howling rear during deceleration

[Madkaw]

1983 4wd. 160k miles on chassis. Just put back on the road after engine rebuild. No prior history of the drivetrain. Transmission came from 2wd out of JY. Diff is 3.88 gear set.

Ive been breaking in the new motor with probably 200 miles on new engine . Noticed some driveline vibration at highway speeds. All tires were balanced. Felt like it could have been the driveshaft which I had done nothing to but greased. 

Now I am getting a rather loud howl , growl, noise coming from the rear during decelerations. No noise acceleration or with a load on driveline. I had put all new fluids in the truck before driving . Yes the diff gear oil looked nasty, but didn’t see any metal . I did change the pinion seal from where it looked like it had been leaking . 

Maybe I missed it but didn’t see where I had to set a preload on the pinion flange. 

Any ideas ?

[datzenmike]

Check the oil level... about all you can do from outside. Wiggle the driveshaft up down side to side at the differential. Any movement? I had a diff run dry and destroy itself. The driveshaft would flop around at the pinion seal..

 

Maybe the noise is the transmission so check the oil there too and for leaks.

 

Only other thing is the wheel bearings.

[Madkaw]

Thanks Mike. I’ll recheck transmission, but I know everything else is topped off. 

I do remember doing the axles seals and noticing one side the bearing seemed a little funky . Didn’t have the proper tool to do anything if I remember correctly. 

Ill try wiggling around things again, but the DS seems solid. 

[Madkaw]

Well I was able to get some wiggle right at the pinion, so something ain’t right. I guess I’ll pull he DS and take a look

[Stoffregen Motorsports]

Loose pinion flange? Bad pinion bearings? Does it leak any oil? This would be a sign of something wrong with the pinion flange or bearings.

[Madkaw]

It showed signs of leaking so I changed the seal when I first got the truck. Drove fine for over 100 miles. Maybe the nut came loose.