Drivetrain Howl on Decleration/Coasting-Bad 12-Bolt?

I've got a 12-bolt GM axle from an 81 Chevy installed in my 50 Chevy truck. Lately I've noticed a pretty good howl/whine when I let off the throttle/coast. Accelerate, and the noise goes away.

The noise seems loudest around the trans, but notice my rear axle pinion seal is leaking, which could indicate a bad pinion bearing. I replaced the pinion seal before I installed the axle, and was careful to install the nut in the same position (number of turns) as before removal.

Is the noise more likely to be from the rear axle than the trans? I would think if it was the trans I would hear it under all conditions, not just coasting. Obviously I have a pinion seal issue at a minimum but was wondering if I need to be looking at the trans as well.

Thanks in advance.

Joe.

I would check the pinion nut first, they are known for getting loose. GM recommends replacing the nut if it is removed.

The rear diff on the 1982 GMC K1500 I once owned was always noisy - for as long as I owned it. Pulled it apart a couple times to replace seals, check bearings and change the lube. Even installed a new yoke and crush sleeve once. Luckily, the noise gradually subsided over time and miles. Looking back, I probably should have taken it to a pro shop for a pro rebuild. Correctly setting up the wear pattern on the R/P usually cures a noisy rear diff.

Jim

Tightened the pinion nut and all is quiet now. Hopefully I didn't trash the seal - I'll see if the leaking quits.

Thanks for the suggestion! That wouldn't have dawned on me until I went to R&R the bearing. Looks like I need to get a new pinion nut.

Joe.