whining noise when accelerating - from where?

[cdub2010]

I have finally got my truck drivable after a year and a half of fixing a ton of stuff. Now im chasing down a whining noise when accelerating from 20 to 60 mph. The noise seems to get louder the faster I go. It goes away when I let off the gas. I havent gone over 60 yet, still in shakedown mode.

Background info is the truck is a 71 LWB 2wd 350/350 with 3.73 open diff. It has had a serpentine setup from a 90 chevy with new alternator, fan, fan clutch and waterpump. The drivetrain has new flexplate, rebuilt th350 with new converter, re-balanced drive shaft with new carrier bearing and new u-joints, the rear axle fluid changed. Rear gears were a bit rusty from sitting for so long, looks like a few teeth are lightly pitted but no chips or bigger damage.

any ideas?

[Stocker]

Just a guess.... being speed-related (20 to 60 mph) and only when accelerating, it may be the differential.

[Marine-58]

More than a few years ago I had a similar issue on an inboard boat engine. Turned out to be a vacuum leak between the intake and head. Tightened down on the bolts and it got better but had to replace the intake gasket to make it go away.

I was only 14 and learned how to properly install an intake from that experience...

[demian5]

Originally Posted by Stocker

Just a guess.... being speed-related (20 to 60 mph) and only when accelerating, it may be the differential.

I 2nd that.

[Wrenchbender Ret]

My vote is for the rear end. Check for any looseness in the pinion brgs. If that's OK pull the cover back off & check for any side to side motion in the carrier. If that's OK check the tooth contact pattern in the ring & pinion.

[truckster]

Originally Posted by Wrenchbender Ret

My vote is for the rear end. Check for any looseness in the pinion brgs. If that's OK pull the cover back off & check for any side to side motion in the carrier. If that's OK check the tooth contact pattern in the ring & pinion.

My first thought was the pinion bearing. Most likely culprit, in my opinion.

[nevada]

Its the Rear Diff.

mine does the same thing, whines louder as I go faster, take foot off gas, sound goes away....my 72 C20 with 4.11 rear gear, piñion is worn. trucked lugged a heavy 10 ft Alaskan camper in back its whole life, just had the motor worked on.. new cam and lifters installed this week and motor sounds smooth. still have the rear diff noise. won't hurt anything if not being used to work hard towing or hauling (camper is removed now)...I'll let mine whine for another year until I can afford to have a 700r tranny installed and will have the worn 4.11 pulled and install a 3.73 at that time.

[weq92f]

Sounds like gear whine.

-klb

[Shinysideup]

Did you replace the pinion seal when you were into the differential?

[cdub2010]

Originally Posted by Shinysideup

Did you replace the pinion seal when you were into the differential?

no, there were no leaks from the pinion, just changed the gear oil. I cant move the pinion yoke in or out with the driveshaft removed.
Its quite loud around 45, guess ill get on the radio install.

[cypressbog]

I had the same thing. In my case it was the wife bearing. Bought her some chocolates and flowers and the whining went away for a while,