Rear end noise - whine

[pressonregardless]

OK, just to be sure I pulled the drive shaft and installed a new flex joint, had new center bearing pressed on and new center support, two new U-Joints. Really tightened up the drive line, so no more rup, rup, rup lurching in first when you let off the gas. Still have the persistent rear end gear whine under power above 45 mph. Let off on throttle or pushing in the clutch it is quiet, 4th or 5th still has whine under power so is definitely ring and pinion noise.

Question: I have changed the differential oil using 80W-90 gear oil GL-5(looked like original grey milky stuff when drained) and it quieted down about 20%. Is there an additive or a different weight gear oil I can try? The rear end does not leak and really don't want to go any further as there are no mechanical problems, just a loud whine by 55mph.

I searched the forum and didn't really find any conversations about different oils other than GL-5.

Thanks, Charlie

[majicwrench]

No magic additive. Certainly could be a gear whine, could also be the rear pinion bearing, which unloads when you let off the gas.
Years ago I had some old military gear oil, it was something like 150W. That might quiet it a bit, but hard to get moving

[TX82FIAT]

what year is your car. The later cars are know for having a weeker differential. from posts i have read the first sign the differential is going is a whine similar to what you are describing. Hope that is not the case.

[MrWampus]

Hey Charlie,
I had a 79 spider that did the same thing; a lot of whining and it was worse for me going around curves. I hate to tell you but my story did not end well. One day I turned into a steep up-hill driveway, dropped into first gear, gave it the beans and heard a loud clang like a church bell on Sunday morning. I wound up having to replace the whole rear axle assembly. You may be able to take pre-emptive action with your 74. I think the differential was more accessible in the early models than the later ones. Good luck with it, I hope your problem doesn't turn out like mine.

[Tobi]

My story is very similar to Mr Wampus's story. Three days of whining, steep hill, boom. Found lots of parts in the pumpkin.
I replaced the whole rear end with one I got on e bay for $80. No more u turns going 40mph for me anymore

[vandor]

Charlie,

As others said, likely there is no easy fix for your rear end, once a bearing is worn out there is not much you can do.

The only good news is that if your '74 has it's original rear end then the whole center section with the gears (pumpkin) can be removed without removing the rearend from the car. Then you can work change the bearings on your bench, or just pop in a good used unit.
Another option is to take the pumpkin to a driveline shop with new bearings and have them set it up.

[pressonregardless]

Thank you all for the replies! I did spot some GL-5 85W-140 at my NAPA store so may give that a shot for a little relief.....Rear End just feels too solid and tight to worry about a tear down. I imagine some of the unnecessary wear came from 35year old oil never being changed and it's degraded quality caused increased wear. Csaba, thanks for the insight, also I didn't connect Auto Ricambi was your store, but am now giving it a good look over for "goodies". Thanks to all that have help over the years! Charlie