: Why does fresh lube make diff quiet?

11-03-07, 12:26 PM
My diff was singing louder than the soprano in our Church choir. I actually wondered sometimes if people in the next lane could hear from their cars. I'm serious....it was that loud (while decelerating). I just changed the lube an hour ago and went for a drive......Truly reduced the whine by 50%. I'm a damned good pilot, but not an oil engineer. Can any of you REALLY smart guys (Randy????) tell me why that happens? I only had 3000 miles on the "old" lube. Just curious....there has to be a logical reason. (Does it "wear out")??

11-03-07, 12:42 PM
Well, I am not one of the smart guys, but I have submitted by diff fluid for analysis. That analysis indicated copious amounts of iron (presumably from gears or bearings) and copper (presumably from bushings). In my case the lube change did not affect the noise level.

11-03-07, 01:37 PM
Hypothesis - The additives in fresh lube haven't yet been broken down by heat.

11-03-07, 06:31 PM
Your original lube level might have been a bit low.

11-03-07, 06:48 PM
Its not Robotussin. I'm a firm believer that 'Tussin makes it all better. J/K You are right though on the real. When changing fluids it does make the volume go down. Mine is starting to raise its voice again. After I took off the Kars stage III it was silent. Now that I drove around in another car for a week it is loud to me again. Maybe we are just anal, but one can never been too carful when skating on thin ice.

c5 rv
11-03-07, 07:24 PM
Has anyone tried Schaeffer's #267 or #268 gear oil? The GMC AWD folks like this and it quieted the rear end of my 81 vette.



11-03-07, 07:36 PM
... REALLY smart guys (Randy????) ...You can't be serious! :eek:

First of all, you've posed an interesting question because this has been talked about before, but no one has explored what's really going on and why it seems to occur. I like the answers, above, so far, too.

If I'm really smart, I'll just :food-snacking: and keep refreshing the screen.

11-03-07, 08:01 PM
Next time I change the lube, I will use this stuff

Schaeffer's #267 or #268

Randy, I am serious! ! How smart can I be??? I have three (3)......not a misprint ex-wives.....WTF????

Thanks Guys for all your inputs.

11-03-07, 08:07 PM
Not 100% sure either, but my C6 had an ear-popping whine at 20K miles, took it in to dealer, they changed fluid and included additive and no noises at 34K miles. Never heard a whine in the V's rear as the motor/exhaust is too loud:cool2:.

11-03-07, 09:20 PM
Hypothesis - The additives in fresh lube haven't yet been broken down by heat.

Interesting theory....plausible as well....at least it sounds right....hey, maybe we could submit this to the mythbusters???

11-03-07, 10:48 PM
yeah dude thats a good idea.