Swapped tge original oil out of my 17 z06. Only had a little over 2 qts in it after a 30 minute drain. I’ve read tge factory had a habit of shipping cars with low oil. Replaced with oem 75-90 gear oil and have a definite hum in the back. Before I tear everything out to see what tge inside looks like what’s the heaviest oil I can safely run? How about a redline 85-140? The oem looks like trans fluid and thin af.

 

As far as I know, the low or no oil problem was with the 2014s. The 3.42 eLSD can take up to 2.96 qts (and the key words here are up to) which includes the fluid in the diff cooler. I don't know if all of the fluid will drain out of the cooler when you drain the diff. However, all of the Corvette diffs (mLSD and eLSD) that have a cooler hold about 2.96 quarts while diffs without a cooler only hold about 2.53 quarts. The Z06, GS, ZR1 and Z51 with Mag Ride have the eLSD diff with cooler. The Z51 without mag ride gets the mLSD with cooler. The Stingray without Z51 gets mLSD without a cooler.

Did you check the fluid level before you drained the diff? The specified diff fluid is the correct fluid. The GM Part Number fluid is a synthetic. You don't want to use the 85-140 since the diff isn't designed to use that fluid. After refilling the diff how much fluid did you get in before it started flowing out of the fill hole?

When I changed my diff fluid the fluid level was within a half inch of the fill hole and when I refilled the diff the lube was flowing out of the fill hole before the third quart bottle was empty. I reinstalled the plug and drove the car about 20 miles and then checked the fill level. As soon as I removed the plug fluid started flowing out. I don't know for sure but I am pretty sure I didn't get more than 2.75 quarts in the diff.

Bill

 

@Bill Dearborn I pulled the fill plug before draining and nothing came out. im not sure theres any way to check the actual level before draining. drained a little over 2 qts out. filled with oem spec ac deco oil which is super thin for a diff oil. took just under 3 pts to run out the fill hole.
no way to tell if my car left the factory low on oil but with only 15500 miles on the car im going to guess its never been changed. the noise in the rear is substantial to me its not brakes im sure its rotational sound again im sure of that. little to no sound under 30mph over 40 mph its a pronounced whine in the back.
I may have a friend drive the car so I can reach into the back with my phone and try to record the sound for dissemination. my main concern is im going on a 2000 mile road trip in less than 2 weeks and would prefer not to 1. hear it and 2. have this worry in the back of my mind during the trip.

 

I change the diff fluid every engine oil change. I don't know what comes out, but it always takes just shy of 3 quarts going back in.
Of interest, the M7 is almost exactly the same...just shy of 3 quarts to refill.

 

im aware of how much oil is needed im trying to see if there's a thicker alternative to use to try to cut down oil some of the noise im hearing . if not then im going to have to yank the diff and open it up to see because its definitely making noise.

 

[QUOTE=9sec;1606351241]I'm aware of how much oil is needed I'm trying to see if there's a thicker alternative to use to try to cut down oil some of the noise I'm hearing. if not then im going to have to yank the diff and open it up to see because it's definitely making noise. QUOTE]


If it's making noise now it will be time to open it soon enough to tell what's going on.

Been there, done that. Good luck.

 

[QUOTE=Thomasmoto;1606354340] in the back of my head im thinking thats what's going to be needed. in the interim I ordered 3 qts of redline 75-110 pls-5 gear oil. supposed to be a nice medium between 75-90 and 80-140. has friction modifiers and is supposed to be the go to oil to quiet down a noisy diff. we shall see

 

The answer to that is a definite "no". Once it starts whining you need to rebuild it. You will need new ring and pinion as a minimum.