These photos show the amount of metal particles that were trapped by a Gold Plug after about 3000 miles. Started with new Delco grape scented fluid. Plug is in fill hole.

 

Hate to say it but looks like you may want to go ahead and drain that one again - twice. Dump a few quarts of clean fluid through it as you are draining it, and let it all go to waste. This will help flush what ever gunk is laying in the bottom of the pan out, and top it off and run it again. If you find that much metallic particulate in the next flush it may need further investigating.

 

INCORRECT STATEMENT and ASSUMPTION..........................

where do you think any particles from any NORMAL WEAR of the bearing races, bearing rollers, or gear material end up...............................

on the DEBRIS magnet......................

sorry to correct you, but analysis of differential assemblies is what I do for a real world living.............

 

I bought the car in August of 2015 with 77k miles. The GM VIS report showed a fluid change at 50k. So shortly after I got it , I drained the fluid and filled with Mobil 1. Drove it for 2 weeks, drained and put the synthetic AC Delco stuff in with a 4oz bottle of GM additive. I now have 83k miles. Cleaned the magnet about 3k miles ago and again today. This is a very strong magnet. I am a bit surprised there is that much stuff on there, but another poster doesn't think it's abnormal. I'll keep an eye on it. Thanks

 

I just changed the gear oil in the rear diff of my 92 Camaro a few weeks ago with 102,000 miles, it was the original fluid which was pretty dirty naturally. Fortunately removing the rear cover makes cleaning things a lot easier with a can of brake kleen and an air hose to blow everything completely dry. I then removed the cover a few thousand miles later to install a limited slip unit. The magnet on my aftermarket cover was spotless, the oil looked like it was just poured out of the bottle and everything inside appeared to be brand new. That is the luxury of having an old axle where you can remove a cover and access everything easily to clean it. Not the case on a C6.

On the C6 corvette things are much different having only a fill, and drain plug to handle fluid changes. It's convenient, but it's not possible to get all of the particulate out of the differential by simply draining the fluid. I didn't mean to cause alarm by stating that his differential needs work - the point of my post was that if you want to clean it out the only good way to do that is to have extra quarts of fluid on hand, and pour them in so they wash the unit out as the old fluid is draining. This avoids any unwanted chemicals being introduced to the unit and gets rid of a lot of the debris the OP is seeing on his fill plug magnet.

I do indeed think what you are seeing is normal wear but from fluid that's already been changed twice there's no reason to see that much on a magnet after 3000 miles of driving unless all of the oil fluid wasn't flushed out - which is what you wanted to do.

Sorry to be confusing in my original post.

 

No worries. I think I'm going to try the Amsoil stuff soon. As inexpensive and easy as it is to change, I think it's good insurance. Best regards

 

Not sure what all the fuss is about - you have a posi unit in the rearend that is made up of semi metallic discs that are designed to slip at a given rate to do their job.
You will always have some metallic particles with posi units.
Be careful switching the rear fluids around from what GM recommends - I have seen several rear-ends destroyed by use of improper oils and or lack of friction modifiers.
Lots of funky loads occur in a rearend and again those clutch packs need to be lubed in a certain manner to perform correctly.

 

You put in the wrong stuff the last time, so why would you want to do it again?

The correct fluid is Dexron LS gear oil 75W90 P/N 88862624
It contains the correct amount of friction modifier. Do not add any additional friction modifier.

BTW, the service frequency is 150K miles.

 

I'm worried about you my Corvette brother! Your a mean man. Do you really think I would deprive my baby of grape scented fluid?

Seriously, the manual says to use synthetic 75/90 with 4.7 ouces of additive. I used Delco 88900401 and Delco additive. Car is a very early 2008 model.The fluid you mentioned is not synthetic if I remember right. It's too cheap and easy to change to let it go more than 50k - in my OCD mind anyway.

Best regards

 

direct from a GM Technical Service Bulletin.........................

For 2006 Chevrolet Corvette Z06 and 2004-2006 Cadillac XLR, 2006-2008 XLR-V and 2005-2008 Chevrolet Corvette (base model/non-Z06)
Drain and refill the rear axle fluid. Refer to Differential Oil Replacement in SI. Use the DEXRON® LS fluid listed below. This fluid already contains limited-slip friction modifier.

88862624 (U.S.)
88862625 (Canada)
DEXRON® LS Gear Oil 75W-90
As Required

 

I haven't had any noise or clunking sounds. I think that's why they changed the specs. I don't guess leaving the synthetic in there will do any harm. Thanks

 

just a FYI - synthetic lubricants and mineral based lubricants react differently on seals and other internal components.................... if an assembly is originally designed to operate with a mineral based lube, and then gets drained and refilled with a synthetic based lube it is possible for seal leakage and other adverse reactions to occur..........just stating facts

 

Check GM Corporate Technical Service Bulletin #07-04-20-002A dtd 01/09/2008 that supersedes the 2008 Service Manual and TSB #07-04-20-002 dtd 04/16/2007, which indicated the use of supplemental friction modifier. Your early '08 MY factory fill was the 2-part method, while the changeover for the one part factory fill happened in late Oct/ early November '07.
I don't remember what it smelled like when I changed it.

 

That's the reason I used the one I did. My owners manual specifies synthetic. I guess GM decided to switch to the other. Maybe the new spec is synthetic, but it doesn't say it on the bottle. - at least not on the front. Thanks

 

The new stuff is the same as the 2-part formula, but pre-mixed in the exact ratio to ensure proper gear and bearing lubrication and the required slippage needed for the posi-traction clutches. I don't know if the ratio is the same as the 2-part method, but rest assured it works best. Too much or too little of the friction modifier will result in excessive wear.

 

I think you all have convinced me to go with the one part stuff. It will be interesting to see if there's fewer particles on the magnet with it. This is the one I used. Notice the grape scent.

 

This is what you want. Notice it says Dexron LS Gear Oil right on the bottle. Link is just for reference, may be cheaper elsewhere.

 

 

Personally, I don't think that there is anything to be worried about here, but if you are concerned, I would suggest sending a sample of the oil to Blackstone for analysis...(note the first four letters...LOL). The correct fluid is Dexron LS, not a fluid that requires adding a slip component.

 

On behalf of information shared by rkj427 and myself, you are welcome.