ajrothm

After reading all of these reports of the diffs being under-filled, I decided to check mine. I couldn't feel anything with my finger as far as I could get it in the fill hole so I decided to drain/change it.


Here is what I got out of it:


Looks like about 2 qts or a little more....so it seems to be 1 full qt low.



Nasty nasty stuff for only having 2k miles on it.



Fill plug ^^^



Drain plug ^^^

No significant metal but definitely a good amount of glitter/sheen in the oil. My rear end is dead quiet and has 2065 miles on it.

After seeing how the fluid looked, I'm glad I changed it, if anything for my own piece of mind. It took exactly 3 qts to fill it until it ran back out of the fill hole.

My local dealer had the correct gear oil in stock.. $87 for 3 qts.


So I definitely recommend checking your fluid level at a minimum but honestly, I'd change it if you have cleared the 500 mile mark...Just my opinion,

silver74vette

Great write up and thanks for the pictures.

is there a procedure for filling the cooler and rechecking like on my 2012?

Thanks, Chris

Kaged

Just checked mine in prep for a track weekend. Was over 8 ounces low and still about an 1/8 inch shy of the top of the fill point after adding that. Interesting that the owners manual says anything within 13mm (1/2 inch) of the top is acceptable but the service manual states 1/4 inch minimum.
Did not have near as much "gray matter" on my fill plug - FWIW.
Will be changing the fluid after weekend.

juanvaldez

'Xactly what mine looked like. That shimmery stuff is some kind of break-in lube. Looks like GM assembly lube/oil additive.

ajrothm

I did not doing anything to drain the cooler etc.. I figured whatever is in there, is in there, its not gonna hurt it.

As far as refilling. The manual says to fill it until the level is even with the fill hole threads, install the plug. Then jack the wheels up, start the car and run it in 2nd gear for a few mins, shut it off, let it sit for 1 min, then check the level again.

*** I did NOT do this***
Its too big of a pain in the *** to find the level in the diff with your fingers (unless you have baby hands with freakishly long fingers) so I just drained everything I could get out of it with the diff HOT (I drove it 20 miles prior to draining), then refilled it until it puked pretty steadily from the fill hole, put the plug in and called it good.

Either way, it has 1 qt more in it now then it did before so.....Its good enough for me. The cooler may still have some old stuff in it and the hoses but...I'm not worried about it. At least 98% of the fluid is fresh and clean now with no break in material and clutch material.

Joy c7

Thanks for infro we will change ours when we get it out this spring.

robert miller

All that hard azz driving lucky it still has a rear end diff under it. Just kidding buddy mine didn't look that bad but was bad and was also low about the same amount.

I went with amsoil with the additive also in mine. Plus I did LG auto trans pan and did my trans at the same time. Also used AMSOIL in the transmission also. Robert

ajrothm

LOL..

I haven't beat on this one TOO bad yet. 6 passes at the drag strip...2 runs up to 160 mph on the streets of Mexico, and a hand full of highway bombs to 145 ish... That's about it. That's pretty light for me.

But yeah, I changed it for piece of mind... I'm old school like that. You never leave break in oil in engines, manual transmissions or differentials after 500 miles or so..... Now auto trannies, I normally don't change the fluid in since they have nice big paper filters and lots of fluid in them... I figure the trans will likely go out anyway before the fluid gets too dirty.

GHALL777

Changed my differential fluid at 700 miles. I wanted to only check it but it does take some effort to removel the fill plug so I decided to change it. I got out 2.2 quarts so it was roughly 0.8 quarts low. The fluid didn't look too bad though it had the metal sheen. Bought the GM fluid at Amazon to save a few bucks.

robertbruce

I bought 3 quarts of ACDelco 10-4034Dextron LS 75W-90 Gear Oil 32 0z on Amozon.Com this morning. Paid $13.52 a quart, taxes, shipping and handling total for everything was $49.14

ajrothm

Yeah you can definitely save some money buying in online.

This was a spur of the moment deal for me today on my one day off so, curiousity was killing me if the diff level was low so....I was just going to check it initially, but as I drove by a dealer I thought I'd swing in and see if they stock the fluid and they did so...I said screw it, bought 3 qts and ran home to change it.

My rear end is very quiet, and I'd like to keep it that way, instead of continuing to drive it around a quart low on fluid....especially since the rear diffs are apparently on back order...(according to the dealer I spoke with). I'd rather prevent a problem then have to deal with it later, especially on a major component.

I could have had the dealer top it off for free but...I wanted to see the sauce for myself and measure it.

robertbruce

You got the job done and that is all that counts! I was just trying to save money for the next guy.

Joy c7

Just ordered 3 quarts. Thanks!

BOBSZ06

Same here....Daves!

5thGear

I really believe that everyone should consider replacing the diff fluid at 500 miles. New diff will run hot during break in. Had diff replaced under warranty on my 2016 Z06 due to loud whine sound. Fluid was low.


On my 2017 Z07 I had them check diff fluid during PDI and they added a little. Ran the car three 20 miles trip and had it cool down completely after each trip. Then changed the fluid at 500 miles and again after the first track days. It might be an overkill but rather do this than having a diff replaced on a new car again.

LuckyC7Z06

Dang it see what you did?! Just ordered my oil on Amazon also. I have 10k miles on mine and I drive the hell out of my car so I'm wondering what it'll look like.

spearfish25

I've changed my diff fluid a few times. Here are some tips:

1) you can do it without the car raised up if you're a 'smaller' human.

2) the fill and drain screws fit 3/8" ratchets directly.

3) if you get an angled head 3/8" ratchet THAT LOCKS THE ANGLE the fill screw is much easier to remove. Home Depot has a Husky model that locks the angle and works great.

4) while the manual says to run the car in 2nd gear and then recheck, I've never needed to add more fluid. This is confirmed by getting back under the car, continuing to fill the diff and getting fluid dripping out immediately. Thus if you add almost exactly 3 quarts on the initial fill, consider yourself fine.

5) the transmission is different and I was able to add more fluid after running the engine for the specified 2 minutes.

hcvone

My C6's and C7 have been much better from the factory, some of my C4's and C5's were WAY under filled.

GOLD72

Anyone know for sure if checking the tranny and diff fluid levels are on the NCM PDI check list for R8C deliveries??

Turbo Bob

Great info Alan. Thanks for the write up. Time to change my rear diff fluid.