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Discussion Starter · #1 ·
I've got a 2021 Z71 that I got in November with 27 miles on it.

Being a believer in changing fluids early and often since oil is cheap and diffs/transfer cases/transmissions/engines aren't, I planned on changing the diff oils at 5k miles (ended up being 6700 due to travel that took me up and down the US this month).

At any rate, when I went to drain the rear diff, lo and behold...Chevy took the drain plug away. I found an other forum where a guy with a 2021 ZR2 discovered the same thing. I guess this is a "new" change with the 2021 model year...Ya:rolleyes:

So, in the (likely) quest to save a $1, a simple and easy 15 min job (wouldn't even need to move the spare) was turned into a messy, pain in the ass hour long job by the geniuses at GM. Thanks guys!

But, instead of just bitching, I'll add a little bit of tech for those that have never changed diff oil by removing the cover...

I got my fluids from the dealer. There are a bunch of threads which talk about what you can use for the diffs and transfer case, but none of the oils were local to me, so I just went to the dealer. I paid ~$20/qt for the 75W-90 (got 4, only needed 3) and ~$7/qt for the ATF for the transfer case (need 2). I won't cover the TC and front diff since there are write-ups/videos that cover those.

The gasket on the rear diff cover is re-useable, so thanks Chevy for that small gesture.

Tools needed: 3/8" wratchet, 3/8" torque wrench, 13mm deep socket
Optional tools: impact gun, 3/8" extension (4"), standard 13mm socket

Start by digging out the tire iron from under the rear seat and lower and move out of the way, the spare tire.

Always, always start by making sure you can remove the fill plug (underlined in red). It really isn't a big deal since we are removing the cover, but it's good practice to get in to the habit of doing it first to make sure you can remove it. Wipe off the metallic shavings off the magnetic plug.

Now, remove the vent tube. It just pulls off the stud (circled in green), then take that nut off (13mm) and remove the bracket. Then loosen the stud (I didn't remove it until completely drained - see below).

Next, put your drain pan under the diff and remove the lower bolts that hold the cover in place (yellow). I removed the lower ones first, then moved to the top ones (Note: One bolt on top has a bracket for the brake cable (blue)). I left the top stud (green) in so the cover wouldn't completely come off while draining the oil. I gently pried the side of the cover to loosen it from the gasket to aid in the draining of the fluid.

Once drained you can completely remove the cover and inspect/clean the diff/diff housing. I wiped down the bottom of the housing and the inside of the diff cover, but I really didn't need to do it; there weren't any solids. I was at 6,700 miles - YMMV.

Put the cover back on and rebolt. I used a generic star/alternating side pattern to snug up the bolts and then torqued to 24 ft-lbs.

Next refill with the oil until it dribbles out the fill hole (about a quart and a half). I put teflon tape around the fill plug and put back into place. I didn't torque it, just got it in there snug.

NB: Don't use those little pumps you screw on the bottle, unless you are wanting to practice that up and down motion with your hands. Get a 1gal garden sprayer at LoweDepot for $10. Cut the wand down to just a few inches and bore out the nozzle with a drill. Much easier to dispense the oil. I've got two - one for gear oil, the other for ATF.


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Thanks for the write up and I concur about leaving out the drain plug. GM is getting to the point of wanting to leave all access for maintenance off to save a buck, this will force most to give up and take it to the dealer.

Soon next they'll leave the fuel cap... oh never mind they already did that as well....
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