Changing the transmission oil is a tedious process that requires removing a total of 43 bolts ?an
d two panels.



So my friend and I came up with the idea of ​​creating a small window in the underpanel. This allows us to access the transmission drain bolt and filter by removing just 4 screws, saving us time.







We also installed a FUMOTO valved oil changer F303L on the transmission fluid filler port, drilled a 1/8 tap on the inside of the outlet port, and attached a Jiffy-Tite one-touch nipple.










We then used a 12V Oil Extractor Pump (about $20) to connect a Jiffy-Tite one-touch coupler to the end of the hose, and pressure-fed the transmission oil. This allowed us to fill 10.5 liters, which would normally only be possible from the top of the transmission. This eliminated the need for the tedious process of removing the air cleaner, among other things.

 

Cutting a hole in the shear plate isn’t a new idea, people have been doing it for years now. However, it’s a structural part, not just a close out panel. It takes me 2 mins to zip the bolts out with an impact, not worth cutting it up.

I did a similar thing with a Fumoto valve And a 2.5 Gallon Air assisted Mityvac.

 

I am unfamiliar with performing a trans fluid service yet. My car is not there yet. Where did you plug in the Fumoto fitting? What was there originally? Unless you are simply measuring and replacing the exact amount of fluid that came out while draining, I would still want to pull the fill plug to see the exact fluid level.

 

FUMOTO is attached to the side filler plug.
Starting with last year's model, the transmission fluid has increased by 2L, and since it is above the filler plug, it is no longer possible to fill it through the side filler plug; you need to fill it through the gold filler plug on top of the transmission. Or you can use the method we've done here.

 

I think so too, to some extent. Depends on whether the target is a normal fill, or a full track fill (exactly 2 liters above the normal fill). The normal fill is to the level of the fill plug. The track fill is exactly 2 liters above that for the earlier models, and the later models do not require a track fill. And for those earlier models, once the track fill is put in, it does not need to be removed for street use. From this, I conclude that a slight overfill is harmless for street use. But I do not think one would want to ever exceed 2 liters above the normal fill ever.

So, f doing a normal fill, measure what came out and just put in a little extra for a slight overfill.

But, if attempting a full track fill, I think more attention would need to given to the level, like you said. And for later models, the track fill is not required and not recommended. Josh Holder commented on that for the later models and said this about that: : "In the 2024 transmission? .......You could do it, actually you might risk some expulsion through the vent tube. It would be a wasted effort. So, I would not recommend doing it in a 2024."

 

My Dealer C8 Trained Tech has a somewhat unique way he filled my 2020 C8 DCT. Took ~5 minutes no pump needed! I watched. BTW, dealing with all the bolts is a non issue with a battery powered wrench, as he used.


He has filled "a few" transmissions over the years. Uses this method that took a total of about 5 minutes! He has a semi-flexible tube extension that "presses" into the 1 Liter bottle. Does not have to thread on, it's a rubber tapered bottom. An advantage of today's "thin for low cost" bottles (not quite as bad as some water bottles but easily collapsed.) After placing the tube end into the fill hole he just squeezed the bottle getting 90+% of the contents into the DCT. Then put the remaining fluid left in that bottle into the next bottle! I waited and was sure he would have to put some residual into an empty bottle. But never did, the residual left fit, into the next full bottle, there was room!


In year one of my 2020 C8 where I had the DCT filter changed on GMs dime, he just removed the aluminum panel and loosened the panel bolts behind. Had to fiddle to get the aluminum rear panel off. In year 3 he just removed both panels. Easy with his battery powered wrench!

 

The transmission fluid capacity has never changed. Early Stingrays required two liter overfill of fluid for tracking because a deficiency in the pan baffling. They fixed the deficiency in late 2023 and the two additional liters are no longer needed when tracking. The correct fluid level is when the fluid is at the bottom of the side filler plug.

 

Yes! I missed that! I rarely say this, but the statement in post 4 is totally wrong. And RKCRLR is correct.
The 2L overfill for track use became unnecessary because of change to both the case and pan that better holds the transmission fluid at the pick-up point for track use.

Here is Josh Holder complete explanation of that:Q::

Are the two additional quarts already there?

Josh Holder: It’s not really the case (meaning no). The case is, literally, changed for ’24. We did it because the Z06 necessitated a change in the lube system. Where we keep all the critical oil in a car on a Z06 that has so much lateral capability, was super important. So knowing that we needed to change the case and update the lube system for the Z06, in 24 model year, actually very late in 23 as it turns out, we moved all Corvettes to the same differential, er, the same transmission housing that the Z06 has. And when we did that you no longer need to add the additional 2 liters of oil. That (referring to the overfill) really was a way to keep (the) lube system healthy, lubrication where it needed to be, but it was overkill, it wasn’t kind of the way we would have done it starting over.

Q: Is the pick up point different – is that what it is?

Josh Holder: The pick up point is not really different. What is different besides the the size and shape of the case itself, which can hold more oil near the pick up point, but there’s baffles inside the transmission that under high G loading keep the oil near the pick up point, which is the whole goal of (the) lube system. So that’s the benefit that all Corvette receive in 2024 models.



Q: what if a guy (sic) did put the two additional quarts (sic) in there?

Josh Holder: In the 2024 transmission? .....…You could do it, actually you might risk some expulsion through the vent tube. It would be a wasted effort. So, I would not recommend doing it in a 2024. And honestly, when we recommended it in 2020 it was for a really extreme scenario, and in hindsight, I’m not sure we would’ve made the same recommendation. Its not easy to do for those that have done it themselves, a I’ve done it myself. Its not super easy. And so, we’re really glad that we got to take that revised lube system strategy to all Corvettes. And now anybody that wants to tracks their car or don’t track their car doesn’t have to worry about whether they have to add two liters or not and am I going to be that person that drives so extreme, maybe I need two liters, maybe I don’t. Takes that question out of it.

 

so good info on this getting close to doing this job.

 

My friend Takano-san has changed the transmission fluid changed in several cars.

four 2024 Z06s and four 2025 Z06s, two of which have the Z07 package, but all of them contained more than 10 liters.
That means they were originally shipped with more than 10 liters.

So how many liters should be added when changing the oil? Even if you fill it up to the point where it overflows the side filler plug, it will probably still be 2 liters less than the factory oil. This is very worrying.So Takano-san filled up the oil using the same method I used to fill the drained volume.

 

 

ALL C8s: Stingray, Z51 Option, Z06, E-Ray and even ZR1 and ZRX are shipped with the Factory Fill of 12 liters. BUT when replacing the Fluid ONLY ~10 Liters drain out. So about 2 Liters are left in clutch area, valve body, shift fork actuators etc. No way to get it out. Some more will come out IF you remove the pan.

For what GM thought was needed for some very aggressive Track driving they said add 2 OVERFILL quarts. There is no plug to check that level. So IF 12 Liters drain out "someone probably added 2 Overfill Liters."

TO ANSWER YOUR QUESTION:
Only add enough DCT fluid until it comes out of the ONLY Check/Fill plug. Now prior to the 2024 (late 2023 Z06) DCT cases GM had said 2 Overfill quarts should be added "IF TRACKING." BUT just before retiring the Marketing Manager, Harlan Charles said they were "Overly Cautious" and most folks Tracking would not have had fluid leave the pick-up. Josh Holder (current Chief Corvette Engineer) has said about the same and told a member they NEVER experienced a failure from not adding the 2 overfill Liters when testing. ONLY had an instrumentation indication. So if past warranty I would NOT add the 2 overfill Liters. Never with the new 2024 and later cases (which are built with baffles etc that have added assurance fluid will not leave the fluid pump pick-up area. BUT the new case has the same 12 Liter fill) . Now if a Pro Racing on slicks going downhill and exceeding 1.5 Lateral "g," "Might Consider."

 

See post 8. You should fill it to the level of the fill plug with the car level, no more, no less. And you need to check the level in accordance with the procedure in the manual which calls for the transmission fluid to warm and the run for three to five minutes while shifting the selector between D an R to fill the clutch circuits. The 2 liter overfill is specifically recommended against in the manual and was reiterated by Josh Holder (post 8).

The factory fill can vary so its possible that it is slightly underfilled or overfilled. But the instructions in the manual fill it to the level of the fill plug.

Slight overfill is not necessary but not harmful.

 

Interesting

 

What do you do with the waste fluid? Do the auto stores take that too?

 

Yes

 

Me too. There are several threads regarding this topic, a couple here , and a couple in the tech section. I have read them all and have gotten a good feeling about accomplishing the goal, and that it will work as intended. I have learned a little more about liquid dynamics than I need, these DCT trans are quite complicated. Sadly it will be lost on me soon. Good thing I can come back here to refresh my memory. It would be nice if someone could compile all of the different threads into one big sticky. Many thanks to everyone that has contributed to this important topic.