I pretty much followed the SIX service manual procedures that are invoked. I've attached them for other people that want to do this on their own. What is unique is how I got the fluid in. I used a garden sprayer that I purchased to dedicate for changing DCT fluid. I cut off the tip and used a couple pieces of Tygon tubing I had laying around. The larger collar seals the filler plug hole so fluid doesn't run down the smaller tube. Next time I may make more of a U shaped end so the fluid doesn't want to run down the side of the tube. The problem with sealing the fill port is you don't know when it is full. There were wires or something partially blocking the fill hole so you need to be careful not to damage them. And if you use a collar make sure you don't push it all the way into the port (that would be bad).
I also used a piece of bailing wire that I looped around the handle to keep the valve open but could be quickly pulled off when the DCT is full or if something went awry. It took about half an hour to put a gallon in (it took about 8 1/2 quarts total) so I could do other things while it was filling.

 

Thanks for the info and documentation. Very helpful as I plan to do this myself after my one freebie. I hate dealer service.

 

I'd recommend the Motive 2 gallon Power Fill.
Motive Power Fill

I can't recall if I added any additional parts, maybe longer hose. Works great and puts it in about as fast as you'd want for such a small hole. You pump it up to so many psi and then open up the valve. But not to fast at first. It will blow out of the filler hole. Try to keep your hand on that too when your first opening. You know you need three hands every time. It comes with a smaller metal tube with a hooked end. I believe you can source other angles also. I just been using the one it comes with. You just inset it in the filler hole with room for it to flow out when it gets to the line. There has been a couple times I've checked it by moving it around just to make sure it's not clogging it due to the angle in the hole. I just watch for when it gets around 8 quarts on my first check. I rig it up so it won't fall out even before I turn the valve. Three hands method. The bottle has quarts and liters measurements on the outside. Just holds a lot more. It's a great pump. Seals great and seems it will have a long life. I'll have to look to see what the highest psi is when using but it tells you. Just slowly open the valve all the way to open. Maybe this will help. Might save $10 on Amazon. After I'm done just clean it out with brake cleaner let it air dry and hang then store it. I've done about four times now. Just take your time.

 

Thanks for that nice write up and the procedures. I have saved them. The wires you refer to are inside the transmission - right? That's interesting. The manual does refer, frequently, to internal components that are connect to, or part of what is (are) apparently internal wiring harnesses. And there are one or more case pass-throughs for the wiring - I cant find an illustration of one, but you may have seen one while doing this job. Wherever they are, its another potential place for a leak.

 

Yes, they are inside the transmission a little forward of the filler hole center. I'm not sure it is wires or something else but is is plastic feeling (I think vertical) and can be moved with your pinky.

 

After filling isn't there a requirement to cycle through the gears and recheck the fill level?

 

@RKCRLR included the procedure for doing the Transmission Fluid Level and Condition Check, but interestingly, none of the other procedures actually call it out after the fluid has been added. The Transmission Fluid Fill Procedure calls it out as step 1, but that is before the fluid is drained. I would have expected it to be at the end after the fluid has been added.

 

Step 5/6 of the DCT Fluid Replacement Procedure invokes the Transmission Fluid Fill Procedure but you do have to ignore the part about draining the fluid.

 

I see. Sort of. Step 5/6 of the Fluid Replacement Procedure says fill to the proper level then calls the Transmission Fluid Fill procedure (which I would have thought was going to tell me how to fill it). But then step one of that procedure is check the fluid level - which assumes the fluid has already been put back in. And if it has, why are any of the the subsequent steps needed? Its a little squirrely. You ignore the steps about draining, then you see the steps to prepare for filling the transmission, then step 7 say fill it. After step 7 there is no call to check the level again. It does call the drain plug r and r step - but even that does not have level check after the fill.

 

Yep, you have to skip over steps and look for the applicable steps since they only refer you to the procedures, not the specific steps in the procedures.

Early in my career I was responsible for writing shop floor instructions for complex assemblies. It required integrating the requirements of drawings, specifications, health and safety, internal policies, etc. into something that could be followed step by step with each step individually bought off in order by a technician and/or inspector. I would never have gotten away with something like these procedures.

One could go through and cut and paste all the applicable information into a single procedure if they wanted. I thought I saw someone post that they did just that but I couldn't find it when I went to change my DCT fluid. And I'm too lazy to do it myself.

 

Does this include the extra two quarts that have to be added for tracking?

 

The 2 extra liters needed to be added for those cars that don't have the updated DCT which has a case and pan design change. Late 23 and on models have it. You'll need to verify which one you have to know if you need it or not.

 

Prior to a complete transmission fluid change, is it required per a GM procedure to do a back flush trough the filter? If it does, then I would need to get dealer to preform service for the required 3 yr. or 45,000-mile service requirement. If not, I will perform the task myself.
Any detailed GM procedure information would be greatly appreciated.
Thanks in advance for information.

 

The hydraulic system flush that's part of the external filter replacement procedure is not required for the DCT fluid change. Doing it yourself is easy and will save you lots of $$. Mine took 9 liters before the track fill. Rock auto has the DCT fluid for around $25.

 

Post 14 has your answer. But there is no transmission procedure called a "back flush" although that term does appear in the Service Manual in the context of a cooling system flush. We do not know exactly what the Hydraulic System Flush does. What we know about it is the name of the procedure, and we know that its purpose is to manipulate the valves with the goal of freeing any debris in the lines and valves and moving it to the filter before changing the filter. Whether or not it involves reversing the flow in the lines is unknown but if it did, would the dirt end up on the wrong side of the filter? It could be a rapid activation/deactivation of the valves, or operation at higher than normal operating pressure, operating the valves in a special sequence - we just don't know. Sometimes a "back flush" implies attaching of an external machine to force fluid in a backward direction - that's not the case here. Its all done with a computer while the engine is idling.

 

I'm a new owner of a 2020 with 9000 miles on it. I bought it three weeks ago and there was no service history in the GM system so I had the dealer do a oil/ filter and DCT filter service.

I'm contemplating if I want to do the DCT drain/ fill and future DCT filter and engine oil/ filter services myself. I have a decent jack and jack stands but would think it'd be much better to have two jacks to raise the rear evenly and while that may be fine for engine oil and filter the tilt would not be good for the DCT fill level.

I wouldn't mind having a quickjack but obviously it costs what a few services would cost at the dealer. But having one would make everything easy, well easier.

Opinions on using just the jacks?

Second, I don't have the E torx sockets. what sizes will I need for the shear plate or any other bolts or screws on the C8? Last, since I don't know what I don't know any thing else? I have the fittings, hose and funnel noted to buy, have a full set of sockets, torx drivers, etc...

 

The manual for my 2020 C8 calls for a fluid change after the earlier of 3 years and 45,000 miles. My car has 4300 miles. I called a dealer's service dept and they said it wasn't a big priority due to the car living in Arizona, where condensation in the case should not be an issue. They want $ 460.00 to change it. What do you think? My car has 10 months remaining on the factory warranty.

 

That is a great price for a DCT fluid change. While what the dealer says may make sense it doesn't override the 3 year requirement in the owner's manual. Which factory warranty are you referring to, the 3 year bumper to bumper warranty or the 5 year powertrain warranty? If the 3 year powertrain warranty then you should also have 10 months to get the fluid changed.

 

$470 for a DCT fluid flush doesn’t sound accurate. At dealership service department prices, that doesn’t cover the cost of the “12” quarts of fluid.

I suggest calling back and asking if that price is to flush the DCT fluid or change the DCT canister filter, or both. My guess is that it’s a filter change and not a DCT fluid flush.

I just thought of something…make sure they were looking at the C8 Corvette service pricing. $470 could also be a traditional transmission fluid flush cost.

 

I suppose you could do this with two jacks, but it's not the rear that you need to raise evenly, it's the whole car. You could use two jacks to raise the front and get it on stands then move the jacks to the rear and get that on stands.

Quickjacks are better, but if you're only lifting once in a blue moon then high-quality high-lift long saddle low-profile jacks and two quality sets of jack stands should suffice.

External Torx Plus 14 (EP14) socket for the rear cradle shear plate. A set of ratcheting wrenches works great for the fill plug. A regular set of 3/8" sockets and a 3/8" ratchet should get the job done for anything else.