Yes, I was thinking along the same lines (the bolded text). During testing, if they looked across more than one vehicle, they probably determined that the some filters filled more quickly than others. And, either by testing or some sort of calculation/extrapolation, they determined that by 7,500 miles, some very high percentage of vehicles would not have a full filter. In my opinion, 99% would be too low - because it would mean 1 out of 100 might overload. A threshold more like 99.99% (1 in 10000) would be better. And, thats pretty hard to test - it would require then to test a whole lot of different cars. So, they either just added a margin in terms of miles, - or the calculated it. That's a long way of saying that, if the theory is true, most cars will not clog up and bypass, but some outliers might.

 

You pretty much replicated what I have done with my 2023 Z06.

I did my DCT filter changes at 565, 2365, 3919, 5018, 6409, 7821 and 9410. I cut every filter open for inspection and performed the hydraulic system flush twice at 6409 and 7821 miles by first removing the in service filter and using a new, clean filter for the flush which I then removed and cut open. I changed the fluid twice at 2365 and 7821 miles. I sent a sample of the used fluid at 2365 miles for analysis.

My findings pretty much parallel yours. I have yet to cut open the filter from my last change, but externally it appears to be relatively clean.

The two filters I cut open after doing the hydraulic system flush - using the same GM MDI2 diagnostic interface used at the dealership level showed almost zero debris or contamination trapped in the filter media.

Thanks for sharing your data.

 

If the problem was a marginal filter design allowing it to prematurely go into bypass mode during break-in then you would expect the problems to be clustered prior to the filter change but this isn't the case. Many DCT problems have occured with very low miles (there was one post recently with 8 miles). And once you got past the 7500 mile filter change then the problems would go away if due to excessive contamination during break-in. While most of the reported problems appear to be infant mortality there are still some that happen later on, some not long after a filter change.

The data just doesn't support that the problem is the filter being overwhelmed and going into bypass mode.

 

Good point. And, while I am not necessarily agreeing with the bypass theory, your point assumes, I think, that the shedding of debris is smoothly declining throughout the break in period, so that the filter is not near full (or at its capacity target) until near the end of the period. The data in this thread is consistent with a smoothly declining rate of shedding. But what if the "outliers" were suffering from unexpected "clumpy" debris shedding? We need a look at filters from cars that had an early failure. We never get that because those generally depart with the replaced transmission. GM and Tremec probably look at them. There was campaign to return filters to GM for analysis, but those were filters from the normal changes, not a failed transmission.

Another theory, not in this thread, and not suggested by me, is that the filter bypasses at times even though its not full. Since bypass requires a differential pressure across the filter, it would seem like there would have to be some sort of pressure surge - at the input to the filter. Or a sudden loss of pressure in the downstream side of the filter. There must be some sort of pressure regulation in the fluid pump. And downstream from the filter, its valves that regulate the pressure to the transmission components. But we have very little information on the plumbing - only a list of valves and what they do.

 

Yes, in theory there could be an outlying problem of excess contamination being generated and causing the filter to prematurely enter bypass mode.

But, to begin with, DCT failures are outliers. A majority of DCTs don't have any problems. And, of the DCTs that have problems, many of them are leaks, park sensor drift, software, etc. and known not to be contamination related. So if you think you are one of the unlucky ones that are going to have a problem that could be due to the filter being prematurely loaded then you could follow a more rigorous filter change schedule.

But if you happen to have one of the cars that is causing excess contamination and you prevented initial contamination related problems by frequent filter changing are you just postponing the problem? I.e., where is the excess contamination coming from and is the root problem just going to cause problems later on?

 

I also doubt the filter is going to bypass. GM asked for filters back on 2020 from Techs. IF they found significant issues, IMO they would have decreased the 1st filter change miles. The did not.

My observation, with my 2020 C8 (also mentioned by some others) was I had a somewhat jerky movement when going very slow. That is what I observed as I crawled into the garage watching the gap from driver's mirror tip (not folded) to garage door wood molding and door weather seal. As I do now with the E-Ray, kept it to about an inch so the harder to judge passenger door mirror tip easily clears. That somewhat jerky movement stopped once I passed ~1000 miles. I attributed that to the 1st gear clutch plates wearing off high spots.

In 2020 and 2021 a number of posts where folks got early, with relatively few miles DCT CELs. Dealer tech relayed the CEL number to GM Tech and were told perform a Flush. No new filter or any added or changed fluid JUST a flush. In most cases CEL was gone and it was reported did not come back in many cases.

Was one reason I took advantage of the GM FREE offer for engine Oil/Filter change and DCT Filter (with FLUSH) end year one with ~3000 miles.

Jump forward to my one 2024 E-Ray experience. Had zero jumpy movement driving into my garage with my E-Ray. AND because of the wider rear fender, since I must make a "K" turn into the garage from the driveway, am not perfectly perpendicular so even more careful. Go slower and back-up on occasion to achieve that ~1 inch gap. Rear fender gets close to the white, house paint ~3/4 inch garage door rubber weather molding. ( BTW, that white house paint comes off easy from the rear fender- ask how I know!) There was no jerky movement from day one. Perhaps they changed the clutch material or have the clutch plates supplied super smooth! See Sidebar.

I also don't see that many early, few miles DCT CELs in the past 2 years. Some, but subjectively not nearly as many. In fact will have my year one maintenance done end month. I'll have about 4500 miles compared to ~3000 with my 2020 C8 (now with AWD, driving in rain, I avoided with the 2020 and took the wife's SUV.) Like all my 7 Vettes it's my DD and now the wife reminds me I say it's so good even in heavy rain, which it is, why not take the Vette and GET IT DIRTY! No choice! So I'll have the engine Oil/Filter changed and use my many GM Points. So around end next year I should have ~8000 miles so will have the DCT Filter changed and my Engine Oil/Filter on GM's dime.

SIDEBAR
Just watched a video of an NHRA ProStock 3 disk clutch BEING SERVICED AFTER A RUN. The Tech used a diamond tipped tool in what looked like and old record player type machine making the disks super smooth. They do that after every run for consistent very quick Lunches.

Just checked the year, and in 1992 soon after Kenny Bernstein broke the 300 mph record I was at the NHRA National event in Charlotte. Was probably a Friday as that is when I like to go. I saw Dale Armstrong (Bernstein's Chef Chief) near the fence, no one around and he was machining their multidisc clutch plates. I asked what he was doing and he said these are new disks but I like to machine them to a more consistent thickness and surface! Wasn't taking off much BUT lots of carbon dust in the air!

 

I agree, I don’t think the filter design or size is the problem. I had the filter replaced on my ‘21 C8 at 4000 miles and again at 7500 miles. The transmission fluid was replaced shortly before 3 years of ownership at just over 10,000 miles. My transmission required a valve body replacement at 13,000 miles when it set an internal P2856 code - Clutch 'B' Pressure Charge Performance.

 

Yup. That code comes from "transmission fluid pressure sensor 2", which is located in the" Main Valve Body". Is that the one that was replaced? That sensor measures the transmission fluid pressure to the "even clutch", which is for gears 2,4,6, and 8. The specific code appears to indicate an overpressure condition that lasted more than 1 second. It says that actions taken include disabling the even clutch (so gears 2,4,6 and 8) would be unavailable, and also display the "Idle Creep Disabled" message. Did you get that message?

The above info is from the 2020 version of the manual, and some (many?) transmission procedures have been updated. But in the version I have, replacement of the Main Valve Body is not one of the suggested remedies. The remedial steps include checking fluid level, Even Gear Clutch Hydraulic Control System Cleaning Procedure (this may have been replaced with the Hydraulic System Flush procedure), replacement of the DCT external canister filter, removal of the pan and replacement of the internal filter. If none of that fixes it, it jumps to transmission replacement. So, replacement of the valve body must have been added in later updates. Thats a good thing, I think.

 

Yep, lost the even gears coming to a stop light getting off the freeway. The car jerked hard as it slowed down and I noticed it skipping the even gears on the DIC. I had the transmission in manual mode and switched back to D. The car appeared to shift normally from that point on. No check engine light was ever set and no messages appeared. The only way I knew it was transmission-related was it skipping the even gears. A few days later I hooked up a code reader to check if any internal codes had been set and that's when I discovered P2856. The dealer diagnosed it and said the main valve body needed to be replaced. Twelve days later I got my C8 back.