Has anyone requested that a dealer perform the subject flush without the filter and/or fluid replacement? What did they charge and how long did it take?
I am considering having the dealer perform the flush prior to my replacing the filter and fluid. Should only take a 1/2 hour or so, right?

 

I asked my dealer about it and they said they would do the hydraulic system flush and that it wouldn't take long but I didn't ask for a quote. My main concern is if I would be doing more harm than good on the drive home. There is some precedent in the service procedures for performing a HSF without changing the filter and at least one person has reported that had the dealer do the HSF and then changed the filter themself. And while the procedure doesn't say you can't drive after performing the HSF without changing the filter it doesn't say you can either.

I wish GM would come out with a position on this. It would be a viable option for those that would like to do the DCT filter change themselves but don't have the equipment to perform the HSF. There is also a leak check procedure after the filter change that requires a MDI2 tool but I imagine that a quick drive around the block and then check for leaks would accomplish the same thing.

 

I doubt this adds any clarity - but the HSF procedure, as has been pointed out a few times, includes a statement about not performing it unless it is called by another procedure. One of the procedures that calls it is the DCT external canister filter replacement procedure, where it is always followed by a filter replacement. In other words, it is never meant to be performed as a standalone procedure, but always in the context of another procedure. And yes there was a bulletin with a procedure that called it, that was not followed by a filter replacement. It is attached. Prior to step 1, it says "Prior to performing procedure, verify the vehicle mileage is under 12,000 km (7500 miles) or that Dual Clutch Transmission Canister filter maintenance has been performed. See maintenance schedule for the Dual Clutch Transmission Canister filter. If necessary, filter must be changed prior to this procedure." However, at the end of the procedure, step 9 calls for performing the HSF, and it is not followed by another filter change. It is my guess that its fine to perform it, then drive home and change the filter - but I doubt we will ever get any clarity on that unless one of the GM reps comments on that during a public forum.

 

I can't imagine there would be any issue driving the car home after a HSF. If it's meant to move garbage from the solenoids and other areas to the DCT external filter, then the garbage is in the filter and no where else. In theory. And these DCTs are capable of going 22.5K miles on a filter. In theory..... which I don't personally subscribe to.

 

I've noted a few times, the Maseratti MC20 which uses the same Tremec 8 speed DCT calls for that filter to be replaced once a year, or every 9320 miles.

 

Yes, I've seen that info posted by you Andy and it's very much appreciated. Based on the risk reward (potential at least) I don't know why one wouldn't change the DCT filter every other oil change (assuming only one per year). Even without an HSF I think it'll help. And certainly every three years when a full fluid change is done. That's my plan as I intend to keep the car for a while.

 

The flush is done to clean (flush) all contaminants and clutch debris to collect in the filter which loads it up with that crap so the last thing I would ever do is have the flush procedure done without then changing the filter. Talk about introducing a transmission problem!

 

I am still not convinced about the contaminant and filter theory of DCT failures. Some cars get it within a few hundred miles after leaving the dealer lot, others have gotten it years later after having their DCT filter and/or filter serviced.
Back to the OP question though, if this flush is meant to move particles along the hydraulics so that they can be caught by the filter, that's what 'I' would expect to happen. If course, I am not a transmission engineer, I am just using common sense.

 

Perhaps not all of them. But some forum members have reported that they had a transmission issues there were solved by the HSF procedure. This suggest to me that least some of issues were a result of debris in the valves or lines that was removed by the HSF. If what you mean is you are not convinced that the filter is doing it job, resulting in contaminants getting past it, that is a possible explanation. You've probably read the theories - the filter is too small, or it bypasses when cold. Or there is an unfiltered path. Sound odd? I do not know how the lines are routed in the C8 DCT, but I found an example of another DCT that has some lines that do not through the filter - it proves nothing - but shows that the possibility is not that crazy. No more crazy than making the filter inadequate to do its job anyway.

 

Care to share the data behind that statement or is it an opinion not based on data?

 

Some have failed early, almost immediately really, others 2-3 years later.

 

But why would some fail really early and others much later? Maybe there's more than one mode of failure and the codes emitted by the computer cannot distinguish between the different modes. To the computer it may all look like clogged solenoids.

 

I agree that some (many?) of the failures may be unrelated to contamination, especially the ones after the first filter change. The error code from a sticking, leaking, or misbehaving valve unrelated to contamination may look the same as a problem related to contamination.

What I'd like to see (but probably never will see the data) is if there is a correlation with failures that happen after the first DCT filter change between the ones that had the hydraulic system flush and those that didn't.

 

I know. I said some (early and later failures) are corrected by the HSF, which seems to say at least some are caused by contamination. I never said (and I don't think anyone ever said) that they are all caused by contamination of the valves - if that is what you are getting at. Based on memory, there have been failures of internal sensors, of internal harness components, mechanical parts like the parking pawl, probably more. Sometimes after an HSF, it was solved by replacing a valve body. Was it clogged? A valve could fail without being clogged, The solenoid that actuates a valve could fail, which would have nothing to do with contamination. We typically never find out what failed when a transmission is replaced. Honestly, when you said you were not convinced by the "contaminant and filter theory." I was just not sure what you meant. Sound like you meant a theory that all problems were due to contamination or filter failure. I don't think so either.

 

You are also right that the codes do not (ever) indicate the cause of the failure. Codes indicate an issue - like a pressure inconsistency - or transmission creep mode is disabled - etc. They never say a valve is contaminated, replace it. Every code leads to diagnostic procedure, that does things like perform an HSF to see if that fixes it, or topping off the fluid, or draining the transmission cleaning the pan, refilling it. Or replacing a valve body. Or checking a wiring harness or connector or circuit. Sometimes when none of the suggested remedies fix it, the final step is transmission replacement. So, I don't think anyone should ever conclude it was contamination based on the code - but one might do that if the HSF solved the problem.

 

If GM knew why some failed early and others fail much later they would have addressed it. Certainly no one on this forum would know anymore. Although it does stimulate conversation 👍

 

Interesting. Does Maserati need a hydraulic system flush operation before filter change?

Aside: It gives me absolutely zero comfort that Maserati uses the same DCT. They have a history of terrible transmission issues. Any part association with that brand is unnerving 😂😂😂😂.

 

I do not know if they use the HSF. Its a software controlled manipulation of the transmission. Who supplies the software? I just thought the differences in the maintenance schedules is interesting. And the MC20 also calls for fluid replacement I think at 4 years or 4 times 9320 miles including replacement of the internal suction filter.

 

A similar situation to your question. I have abt 2100 mi on my 23 HTC SR, purchased in Sept 23. I only have these miles due to running it up for break in. I will likely only keep this car another year or two tops for abt another 1000 miles. Due to all the screwy fluid mileage/timing change requirements, I recently opted to use the "free service" for my first oil change. Since I am abt to track it, I also requested that they change the DCT fluid while doing the free svc. (I know its overkill, but I want no excuses once I start tracking. I have ready access to a track).

In any case, the additional DCT fluid was on me. The dealer agreed to one hr of incremental labor and 10 qts of the pricey fluid (assuming 11 total and GM buys 1 qt for the free svc). Seemed reasonable. They get $270/hr corvette shop rate ($220, all else) and the fluid was $46/qt (dizzying figures, but seem to be consistent with numbers reported by others). Out the door, incl taxes/fees was $780. FWIW HTH