cdurkin1259

Just posting this as an FYI. Had an “Idle Creep” alert at 38,000 miles on my 2021 C8. Took it in and they couldn’t find an issue and just flushed the trans fluid. At 45,000, got the idle creep again and they are replacing the valve body on the transmission. I got 15,000 miles left under warranty so suffice to say if it happens again and they don’t replace the transmission, I’ll trade it in for ?

undecided1965

Very disheartening that this is happening on higher mileage cars as it has been touted as a fail caused by early mileage break-in debris. Yours must be one of the highest mileage C8 vettes out there. The good thing is that you have the issue documented. Other brands (BMW) will do good will repairs past the factory warranty expiration if the problem was flagged and documented by the dealer before the expiry.

dohabandit

A bike... At least bikes are easy to work on and relatively easy to fix.

dohabandit

If I had to hazard a guess, having a wet clutch running in the same oil bath as the dozens of solenoids and valves is a bad idea.

Might have been better to isolate the clutch fluid from the rest of the transmission. The one item that for SURE wears and releases particulate matter is the clutch, throughout the life of the car. No matter what you do, clutches gonna clutch...Treating the circulating oil like a slushbox maybe a bad idea?
I know some people say they "pampered" their cars during break-in and still had issues with solenoids too, but I would be willing to bet there might have been a few "white lies" there. It's a performance sports car. People didn't buy it to drive it like a granny.
Problem is this means you need another pump and coolant loop, unless you could use some sort of internal heat exchanger.

I haven't seen a single "technical document" that discuss what exact material is fouling these valve bodies. GM is keeping us in the dark.

RKCRLR

But how does the clutch material get around the filters and to the valves? Is the filtration design inadequate and allowing unfiltered fluid to the valves? Filters bypassing prematurely? Filter media allowing too much contamination through? And keep in mind that slushboxes also have clutches.

dohabandit

Ohh, I am aware! I hate to admit it, but I have a slush box "tranny ****" addiction problem.
Be careful, but if you watch the "Precision Transmission" channel on youtube, you might learn all the nuances of every auto transmission ever made.

Difference is in slush box you have a lot more surface area / clutch area, and the fluid flow may be different where 100% is filtered before returning to the valve body. Those internal clutch plates are also downstream of the torque converter.
I would be willing to bet the clutch pack in the DCT works harder and I am not sure about how the fluid flows. They do have TWO filters though. One in the pan and one external cannister filter.

Avanti

Hardly "high mileage" for a daily driver, even if it is a Vette. Sorry to hear about your issue, btw.

newcastlegreg

Porsche PDK has separate oil bath for the clutch….DCT has to much stuff in one oil case…

Mitchell_B

Is that a fact? Makes much more sense to isolate the clutch pack lubrication which will absorb shed clutch material for the life of the unit.

dohabandit

https://go4trans.com/technical-trans...-transmission/
The "downsides" listed in the above article appear to sound familiar.

https://www.planet-9.com/threads/diy...l-mode.237865/
A view of the clutch cooler, and gear cooler on the PDK.

To be honest, I think combining the two into one oil bath was a bad idea. Maybe done due to cost?
Or was it done to avoid a patent infringement? Who knows...

Mitchell_B

The fact that the Germans built their trans indicates different thinking from Tremec.

Innovated

So is it looking like an increased amount of fluid drain and fills, along with additional flushes and additional filter changes beyond GM's recommended service intervals is something that should be considered ?

Mitchell_B

That’s how I look at it. It certainly seems reasonable to at least change the external filter every engine oil change. It’s simple enough, you won’t hurt anything and it could help avoid a large maintenance issue.

Innovated

From the PDK link someone posted above :

"Keeping good oil in this system is critical. Poor oil will degrade valve body operation, wear the valve body bores and seals, and degrade clutch engagement. If the valve body isn’t operating correctly, everything downstream will deteriorate. Also the fluid is full of additives such as anti-shudder compounds that are essential to smooth operation."

Mitchell_B

And I would change the fluids and filter/ external filter before the recommended 7500 miles. How much sooner depends on how your car is used.

I would rather spend a relatively small amount up front to decrease the odds of having a much more expensive issue later on.

Vetteman Jack

Sucks that you are having problems with the transmission - especially since you supposedly had the problem fixed 7K miles ago. Hopefully with this repair the problem will not happen again, but if it does, and you decide to go for a different car, perrhaps a Caddy Blackwing would be a good choice.

cdurkin1259

Thx but I actually work out of my house and that mileage is just taking a drive every day it’s sunny.

dohabandit

I changed my DCT cannister filter at 1750 and 7500 miles. I will probably change it again at 14k miles. Now that I am tracking (not a lot yet, but planning a trip to Sebring), I am considering changing the internal filter when I drain and replace ALL the DCTF.
If tracking it is a requirement to replace all fluid after X track hours (24 right?). I think it might be warranted to replace the pan filter too. When I do that, I will likely replace the pan with a Dodson pan cover.