[ctrlz]

Originally Posted by EMTNLSS

I'd say shudder is mostly fixed now. Probably not all the way just because there's still some old fluid in there.

The shudder is not a property of the fluid. It is the result of uneven wear on the clutch plates. Once they are partially worn, and you replace the fluid, the hope is that they start to wear normally again and the bumpy bits even out. Let it go too long, and you can't reverse the process.

Normal transmission fluid has friction modifiers allowing the clutch plates to engage smoothly and then lock. The defective fluid is hygroscopic. The presence of small amounts of water interferes with the engagement of the plates, resulting in a slide-grab-slide-grab type of engagement. It's like putting a bit of dish soap on a slip-and-slide vs. just plain water.

[argus]

Just ran across this thread after getting a transmission fluid flush done on the Camaro this week at 45K miles. No shudder before or after, and wasn't even aware of a TSB until I saw this thread. Granted, I had essentially the same 6.2L and 8 speed in my '15 Sierra 1500, and it was plagued with transmission issues, so much so that I traded it in.

Anyway, I took the Camaro to a dealership I trust and have used for years, same service advisor. As noted earlier in this thread, it's a procedure where they flush using 20 quarts of Dexron HP. Drives as fine as ever now.

BTW I don't mind turning my own wrench, and did so for decades, never having any trust in dealerships. That can change as you get on in years though and time becomes more precious than dollars!

[PBB66]

Hmm. Yeah I understood it was uneven wear. So you are saying the culprit is the original ATF that Chevy used with the 8L90? And that replacing with the blue Mobil 1 as recommended is the hoped-for solution as, not being hygroscopic, it will potentially allow the clutch plates to start wearing more evenly, reducing deterioration and buildup of shavings in the fluid?


That re-tuning the transmission is not entirely necessary?

Originally Posted by ctrlz

The shudder is not a property of the fluid. It is the result of uneven wear on the clutch plates. Once they are partially worn, and you replace the fluid, the hope is that they start to wear normally again and the bumpy bits even out. Let it go too long, and you can't reverse the process.

Normal transmission fluid has friction modifiers allowing the clutch plates to engage smoothly and then lock. The defective fluid is hygroscopic. The presence of small amounts of water interferes with the engagement of the plates, resulting in a slide-grab-slide-grab type of engagement. It's like putting a bit of dish soap on a slip-and-slide vs. just plain water.

[haggler]

Generally speaking you want to ATF fluid change at ambient temperature because the replacement fluid is at ambient temps. ATF expands with heat.
I don't know about this transmission because I have a manual, but on my other vehicles I've done a cooler line exchange which pretty much changes all the fluid. The dealer will do this with a machine that pumps in the new fluid. The jist of the DIY version is you drain and service the pan fluid, filter, and refill - then start the vehicle and capture the fluid as it exits the cooler and is heading back into the pan. You can disconnect this line and use a hose to redirect it into a quart marked jug. The challenge with this process is you need to be able to add fluid at the same rate as it is being captured from the cooler return line. I'm not sure this transmission has a fill port in the engine bay. Doing this though, the old fluid never mixes with the new fluid and you then top off and do the normal level check procedure.

[ctrlz]

Originally Posted by PBB66

Hmm. Yeah I understood it was uneven wear. So you are saying the culprit is the original ATF that Chevy used with the 8L90? And that replacing with the blue Mobil 1 as recommended is the hoped-for solution as, not being hygroscopic, it will potentially allow the clutch plates to start wearing more evenly, reducing deterioration and buildup of shavings in the fluid?


That re-tuning the transmission is not entirely necessary?

Re-tuning not necessary. The fluid change is intended to remove the accumulated water which has, in a way, become part of the ATF. With lubricants, you always hope for the ole "water and oil don't mix" business to keep you out of trouble. But a hygroscopic lubricant actually attracts water, and even small amounts can drastically degrade the fluid. All the chemical engineering intended to make things slip and slide off the parts and each other goes out the window.

[truckrglenn]

There is a section on this site pertain to transmissions.