vader86

It doesn't make sense to me that a fluid flush will fix a shudder problem. It only makes sense that it would alleviate symptoms and extend lifetime by removing the contaminated factory fluid, the problem that caused the shudder and the metal in the fluid is still there.

Has anyone looked at the fluid that was flushed out or the factory TC when it was pulled out of the transmission?

Luke42_02

I hear what you are saying Vader, but we have lots of reports of this working and no reports of it failing. Hard to argue with that.

vader86

Within a limited range of mileage, sure. Corvettes are not daily drivers for most people however.

How many have had the fluid flush alleviate the problem and then put another 50K miles on the transmission without a return of symptoms?

I suspect the flush only buys GM time by getting you out of warranty for the fix the engineers know should be done.

NSC5

The new fluid has different characteristics than the old and it can (and obviously does) help with shudder but my concerns are:
1. How much damage has already been done to the lockup clutch surface during V4 operation when it is being modulated to reduce vibration.
2. How much clutch degradation continues during V4 operation and how likely is the problem to show up again after 10-20K miles of operation?

The lockup clutch in the torque converter is a "wet" clutch and shudder occurs when the clutch is transitioning between an almost locked and fully locked state. There is no shudder at low speed or other conditions where the clutch is completely unlocked. Unless the clutch is in truly bad shape there will be no (or only a very brief and likely unnoticeable) shudder when it locks up in normal V8 mode. But in V4 mode it is constantly transitioning in and out of lock at very high speed and every time it goes into lock you pass through the almost locked to locked point and with clutch wear that is where shudder occurs because with wear (and the original fluid characteristics) it isn't smoothly transitioning into full lock and it has slight slippage at the point it should be fully locked but hasn't quite reached that state so it is jerking between locked and almost locked states.

The proper fluid can help provide a more sure engagement, those who have run a typical limited slip rear end without the proper friction modifier additive have experienced the same chatter/shudder from the wet clutch packs in the limited slip (aka positraction) rear. To me the jury is still out on whether this is a permanent solution or if it just temporarily masks the root problem of excessive clutch wear that occurs during the rapid modulation of the clutch during V4 mode. It is also interesting to me that the original fluid specs were developed in consideration of all of the multiple wet clutch packs used for ratio selection in the transmission. I have thought about changing my fluid to the new type but I am waiting to see what happens to others and whether the new fluid spec has any negative impact on the other friction components of the 8L90.

tobaccokid

Checking other forums the TC problemis are occurring with Cadillacs and Chevy Tahoe, Denali, and pickup trucks.

AWOL

The triple flush did not fix mine, had to get the torque converter changed

DAFFYDRUNK

This. You have people pronouncing it fixed that have put 3k on their car since it was done. I might start being a believer when I see 10k.

iclick

The first fix offered in 2015 was a full tranny swap--then they went to the flush-only, TC/flush, and back to flush-only around Feb. of 2017. As they were starting the TC-replacement/flush procedure Tadge said this in his monthly question-answer session about two years ago:

The service bulletin you cite says to perform a double oil flush if you suspect that the trans is exhibiting TCC (torque converter clutch) shudder. That procedure has been successful in fixing a few vehicles. This has primarily been a truck issue, pretty rare on Corvette. The bulletin is now being updated to have the converters replaced instead of just a flush since it has not been 100% effective.

What isn't clear is the type of fluid used back then, as it might have been different from the Mobil 1 (#19353429) used at least up until Feb. 2017 when I had mine done. I suspect the main reason for the change back to the flush-only method was that the bean counters at GM were having a conniption over the cost of the numerous TC-replacement/flush jobs that were being performed across the various GM car and truck lines. I'm skeptical it is a permanent fix, but time will tell. At least one here says it didn't fix his car but the swap/flush did.

For me the only valid cure for my two-year A8 ordeal was to buy a new car with an M7. Life is good now.

tcinla

Wait... you have to PAY for the triple flush ???!!!?!?!?!?

9157

My '16 Z51 had 41k miles when the triple flush was done last week. The old fluid was dark and there was no materials attached to the magnets. The tech said the old fluid looked surprisingly good. He said that the A6 fluid with similar miles would be black in a normal transmission.
so far the triple flush has cured the RPM fluctuations at highway speeds. The shudder has also been reduced but still is clunky at times. I now only use paddles and the shifts are much quicker than before. I was very skeptical about the triple flush but it definitely has improved my situation.

DAFFYDRUNK

His car is a salvage car that he rebuilt, so no warranty unfortunately.

onyx_z71

While I hope the flush helps alleviate the issue, I'm skeptical. It seems to be the equivalent of mashing up a couple bananas and pouring them into your crankcase to stop a rod knock.

If the transmission was developed to work properly with the original fluid the car came with, I fail to see how a magical fluid swap will fix it long term. Personally, I think it's an issue with the pump.

I read somewhere that the 8L90 has both a high pressure pump and a low pressure pump. Supposedly, the transmission only runs off the low pressure pump during light loads in order to increase efficiency and mpg while it operates at higher pressures only when needed. I wonder if the low pressure mode during light cruising is insufficient at keeping the converter locked because it makes sense that the issue doesn't happen while paddle shifting because I would think the full pressure pump would still be operating due to the V4 mode being inactive while in paddle shift.

If the problem lies in the pump, running the transmission at full pump pressure all the time to correctly solve it (if it actually would) may alter fuel economy. That could mean GM may not be able to use that as a solution due to EPA/CAFE rules and we end up with a special fluid that could have some sort of friction modifier additive to limp the car along as a Band-Aid.

Just my wild theory.

Luke42_02

Update: Ok, I feel like the triple flush worked... sort of. I still feel a vibration, it's faint, but I think it's still there. Previously it was faint at times and very noticeable at others. The RPM variation is gone, even in V4 mode.

I think I will consider it "fixed" until something bad happens and use the range AFM.

bbcb

Triple flush is just more bull.... first car I have owned since high school that I even heard the tranny being mentioned..cars today should be having tranny problems period ! best part ..GM is not too concerned ...and as I have stated..how come GM cust. service has stopped responding on this forum .....mmmm

tail_lights

Just had mine flushed. 2015 Z06 with 20k miles. Originally told it needed a converter but according to the dealer GM 'downgraded' me to a flush (hopefully the triple). After I go pick it up I have an immediate 3k mile road trip so I will tell rather quickly if the flush made any difference. I'll post my findings!

iclick

You see them pipe in occasionally for big problems like a poorly fitting console lid or missing tire valve cap, but they're MIA on A8 threads. Too rough in there, I guess.

As for tranny problems in general, I skipped the 2014 MY because it was a first-year model, but never gave a second thought to the A8 being a first-year tranny. After all, GM has been making slushboxes since 1939, so you'd think they'd have it down by now, or at least have it down enough where early problems would be diagnosed and fixed forthrightly. Three years later we're still seeing problems crop up.

tail_lights

Flush did not work...... Not even close. May have made things worse, honestly. Wasn't even out of Houston yet and knew that it wasn't having the desired effect. Made for a crappy road trip (at least while on the road) Dropped it off as soon as I got back and now maybe I'll get the converter changed.....

tcinla

I thought the flush was for the differential to deal with the ring/pinion issue. No ?

Crossed Flags Fan

Anyone know the latest A/T fluid part number. Lots of confusion as to the most recent one.

ddelallata

It's Mobil1 LV ATF HP fluid.
GM part number: 19353429