Gearhead Jim

Our 2017 Z51 A8 was built in September 2016.

The Owner Manual lists the transmission fluid as "Dexron-HP Automatic Transmission Fluid" #19331925.

The latest version of Bulletin #16-NA-175 dated Dec 1, 2017 for Shake/Shudder says that after dropping the trans pan and blowing out the cooler lines (no more triple flush), refill with "Mobil 1 Synthetic LV ATF Dexron HP" fluid.

1. Are these the same fluid or different?
2. Is the Mobil 1 fluid now the factory fill? The 2019 Owner Manual shows the same fluid as our 2017 Manual, no mention of Mobil.
3. Which fluid would have come in our car from the factory?

Thanks!

NSC5

Jim,
It was well into calendar year 2017 when the latest friction modified fluid was approved for addressing the 8L90/8L45 shudder issues so unless your vehicle has already been into the dealer for shudder it still has the factory original older fluid.

The new fluid is compatible with the older fluid but the pan is dropped and the lines and cooler are blown out to get as much of the old fluid AND the wear material out as possible.

GM, like most manufacturers, does a lousy job of updating their manuals during a model run. When I bought my 2001 GMC Sierra, which was the first year of the new Isuzu/GM joint venture Duramax diesel, the supplemental manual for the diesel engine contained material copied from the supplement for the older and entirely different Detroit Diesel designed 6.5L engine and was not at all relevant to the new engine. Unfortunately a lot of the dealer service shops don't keep up with changes very well either.

Flame Red

Jim,

I'm interested in trying to change the fluid on my '15 as I am starting to see the shutter at times but I know it would not do it for a dealer if I took it in. I searched through the infamous A8 sticky at the top of the forum and found this 2018 post:

https://www.thelubricantstore.com/mo...-case-6-quarts

Looks like it is about $11/quart. I am not exactly sure how many quarts would be needed so I'm subscribing to this thread and hopefully someone will chime in with that.

I HATE doing tranny fluid changes. It is a super messy job and usually I end up taking a bath in it! Last one I had a forum member do it for me on my C6 since he had a full lift. I would be tempted to install the LMR tranny pan but I know GM will use that as an excuse to void my power train warranty and extended warranty but I don't mind yanking the pan and replacing the gasket with a stock one.

Another thought I had - and I WILL get flamed for this - is going to a Jiffy Lube and provide them the fluid and they would put it through their fluid exchange machine. I have done that with MANY other cars and it worked out well, but I know that would be poo-pooed here.

And some other useful information:

NSC5

I have changed transmission fluid on a lot of vehicles and for my pickups I also change to the regular Allison deep pan instead of the shallow pan that goes on GM trucks. But for the Corvette you are better off going to the dealer for this service:

1. Given the design of the Corvette neither dropping the pan nor filling is nearly as simple as it is with most vehicles.
2. You really need to flush the lines to get the old stuff out.
3. Anything you do yourself with this issue may invite more trouble if you have to take it to the dealer later. You probably have the earlier revision torque converter so for your vehicle the dealer likely needs to change it out also.

I do most of my own service work and I recently changed the fluid, pan, and both transmission filters for my 2018 GMC pickup along with changing the rear differential fluid and greasing the chassis (HD pickups still have grease fittings for the suspension components). This was a very easy task compared to what is needed to deal with the Corvette transmission fluid.

If it weren't necessary to replace the filter in the pan then you could use the method many of used originally in the GM heavy duty pickups to switch from Dexron to the proper Allison synthetic transmission fluid. You disconnect the lines at the cooler, immerse the return line in a container filled with the proper fluid and put the out line into an empty bucket and run the vehicle and let it pump the new fluid through the system. That required two people because you want to make sure the return line always had fluid but it was a simple and easy method for just upgrading the fluid but the 8L90 procedure is to address a problem and not just upgrade the fluid.

This method is far safer for the transmission than an improperly operated power flush machine and I wouldn't trust Jiffy Lube or similar. I had one direct and one indirect experience with Jiffy Lube. In 1989 I was running out of town for a family emergency and took my 1985 Monte Carlo SS for a quick oil change before the trip since I didn't have time/energy to to it myself. The oil change went fine but they came back telling me the differential fluid needed changing and they had a sample to show me. This had two problems because I had changed the fluid a month earlier and I knew it was clean PLUS there was no drain port on those GM differentials and to change the fluid you removed the shell to get the fluid out. The "tech" quickly melted under questioning and admitted that the fluid wasn't from my car but just a sample of how it might look. In 1990 I bought my first pickup and when I was picking it up from the GMC dealer they were replacing the engine in a brand new pickup. The shop manager explained that the customer took it to Jiffy Lube and the kid who started the engine to check for leaks didn't wait until the other kid had put oil back in it. Not surprisingly there weren't any oil leaks during that test

olblue75

Where do you find the LMR Trans Pan???

Flame Red

Sorry - my mistake - was not LMR. LG MS. https://www.lgmotorsports.com/lg-motorsports-c7-corvette-aluminum-high-capacity-8-speed-trans-pan.html

I think there are others out there now too.

Gearhead Jim

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GM does indeed do a crummy job of updating their information. Starting for MY 2009, the C6 got a different (better) differential fluid. Our 2009 came with that new fluid but the Owner Manual still listed the old stuff. And eight years later, the GM website that the dealers use still had incorrect information for our 2009.

Flame Red-
I would find a dealer you can trust (ask for recommendations here if needed), take it to them and explain the problem. Call the parts department in advance to verify that they have the Mobil 1 fluid in stock or locally available. Print two copies of that bulletin (be sure to get the December 2017 version), give one to the service writer and leave the other in the car for the tech. Make it clear to them that you want the drain/blowout/refill performed even if GM won't pay for it. Hold your breath when they tell you the price. But you will have preserved your warranty, your garage floor, and your sanity.

From the replies above, it sounds like the Mobil 1 fluid is still not the factory fill and is indeed different from the normal GM fluid. Correct?

olblue75

Thats a nice pan but 800 bucks I'd have to see some testing and data on these. An yes Katech makes one but they want a cool grand for theirs!! I sent a email to Derale who makes steel pans with cooling tubes to see if they can do something.

Gearhead Jim

Getting back to the original subject;
Is the Mobil 1 fluid now factory fill for the A8 cars, or only an "install if needed" replacement?

olblue75

Said they dont offer a pan for our A8 application suggested contacting Ecklers.

Flame Red

Still thinking of trying the A8 fluid switch myself. Page 55 on the doc has a lot of good info.

http://www.atra.com/Webinars/GM/8L90_Introduction.pdf

I have one of those Mityvac fluid extractors that work off a compressor and can hold more than two gallons. It can measure exactly what it sucks out and I can replace the exact amount without opening the pan. Six quarts of the new fluid is slightly over $70 delivered. Two cases should be enough for a triple flush.

obxchartercaptain

I just had mine flushed and blown out Friday....they said they uesd OEM fluid with an ADDITIVE....My shudder is gone....told me to drive it for another 300 miles and see if it comes back...if it does they will change the TC....

joemessman

They install it at the factory now. They started doing that at sometime during the production of the 2017 model year builds. This is a good estimate as to when. Right after the TSB which would be January, or February 2017.

Flame Red

What is this additive people keep mentioning? I see is a quite a few posts that talk about it. Anyone have a TSB? Part number? Should be listed on the dealer service order.

rmorin1249

Gearhead Jim

I have not heard of any additive in the sense of something that you pour into the tranny along with the ATF. The Mobil 1 ATF may have some additional ingredients added at the factory that people would call additives.
Or maybe I'm missing something...