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Okay, devils advocate here for a minute. But first, sorry you are dealing with this and hope it gets resolved.
Garage changes your diff oil with either correct or slightly incorrect oil. You drove 1000 miles. Unless you were dumping the clutch with sticky tires, I don't care if there was 3 in 1 oil the diff would not be garbage. Here is why I am saying poop happens. My Chevy Avalanche was taken very good care of. I did all PROPER fluid changes myself. Never a burn out or mistreated. The diff took a poop. When I took it to the mechanic he told me it did not matter what I did, the a bad bearing destroyed the diff. Out of my control. Never beat on the car. Never put in the wrong fluid. Never peeled out. The bearing failed and my diff was trash. So I ask, when the dealership said the diff was trash, what was trashed because of the "wrong" fluid.
I agree with those who recommended you politely and respectfully state your position to the manager (or higher), provide documents that support your position, and request reimbursement. Make sure to document everything you do. If that fails, perhaps telling the local news media about the situation and ask them to do a story on it. That kind of pressure might bring about a resolution. If that fails, hiring an attorney may be inevitable.
I would pin the dealership down on exactly what part(s) failed and why. Is the type of fluid really that critical? How does the dealership know the fluid caused the failure- is it possibly a coincidence that a part failed after the wrong fluid was put in, but it was destined to fail anyway? I don’t know anything about Corvette diffs but I have a lot of experience with courts & lawyers. (No, I’m not a bad guy) I’m just thinking out loud about issues the grease monkey lawyer might raise. His best “defense” will likely be claiming they did nothing that would cause damage, thus forcing you to prove they did.
It’s hard to grasp that 75W140 gear oil would “trash” a diff in only 1000 miles, especially without track use. Keep in mind that Bowling Green had a long run of under-filled C7 diffs, some worse than others. Even though GM has never admitted the problem, It is possible that you had a semi-damaged diff (under-filled) without rear-end noise. Then, when Grease Monkey replaced the gear oil with the thicker stuff, it pushed the diff all the way over the edge and you heard the noise, all the more attenuated because of the thick oil. Just my .02
75W-140 didn't cause the failure. It's simply a bit thicker when cold but at the same time offers more protection than 75W-90. If you said they put ATF in the differential rather than gear lube, then maybe. I realize everyone thinks these cars need to be treated like a fine swiss watch and they're as fragile as an egg, but both assumptions are 100% false. I used to run 75W-140 in my C6 on the track and while I haven't switched the C7 over....in fact I just filled with fresh 75W-90 since I was at 25 hours of use....I wouldn't think twice about it.
Fill Plug & Drain Plug
Obligatory track play-day photo
There's more to this story.
Last edited by 96GS#007; May 28, 2021 at 09:26 PM.
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So it starts out as a diff flush and now it is just a drain and refill? Good grief. OP, get off the computer and go down and discuss this with the manager...in person.
This place is turning into Bookface.
75W-140 didn't cause the failure. It's simply a bit thicker when cold but at the same time offers more protection than 75W-90. If you said they put ATF in the differential rather than gear lube, then maybe. I realize everyone thinks these cars need to be treated like a fine swiss watch and they're as fragile as an egg, but both assumptions are 100% false. I used to run 75W-140 in my C6 on the track and while I haven't switched the C7 over....in fact I just filled with fresh 75W-90 since I was at 25 hours of use....I wouldn't think twice about it.
Fill Plug & Drain Plug
Obligatory track play-day photo
There's more to this story.
Thanks for confirming as I also posted my 75 140 track experience with GM diffs. Of course GM/dealership will use any excuse, including “it’s not 75 90 fluid” not to cover this repair, but can you think of anything that’s special on the C7 diff specifically that would grenade the diff in 1k miles, due only to 75 140?
Thanks for confirming as I also posted my 75 140 track experience with GM diffs. Of course GM/dealership will use any excuse, including “it’s not 75 90 fluid” not to cover this repair, but can you think of anything that’s special on the C7 diff specifically that would grenade the diff in 1k miles, due only to 75 140?
I can't think of anything/reason. I'd also like to know how the dealer can look at the lube and determine its viscosity. Kind of doubt they had an onsite lab to test it.
I can't think of anything/reason. I'd also like to know how the dealer can look at the lube and determine its viscosity. Kind of doubt they had an onsite lab to test it.
Legally I do not think you can win. As strange has it may sound I believe even if you take your car in for an oil change and let say they do not tighten the drain plug and oil leaks on your way home and the engine is ruined...the company which changed the oil is NOT legally resp.
Best friend who was a Ford shop supervisor got a couple of quick lub screw ups a couple times a month. The quick lub's insurance always paid for the repairs. Sometimes with lawyers sometimes without.
The most important viscosity threshold #is the lower number.
75W was used so I think the gear oil is not the culprit.
75W-90 is the way go but I doubt the 140 jacked it up.
I’m hoping OP gets a resolution to this problem without having to pay a ridiculous sum of money, but if this does go to court, the 75 140 alone is weak. Again, if there’s something very specific about a base C7 diff that absolutely cannot handle this viscosity, that’s a different story, but that alone will be an uphill climb.
Keep us posted OP.
"So it starts out as a diff flush and now it is just a drain and refill? Good grief. OP, get off the computer and go down and discuss this with the manager...in person.
This place is turning into Bookface."
Brevity of retyping... It was drained, flushed, refilled. I watched the entire service of the diff both times. The second time I was down in the pit with them for the entire service. We looked at the fluids together, checked for material together, and so on.
"I'd also like to know how the dealer can look at the lube and determine its viscosity. Kind of doubt they had an onsite lab to test it."
They know because I explained to them what Grease Monkey put in.
When I took it in:
"there is a grinding noise coming from the car, the grinding only happens when turning. History of grinding was that it started after the diff service. Took it back to them to replace fluids/ warranty after the first service, which they completed. (so a total of 2 services). The first time they put in x fluid WITH limited slip additive. The second time they did NOT put in the limited slip additive." I also had the receipt/invoice from grease monkey listing the 75/140 and I showed them.
What happens if the oil used does not have the "limited slip differential additive"? Would this cause the grinding noise the OP referenced in the original post? The C7 differential has clutch packs that require the additive.
What happens if the oil used does not have the "limited slip differential additive"? Would this cause the grinding noise the OP referenced in the original post? The C7 differential has clutch packs that require the additive.
Grinding is from bearings that are bad. No limited slip additive will be popping or a shudder, particularly when making turns.
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Slideshow: A Jaguar designer's personal project imagines what a modern front-engined Corvette might look like if Chevrolet revisited the golden age of the Stingray.
uh....I think that they are
