I got the news. It's actually the rear differential. It does the shudder like the transmission fluid thing. With mine it only did the shudder when I gunned it like a bat out of hell, and when shifting at top RPM to the next gear. At first Joel, the certified corvette mechanic, thought it was just the control module of the differential, which is a $100 part. But............he decided to have a look at the fluid.........Guess what? Chock full of metal pieces and shavings!
He said the service manager is going to call in and try to get it warrantied even though I'm a few hundred miles out of drive train warranty. He said they may cover it all or a portion.
Whatever it is I'm going to roll with it. For me this car has been the most fun and entertaining car I have ever owned.
I have previously had the torque tube replaced under warranty. I'll have to admit I drive the **** out of this car at the track once in a while and on the wide open highway. But the parts should have been able to handle it.
I can't wait to get it back. Weather in the 60s here and wanted to take a trip over to San Diego.
I guess my diagnosis of spark plugs was a little off. But can you blame me. I just had the car in to have them changed out.
Thanks for the suggestions.

 

Thanks for the follow-up. I have been watching this thread.

It is great to have a solid diagnosis. I hope you have success with GM.

 

The labor time for putting in the new rear differential is about 7 hours. Glad they found the problem. Now the waiting game for the part to come in begins.

 

Makes sense it was drivetrain related (I see it turned out to be the diff)... if it was plugs you should have had a misfire CEL.

 

Did you see the metal? How do you know they aren't saying whatever they want. It could be a bad plug install based on your description of the problem. The differential Is very far from the engine and would generally make some kind of noise if it was going bad while you drive, like a whine. Or it would have some play in the axles or something. Why would the diff be bad anyways? Did you use slicks? did you let it go dry? This whole things sounds too suspicious. Especially since most differential plugs when pulled will have metal shards/shavings all over it, especially the healthy differentials. This whole thing smacks of a scam.

 

Heres what I think happens everyday
1 you have an issue with plugs or plug wires (gap or wires not attached properly) which is identical to the symptom you describe.
2 you bring car to 'mechanic' who notices that you have no car technical ability, no idea what parts sound like or do
3 they notice the plug wire is loose or determine the problem is the plugs related $0 to fix
4 they decide to do 'extra inspection' and then tell you the truth that 'your diff is full of metal shards' which is true for healthy differentials
5 now they can charge you for a very expensive thousands of dollars that you don't need and don't realize has nothing to do with your issue
6 they might not even change the diff, just say they changed it and clean it and put new fluid in it (You might want to mark the old one) make sure you get the old parts back
7 even if they actually change the diff you still get charged a giant bill for what could be essentially a $0 to fix issue

A better way to deal with this issue is, to inspect and take pictures of any 'damage' yourself on the vehicle before letting them perform any work. If you post pictures here of the 'carnage' whatever they are telling you I bet its normal wear from the differential. If there was a serious problem it wouldn't match the symptoms you described. A failing differential will generally make alot of noise and not last very long. The way you describe the problem the car as if it will drive a thousand more miles and only has issues at WOT which sounds like plug related.

 

Good news! Even though the power train warranty has expired GM stepped up and is going to pay 90 percent of it. My portion will be $400 including labor for the new differential rear end, etc. If I had to pay it all it would have been $4,092. There is a module that fastens to the differential I will have to pay for. $600 for the part including labor. So my total bill will be a little over $1,000. They are overnight shipping the part and will start the process tomorrow to get me back on the road. I appreciate the dealer contacting GM and asking them to help on this. GM reviewed the maintenance records of my car and indicated to Bradley Chev that its close enough to the expiration that they'll take care of me. I'm a happy camper.

 

That’s great!!!!

 

Joe-
Is this your Stingray or the Z06?

 

z06

 

60k miles on a 2019- you're my hero.

 

Have the car back in my possession and it runs like a champ now!

 

Interested to see pics of new differential for the purpose of validating your purchase and making sure you didn't just spend $1000 for someone to just gap your plugs

This is a great advantage for you to have people with so much experience online able to help you identify fraud and criminal activity committed against you by taking advantage of your lack of knowledge about vehicles

 

 

It's a bit late now so hopefully the changed the diff which should be easy to spot. For future reference, I might suggest leaving a mark somewhere so you know if things were taken apart. Unless I trust the tech, I would probably feel better watching him do stuff even if it was with binoculars at a distance.

 

Yeah I told him to leave a mark already but no indication of whether they understood that it is standard practice for dealerships to charge people thousands of dollars for things they don't need, and then not even do them. That dude probably just paid 1k for them to snap a plug wire back onto a plug.

Ive heard it enough "Well hes convinced theres something wrong with the car and doesn't know how cars work, so lets just agree with him and find something that could stand to be replaced for 1k or 10k or whatever and then maybe do it or not idk"

 

^ Joe's a savvy guy and my money would be on him knowing when someone's trying to pull one over on him. If he's please with the outcome no reason for anyone else not to be.

 

Dude came to the forum for help with his car, I am giving him the best I can. Who am I? The best possible diagnostics master in the field of performance automotives, with the highest college education regarding the subject possible, close to if not the best engine tuner in the country. I've diagnosed, built, tuned, hundreds of cars, every kind of engine, I've seen everything there is to see, you can not surprise me or fool me.

The issue he described first, sounds like spark plug gap related and he recently had the spark plugs messed with so its 1:1 correlation there. Bad differentials don't cause engine misfires, they whine, clunk, stuff like that from the back of the car. They also coat drain plugs with metal, the healthy ones will do this, metal of a specific size range is normal.

I can clearly see the dealer is taking advantage of his lack of knowledge regarding the subject. His unwillingness to take picture of the differential plug coated with metal for us to see is working against him because perhaps in his mind he knows he is being taken advantage of and doesn't want to admit to that embarrassment online public forum.

We are not here to encourage his rash excess spending of money, or congratulate him for being a victim of a typical dealer bs. We are here to help. I can't just stand here and not point out the obvious problems with what has been laid out before us.

 

Not the dealerships or independent shops I go to where I have friends. Besides, GM is paying 90% so even if they are willing to screw you, GM might not be so willing to part with money. They will want the part back or at least on site for inspection. If they turn up and don't see the part, well, "I misplaced it somewhere" won't fly.

 

I Understand what you are saying, but there are many possibilities here, you must consider what bottom line is being fed,

1. $1k in the pocket: they created a fake invoice just between the 2 people working on the car (manager and a tech) that says something about a differential and GM knows nothing about this entire scam. This can be done easily with photoshop in 20 minutes to create fake bills, letter heads, insurance documents, etc... I hand you a paper and who do you pay? Did you pay with cash? How was the transaction occurring

2. they actually warranty and replaced the part legit, money went through the dealer, leaving the possibility that this was an unnecessary replacement of the differential. But why? Do they get paid some dividend based on service render? Is there a commission? I am looking for a motive why they would want to replace a part unnecessarily and I bet there is some connection between numbers and performing warranty work.

also
-A pic of the metal on the diff plug would have lended alot of feasibility and credibility to the claim that it was bad, why wasnt this done? They can't take a picture? Not advanced enough? No cameras? Sounds like BS

Just trying to make sure the fellow car enthusiast gets what he is paying for! I am a force for good and right