Some advice for Corvette owners re diff oil

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Right after I got my (new to me) 2005 Corvette, I had the dealer change the transmission fluid and the rear differential fluid. Within a day of having this service done, I started getting weird scrubbing and crunching noises in low speed, tight turns (like in the cul de sac at the end of my street). I checked the dealer invoice to see what diff oil they had used and it was GM part #88900401 full synthetic 75w90. I looked this up online and it is not a limited slip diff oil and there was nothing on the invoice to indicate that they had added any limited slip additive. I called the dealer about this and was told that 88900401 is the diff oil listed in their computer as the correct oil for a 2005 Corvette and no limited slip additive is needed. Okay, but what about this noise? They wanted me to bring the car in and leave it with them for a full day so they could diagnose the noise. I had an appointment for them to do that this past Friday and they were going to give me a loaner car gratis for the whole day.

However, earlier last week I did a lot of research about this online and I discovered 88900401 is NOT the correct fluid for C6 differentials. GM issued a TSB (#07-04-20-002A) in 2008 detailing this noise from the differential and specifying a new gear oil that was specifically developed to eliminate chatter from the clutch pack of the limited slip diff on the C6. The new oil is Dexron LS 75w90, GM part #88862624 and it's been the factory fill in all Vettes (C6 and C7) since the 2008 model year. So, long story short, I decided to forgo the appointment on Friday. I went to the dealer and bought three quarts of the Dexron LS ($26 a quart!) and had my local shop change it out. Noise gone. Problem solved.

So, if you have a C6 Vette and ever have any strange noises from your rear end, or just decide to change the diff oil as a preventative measure, be sure to use the Dexron LS, part #88862624.

full-559-1928-dexron_ls.jpg
 
I was just about to bring up the Dexron LS fluid but I finished reading your post and you got it. Good job doing your due diligence. I've heard so many horror stories from Corvette owners going to the dealer. They just follow that computer without question. My cousin had a dry sump Z06 that needed 11 qts for an oil change and they thought it was the 8 qt wet sump. Good thing he read the invoice before he left or he would have probably seized up his engine.
 
Originally Posted By: userfriendly
https://www.youtube.com/watch?v=tTGZOJQQBeE

Even the locker type has a clutch pack, so it would be better to have a LS lube and not need it,
then need a LS lube and not have it.

GM did not invent a gear oil specification. Popular opinion is any name brand GL-5 75w90.

www.eaton.com >> products & solutions>>


Not sure what you're getting at, but there is plenty of anecdotal evidence on the various Corvette forums that a standard limited slip gear oil used in the C6 differential will ultimately result in chatter from the clutch plates binding (even Mobil 1 LS). There is simply not enough LS additive in "normal" limited slip diff oil to do the trick in these Getrag rear ends. If you notice the TSB # I listed above, it's Revision A, issued in 2008. The original TSB, issued in 2007, called for the regular gear oil to be used (the factory fill at the time) with a DOUBLE treat rate of LS additive (8 oz instead of 4 oz). This still didn't cure the problem, so GM had the Dexron LS fluid developed which has a boat load of LS additive in it. And like I said, this has been the factory fill in the Corvette diffs since the 2008 model year and has completely eliminated the problem.

Here is what's in the 2016 Corvette owner's manual:

 
Originally Posted By: AIRJAC3
....Good job doing your due diligence....

+1 Was thinking the exact same.

If a GM dealer, rather disappointing to put it kindly that a/the dealer wouldn't have the updated spec in their computer. Good I suppose they were willing to give you a loaner free.

Glad your issue resolved.
 
Clutch plates in LS diffs have been chatterin' since I was a kid. Gotta catch ye a sperm whale and add just a touch to stop their noises.

I had a 78 Firechicken with factory limited slip and it would kerchunk to a stop and really scare you. But a dab of whale oil additive made it all go away...
 
Originally Posted By: SteveSRT8
Clutch plates in LS diffs have been chatterin' since I was a kid. Gotta catch ye a sperm whale and add just a touch to stop their noises.

I had a 78 Firechicken with factory limited slip and it would kerchunk to a stop and really scare you. But a dab of whale oil additive made it all go away...


Well, mine ain't chatterin' no more.
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You betcha!

BTW, I spent a lot of time in two different C5's. Great runners with just minor mods, headers and a tune and they would really get it!
 
There's NO WAY I'd leave a Vette with a Chevy dealer all day. It is highly likely they would beat the living heck out of it. I would wait for it and keep a close eye on it, standing in the bay watching them.

Good thing you skipped that apt!!!
 
Originally Posted By: SteveSRT8
You betcha!

BTW, I spent a lot of time in two different C5's. Great runners with just minor mods, headers and a tune and they would really get it!


Bone stock, a 2005 C6 with the 4-speed auto, will do the the quarter in the 12 to 13 second range at 110 to 113 mph. This is the first car I've ever had with enough horsepower to scare me. The 4L65E transmission is geared extremely low in first gear, and when you stomp this thing at low speeds, the neck-snapping acceleration is almost overwhelming. You're doing triple digits in the same amount of time it takes most cars to get to sixty.
 
For any performance car, you have to know what fluids are needed/recommended for the vehicle before ever taking it to a dealer. This is even more important for manual transmissions and rear differentials.
 
FWIW I keep folders on my computer for Ford and Mazda, the 2 lines we carry, with every fluid note I can find. I add the new charts every year but keep the old charts as well just as a reference.
 
The LSDs in the E24 M6 and E28 M5 were notorious for making grinding noises during tight low speed turns. A little extra LS additive quieted them right down.
 
Originally Posted By: MCompact
The LSDs in the E24 M6 and E28 M5 were notorious for making grinding noises during tight low speed turns. A little extra LS additive quieted them right down.


Do those have a clutch type or a Torsen diff?
 
Originally Posted By: bdcardinal


Do those have a clutch type or a Torsen diff?


Clutch.
 
Originally Posted By: MCompact
Originally Posted By: bdcardinal


Do those have a clutch type or a Torsen diff?


Clutch.


Interesting. I thought BMW would use a Torsen type diff considering they are geared more towards performance driving on twisty bits. Same with Corvette for that matter.
 
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