I had little reply in tech forum so I am re-posting here... apologies about the cross post...

Symptom/Issue:

'05 6 speed that had it's diff fluid changed one year ago to AMSOIL fully synthetic. Diff is not overfilled and does not leak. Drove the car for 6 or 7 months with ZERO odor. Following my first track event in the summer there developed a very strong diff oil odor that would drift into the car every 5 minutes or so on drive. Replaced the diff breather and it's improved the issue about 60-70 percent, but diff fluid smell is still there every few minutes. Inspection of the diff breather revealed the old one's rubber or plastic washer was essentially gone/melted, etc... So the decrease in smell makes some sense. But I still get an unpleasant odor and would like to alleviate it.

Questions:

Is this just as simple as the brand of diff fluid I used?

Is the smell an indication it's burnt and needs replacing?

Would Mobil 1 or GM's fluid not smell? (or smell as bad)

TIA for any thoughts or solutions if anyone has had same issues.

-- BierGut

 

Questions:

Is this just as simple as the brand of diff fluid I used?
no they all smell the same it's the additive


Is the smell an indication it's burnt and needs replacing?
No new smells just as bad

Would Mobil 1 or GM's fluid not smell? (or smell as bad)
nope

TIA for any thoughts or solutions if anyone has had same issues.

now for where it is coming from.
it doesn't take much so the best indication is a dusty spot as the oil will attract dirt to it. There are many spots that a leak can happen
usually it is the oring on the side covers, next the axel seals. then fill and drain plugs, Vent & the input shaft seal between the trans and the Diff.. as I said clean it up with brake clean then watch to see where it gets dirty
the joints on the axel are black so it is really hard to see there wipe your finger over them and check it that way
good luck

 

It's been checked twice by technicians; private and dealer, but to what extent I am not 100% certain. I was told there are no leaks, but perhaps they just cleaned off the area above the breather. I would have to question them.

What I found interesting is the DECREASE in odor once breather was changed but not the elimination of odor. It correlated with the original breather lacking the rubber gasket the new one has.

 

it also might be thhat there is some oil they didn't clean up

as in if you want it done right...................

 

So true...

 

Everything Ernie said.

 

As mentioned above, the smell is the extreme pressure additives and they are in all diff fluids. My wife HATES that smell.

There are several leak paths out of the diff. Don't know if they are as common on the C6 as the C5, and assuming your 05 doesn't have a diff cooler, the diff gets very hot at the track - to the point of melting portions of the diff in very long sessions at hot track days.

Left axle seal - common failure point on the C5 diff and won't get better with time.
Vent - It will release some fluid mist as the diff heats up. It can melt if the diff gets very hot.
Speedometer sensor - on the top passenger side of the diff is the sensor for the speedometer. When I lost my left axle seal in a race back in 04 and lost about half my diff fluid, my diff got so hot this sensor melted. Speedometer went away with about 5 laps left in the race. I finished the race, then rebuilt the diff. If your vent melted, I suspect you've partially melted this sensor as well and this is likely your vent path. It is all but impossible to see unless you drop the diff.

If you can smell diff fluid, you are losing it. At a minimum, I'd top it off prior to each track day.

After about 10 years of racing, last year I finally added a DRM diff cooler to my C5. I think the diff runs much hotter than I had formally thought.

Good luck finding and correcting your leakage source.

 

Could it be that someone got diff fluid on themselves while servicing the car and now some interior part still has the fluid on it?

Nothing ever really gets that smell out of fabric...



good luck on the search!

 

Excellent post - Thanks. I know it misted all up under the car and as you mentioned, as the techs told me this is what they found. Examination of the original breather shows it melted inside so we know it got pretty warm. Thanks for the heads up about the speedo sensor -- but it doesn't sound like we'll be looking at it anytime soon. (Ha)

The level is currently fine. I wonder if the diff was originally over filled and this was, at least, responsible for some of the misting. I'll have it thoroughly cleaned up under there and we'll see if we continue to get odor.

The one comment that you made that is always in my head is "if you smell diff fluid, it's leaking somewhere." Somehow I just get the feeling it'll show itself after a couple of track events next season.

Thanks again.

 

I suspect your speedo sensor has partially melted (given you melted your vent) and then hardened when the diff cooled. It really isn't more than a plastic insert with an o-ring held into place with an external bolt on a tab. I believe it has a magnet in it that senses the gear teeth as they rotate by it. The magnet is probably still in place since your speedo works, but my guess is that either the o-ring or plastic insert has melted and there is an air gap. I don't remember the size of the bolt, maybe 10mm. You might be able to get your hand up on top of the diff and get it off to inspect it.

I do not believe left over diff fluid is your problem as that will dissipate rather quickly when you get everything hot. If you notice the smell more on long sessions than short, almost certainly you have a leak that gets worse as the diff heats up.

 

Car is in the shop now so I am waiting on news...

If it's the speedo sensor that has melted, what remedy does one have for an upgrade to this doesn't just continue to happen?

 

wrap the sensor in some heat tape summit racing has it

 

Thanks, Ernie.