Milky Gearbox Fluid - What does it mean?

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Milky Gearbox Fluid - What does it mean?

Postby kmoushegian on Fri Jan 08, 2016 10:38 am

I recently purchased my '86 911 Coupe (my first 911). As part of the initial PM efforts, I replaced the gearbox oil and when I drained it noticed the color was a gray milky color. This seemed odd, since every manual transmission (Audi) I have replaced the fluid on, the draining fluid is dark brown. I thought perhaps the color may have been inherent in that of the previous fluid. As such I replenished the fluid and drove the car perhaps 1000 miles before, flushing and replacing with new. The photo attached shows the color of the draining fluid (same in both instances). In both instances I replaced the fluid with Castrol 80/90, per Bentley. Is this color a sign that detrimental wear (aka imminent gearbox rebuild) is occurring or is this coloring something that can be expected?

Note the drain plug magnet did have very fine metal deposits attached, no alarming amount, but no metal chunks.

Thanks in advance.
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Re: Milky Gearbox Fluid - What does it mean?

Postby ttweed on Fri Jan 08, 2016 12:44 pm

That sounds like moisture contamination--it turns grey and milky when water is mixed with the fluid.
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Re: Milky Gearbox Fluid - What does it mean?

Postby kmoushegian on Fri Jan 08, 2016 1:25 pm

Yes, others have said that too. If that is indeed the culprit am miffed on how it got there, especially after I replaced the fluid the first time; the car I know was not in any abnormal water situations.

Do you feel it is possible that the cool and moist SD evenings can bring such a level of moisture into the gearbox that would make the fluid that milky?
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Re: Milky Gearbox Fluid - What does it mean?

Postby Steve Grosekemper on Fri Jan 08, 2016 2:40 pm

That sounds like contamination unless the car has LSD.
A car left for years in a moist climate will do that.
I would drain it and send a sample in for analysis.
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Re: Milky Gearbox Fluid - What does it mean?

Postby kmoushegian on Fri Jan 08, 2016 3:13 pm

Steve Grosekemper wrote:That sounds like contamination unless the car has LSD.
A car left for years in a moist climate will do that.
I would drain it and send a sample in for analysis.


Moist climate makes sense. The original owner lived in Palo Alto, and there were signs while detailing the car that it experienced wet weather, this car was a daily driver.

With that said let's say it is a moisture in the fluid; other than tearing the gearbox apart what do you recommend for cleaning the moisture out. Perhaps performing a couple more "200 mile drive and flushes"?

If the gearbox has LSD how would that (or would it) contribute to the milky color and is it a problem issue? Also what is the best way to identify whether the gearbox is LSD?
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Re: Milky Gearbox Fluid - What does it mean?

Postby Steve Grosekemper on Fri Jan 08, 2016 3:30 pm

LSD check - lift the rear and spin one rear wheel. If the other spins the same direction it has a LSD.
If the clutches in the LSD are failing they will come apart and make a hazy color n the gear oil.
That is why I suggested an oil analysis which will tell you moisture level and identify contaminants.
Yes, just keep changing it.
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Re: Milky Gearbox Fluid - What does it mean?

Postby kmoushegian on Fri Jan 08, 2016 3:43 pm

Steve Grosekemper wrote:LSD check - lift the rear and spin one rear wheel. If the other spins the same direction it has a LSD.
If the clutches in the LSD are failing they will come apart and make a hazy color n the gear oil.
That is why I suggested an oil analysis which will tell you moisture level and identify contaminants.
Yes, just keep changing it.


Any recommendations on who offers such assessment services?

I assume that all gearboxes, regardless of wear, will exhibit contaminants as part of normal wear. Are the results of such tests easy to interpret to indicate a particular containment is evident AND at a level that warrants concerns about wear? Who would I consult to interpret such results?
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Re: Milky Gearbox Fluid - What does it mean?

Postby Steve Grosekemper on Fri Jan 08, 2016 7:02 pm

These are the guys...
http://www.blackstone-labs.com/
They will send you a test kit which you will mail away.
They will be able to tell you what is in there and what should be and shouldn't.
They are really good guys; I use them for most of the track cars under my care.
If they are unable to give the detail you are looking for try your local PCA technical advisor.
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