Opinions on possible metal in diff fluid

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19
Location
South Carolina
I recently installed a new manual transaxle in my fwd car. I used Redline 75-90ns. After 2000 miles I dropped the fluid out and installed fresh just bc I've heard this is a recommended process after installing a new unit. I've had some loud whining noise from the transmission, could be normal, might not. Its got shorter gearing and the preload might be tighter on the output shaft, or it could be too loose which is my concern. But sound aside I took pics of the fluid I took out, just looking for opinions on if it looks normal, almost looks like it has metal particles but I'm not sure. The magnetic drain plug had no fragments on it, just a very tiny amount of metallic dust.

First Pic is it just poured out after parking it from driving, second is after I stirred it. Does it look normal or not...? Thanks all.
IMG_20200827_180306449.jpg
IMG_20200827_180235884.jpg
 
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Messages
1,965
Location
USA
Hard to tell from those pictures

For the purpose of analysis, you would be better to use a mason jar. (let it separate)

Then you can do field tests with flashlights, laser pointers to get a rough idea of what all is happening with the fluid.

People are often surprised at what a good field test can reveal.
 

Papageorgio

Thread starter
Messages
19
Location
South Carolina
Hard to tell from those pictures

For the purpose of analysis, you would be better to use a mason jar. (let it separate)

Then you can do field tests with flashlights, laser pointers to get a rough idea of what all is happening with the fluid.

People are often surprised at what a good field test can reveal.
Thanks for the advice, I'll do that in the future.
 

JHZR2

Staff member
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46,023
Location
New Jersey
I’d say something isn’t right.

Reminds me of the diff fluid from my 82 Mercedes. Which does have a whine at 40-60, and a clunk on and off throttle.


My drain pan was filthy before the job so don’t mind all the chunks you see there, but I had A lot of metal flake.

How sure are you that your system was clean before you installed it?

For me, the fluid that came out in the above might have been the only change in that differential, and I did it maybe 8 years ago...
 

Papageorgio

Thread starter
Messages
19
Location
South Carolina
Not sure on how clean it was when I got it, it was a new transaxle that was opened and had a limited slip unit and gears installed.

Glad you mentioned the noise, yes mine is the same as you described 40-50 it's the loudest, gear doesn't affect it. Does it most when I'm cruising down the road light throttle, goes away quite a bit when I get on or off throttle. But I always hear it when coasting down in or out of gear through the 40-50mph range. Lots of whine in it.
 
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1,965
Location
USA
When you said new, new as in brand new? reman? You install?

If no mechanical clunks or shudders etc, this sounds like finish/lapping as described as high pitch and could be normal ( just taking longer)
 
Messages
3,020
Hard to tell from those pictures

For the purpose of analysis, you would be better to use a mason jar. (let it separate)

Then you can do field tests with flashlights, laser pointers to get a rough idea of what all is happening with the fluid.

People are often surprised at what a good field test can reveal.

Good advice here. Amazing how it separates. Reveals a lot for no cost.
 

Papageorgio

Thread starter
Messages
19
Location
South Carolina
When you said new, new as in brand new? reman? You install?

If no mechanical clunks or shudders etc, this sounds like finish/lapping as described as high pitch and could be normal ( just taking longer)

Brand new from Gm and a known shop installed the gears and lsd unit. No clunk or shudders, works perfectly fine without issue. The noise alerted me, the fluid had me wondering. And like I stated earlier no metal shavings or chunks. I took out the speed sensor so I could see the ring gear teeth and they look great.
 
Messages
1,965
Location
USA
Can you elaborate on the finish/lapping,, and just taking longer statement, thanks much

Sure, in spite of best machining processes, no gear set is perfectly mated.

Even those that are close are then subject to installation tolerances, various housing flex, lubricant's selection and actual usage.

So there is a period where they must wear to each other. More gears- more time.

Higher pitch noise "generally" indicate ( there can be other things too but you don't mention excessive heat or other symptoms) 2 finishes mating.

Lower pitched noises generally indicate asperities mating.

Based on your account ( you say no other issues noticed) I think you most likely have an extended gear mating ritual so rent them a room and let it work itself out. ( but keep an eye on it)
 

Papageorgio

Thread starter
Messages
19
Location
South Carolina
Sure, in spite of best machining processes, no gear set is perfectly mated.

Even those that are close are then subject to installation tolerances, various housing flex, lubricant's selection and actual usage.

So there is a period where they must wear to each other. More gears- more time.

Higher pitch noise "generally" indicate ( there can be other things too but you don't mention excessive heat or other symptoms) 2 finishes mating.

Lower pitched noises generally indicate asperities mating.

Based on your account ( you say no other issues noticed) I think you most likely have an extended gear mating ritual so rent them a room and let it work itself out. ( but keep an eye on it)
OK, excellent info, I'll put new fluid in, drive it and keep an eye one it.
 

Papageorgio

Thread starter
Messages
19
Location
South Carolina
OK, excellent info, I'll put new fluid in, drive it and keep an eye one it.
Just out of curiosity and for future reference, what would a bad output shaft bearing sound like, a grinding noise or a whine type noise? I found some info on a bad input shaft bearing which seems more common but couldn't find any specifics.
 
Messages
1,965
Location
USA
Just out of curiosity and for future reference, what would a bad output shaft bearing sound like, a grinding noise or a whine type noise? I found some info on a bad input shaft bearing which seems more common but couldn't find any specifics.

First, there is no standard or measurement of "bad" in terms of a bearing (no OEM or ABMA or vibration standard will publish or admit to any criteria- the best you can get is a "defect" rating) and there's a good reason for that but beyond the question in your post but I need to establish a baseline.

In reality, at least half of all bearings diagnosed as "bad" are well within service life so technically they are "mis" diagnosed leading to false standards to evaluate by which unfortunately the internet ( and many actual training books on the subject) are full of.

Assuming a properly selected, installed and maintained bearing......

"whining" ( high or low pitched) is generally indicative of a lubrication issue or in advanced cases the finish of the bearing has polished ( bearing is now in a failure state)

"grinding" is almost universally either severe overloading causing rolling media to hit or skid or a geometry issue where the bearing is not running true to its axial or radial degree of freedom.

In either case, more times than not, the "bearing" will be the resultant failure of another failure mechanism- not the initial one.
 
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