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Discussion Starter #1
I changed the lube in my differentials on my 2003 yesterday. The rear was fine, just a couple of shavings on the magnet. The front magnet was coated with a very thick layer of something that looks like baby sh*t colored valve grinding compound. There was also a thick layer of nasty slime over that. Does anyone know what this is?



This GM gear lube sure doesn't smell like grapes, whose idea was that?



Good Luck,


DDog
 

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DuckDog said:
I changed the lube in my differentials on my 2003 yesterday. The rear was fine, just a couple of shavings on the magnet. The front magnet was coated with a very thick layer of something that looks like baby sh*t colored valve grinding compound. There was also a thick layer of nasty slime over that. Does anyone know what this is?



This GM gear lube sure doesn't smell like grapes, whose idea was that?



Good Luck,


DDog




That is a common thing with GM front diff's. Assembly Lube or Break-in Lube???


I changed and the front to regular Valvoline because it get's limited use and I did not want to change the breather out. The rear was changed out to Valvoline synthetic GL5





It is a good idea that you changed your fluid .





T
NYEdited by: GMC-2002-Dmax
 

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The magnet on my front diff had so much crude on it that it appeared to be wearing a sombrero!
And what I drained out sure didn't look like gear lube to me...
 

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Is the magnet you guys are refering to on the drain plug? When changing the rear differential fluid do you drain thru the plug or do you remove the rear cover to clean it out?
 

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JimWilson said:
The magnet on my front diff had so much crude on it that it appeared to be wearing a sombrero!
And what I drained out sure didn't look like gear lube to me...

Haven't changed mine out yet ~ haven't used the 4X yet. Did dip my finger in and the yeller stuff that everyone comments about looked to be like the cutting oil used in our HS machine shop class back in the 60's. I believe it contains some kind of additive to lubricate heavy contact loading of the surfaces. Accordingly, I don't see it as junque/problem. Plan to run it around in 4X a bit before drain & refill.
 

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Here are some pics of my front diff plugs at 5kmi..


Front Diff Plug - Before


Front Diff Plug - After








Edited by: jbplock
 

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RMAX said:
When changing the rear differential fluid do you drain thru the plug or do you remove the rear cover to clean it out?
I just drained it by the plug. It seems to be pretty far down on the bottom of the diff, so my guess is I got the vast majority of it out that way.
 

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jbplock said:
Here are some pics of my front diff plugs at 5kmi..
Yup, that's just about what mine looked like. Scary, huh?
 

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How many miles are on your trucks when you change out the front diff? Does the break in stuff that the factory puts in really do any thing? Mine has about 1500 miles on it with only about 5 miles of 4H and 1 mile of 4L. I have grape juice in my garage and was waiting for more miles on the front diff before changing. After hearing about these stories maybe I should change it sooner.


Any thoughts?
 

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I changed my front & rear diff, as well as my tcase, over to Mobil 1 at 3K. My tranny got flushed and refilled with Mobil 1 ATF at about 5K.
 

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Jim ~ about how many 4wd miles were on it then?
 

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duckdog, i am just reading this now however, my front end had precisely the same crap as you described. i didnt get it either!?"$%&*


anyhow, i fell more comfortable with mobil 1 syn in there..especially after hearing of pinion gear failures in the north when it got real cold...IBBY
 

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Discussion Starter #13
Mine looked even worse than Jim's pictures. I can not believe this stuff is really supposed to be in there. I might have about 4 hours of 4WD driving time on that front diff. This truck was new in August. I am sure glad I changed mine. I used the GM synthetic grape juice. I would still like to know what this is. One of my buddies did not change his, and he is having front axle problems. The GM dealer says the lube that was in there never needs to be changed, and the service bullitin about changing to synthetic does not apply, because Michigan is not a cold climate, can you belive that?


Good Luck,


DuckDog
 

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ShumDit said:
Jim ~ about how many 4wd miles were on it then?
The first time I did it there was only 5K on the odometer, of which maybe 50-60 were 4wd. The 2nd time was about 20K (when I switched from Amsoil to Mobil 1), but that time there must have been at least 300 miles of 4wd. The crap wasn't as bad the 2nd time around, but I was surprised at how much crud was still there.
 

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Jim,
Thanks for the heads up on the second change. I also did my first change at 5k with Mobil-1 75w-90 (per my pictures in the earlier post). I’m currently at 20k so I think I’ll do another change soon to see what I find. I also don’t use my 4WD too often but isn’t the front diff still turning and churning the oil?
 

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yes, from what i understand , the front gears are alway running..ibby
 

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I changed mine last weekend....at 30k miles. Oops. It did not look any worse than the above pic. I use 4wd quite often and no problems yet. I went witht the white vent cap and Mobil 1.
 

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jbplock said:
I also don’t use my 4WD too often but isn’t the front diff still turning and churning the oil?
No, it's not. When you're running in 2wd the front driveshaft is disengaged, so there's no interaction between gear sets.
 

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Can someone please explain the different vent caps do I need to change the caps if I go to a different type of gear oil, sorry if I'm missing something here... Please explain..
 

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The original breather vent cap on the front differentials of the 02's (and earlier) wasn't compatible with synthetic fluids. That cap was black. The new one doesn't have a problem with synthetics. That one is white.

If you're going to run synthetics in the front diff, and your truck isn't an 03 or newer, you should definitely consider changing the vent cap. It's easy to do, it's just a PITA to get at.
 
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