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Discussion Starter #1
Hello, Diesel Friends:


I'm changing my front and rear diff oil for the first time this weekend. I found the threads on types of oil to use very helpful. I'm choosing to use Redline's 75-90 synthetic. I crawled under my truck and found the drain and fill bolts just fine. Looks like it will be pretty straight forward.


I've never changed transfer case lube before. I'd like to do this while I'm under there. I'll get some Dex III equivalent (probably redline, too) for this. Can someone give me a step by step for doing this? It's probably pretty straight-forward, but again, I've never done it.


Thanks!


Terel


04 Sierra 2500HD Dura/Ali
 

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It is pretty much the same as the differential change. Has two plugs you will need an 18mm wrench just drain and refill.
 

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Discussion Starter #3
Great. Thanks.


I've read on these posts that when switching to synthetic gear oil, we need to make sure we have (or procure) the "white" cap, which is apparently more resistant to synthetics than the black one.


I found the cap on my front diff--it was white and about 3" in diameter. It was sort of facing the driver's side on the top of the front diff. This was it, right? (i.e.--no replacement necessary?).


I couldn't find a plastic cap on the rear diff. No change necessary here?


Lastly, I want to confirm that I bought the right kind of gear oil. Hoot mentioned I can use 75W90 in my front diff, even though it calls for 80W90. I just bought a bunch of 75W90 to use in both diffs. Redline had two varieties--75W90 and 75W90NS. My truck has a "locking rear differential". Should I have got the "NS" version, or did I order the right kind of lube?


Many thanks, guys.


~Terel
 

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Terel,

If you bought the 75W90 rear end grease you got the right stuff. The 75W90NS is for use in non-limited slip rear ends.

TC
 

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The G80 option is an Eaton locker differential and does not require a friction modifier like other varieties of "limited slip" differentials. The Duramax is factory specified for synthetic in the rear always. Synthetic is optional for the front and that's where the white/black vent cap issue occurs. Black for non-synthetic and white for synthetic.
 

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Discussion Starter #6
TC,


I feel REALLY stupid here, but for clarification, "locking differential" is the same as "limited slip", which is the same as "posi-traction"?


I'm obviously new to this arena. If anyone knows of a definitive website that explains drive-trains, including 4 wheel drive mechanics, differentials, etc., I would love a link. This is something I've always wanted to understand and have never known where to go. There needs to be a web-site called "Howdoesitwork.com".


Thanks,


Terel





Tsckey said:
Terel,

If you bought the 75W90 rear end grease you got the right stuff. The 75W90NS is for use in non-limited slip rear ends.

TC
 

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Terel, they are all "limited slip" which bascially means that there is a mechanism incorporated into the differential which will prevent one-wheel slip on slick surfaces, which a non-limited-slip or "open" differential will do. Posi-traction is a brand name. Eaton is a manufacturer and makes our (GM) G80 lockers. Here's a link to the G80:


http://www.automotive.eaton.com/product/traction_stability/lockingdiff.html


This one's even better:


http://www.torquecontrol.eaton.com/product.htm


Edited by: Idle_Chatter
 

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Discussion Starter #8
Thanks, Iddle_Chatter!


So Redline's 75W90NS is for non-locking (or Open Axle) vehicles?


~Terel
 

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terel said:
Thanks, Iddle_Chatter!


So Redline's 75W90NS is for non-locking (or Open Axle) vehicles?


~Terel

Nope, an "open diff" would use basic lube, just like our G80s. Can't be sure, but I think the NS stands for Non-slip and probably contains a friction modifier for the clutch and cone type of limited slip transmissions like Auburn which are mostly used in automobile limited slip applications. Try to imagine this - you use a synthetic lube for it's improved film and lubrication (or slip) characteristics - but because your limited-slip unit uses friction clutches to do it's thing, you have to add some *lubrication reduction* agent to your lube!



Anyhoo, we don't have to worry about all that with our G80 lockers!
 

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Discussion Starter #10
Got it. Thanks!


~Terel
 

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Terel,

Actually, yes, the Redline NS designation is for "non-limited slip" differenctials. It doesn't contain the friction modifiers that prevent chatter. Use the stuff you bought. If you are going to tow really heavy loads a lot of the time, use their 80W140. It contains the friction modifier and is intended for slower, heavy going.
 

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By the way there is a website called www.howstuffworks.com. I've not looked up the operation of differentials, but it might be there.

TC
 
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