I changed my front diff lube the other day. I used 75W90 Redline and filled until it began to lead out the fill hole.


I also replaced the fluid in my transfer case. I used Mobil 1 Synthetic ATF (Dexron III). I filled until it began to lead out of the fill hole.


Did I use the right stuff and the right amounts?


Thanks,


Terel

Spec call for 80W90 in the front axle and 75w90 in the rear axle. I am guess the reason for the 80w90 in the front axle is because GM "decouples" front axle thru spider gears that are constantly spinning in 2WD and they want a no less than a 80w in it for some reason because of this possible minimum film thickness. I am sure others use 75w90 but I do not nor would I recommand it in a GM IFS front axle without more data on the matter. The fill levels are okay though.

GM also recommends their 75W90 "Grape Juice" for the front Diff… See the following GM Tech link article for more info …

Synthetic Front Axel Lubricant (http://service.gm.com/gmtechlink/images/issues/feb03/TLFeb03e.html#story13)

http://www.dieselplace.com/forum/smileys/Geek.gif

For cold weather though you notice and it would not apply to CA. as they would never even see zero.

I don't think the difference between the two is worth being concerned about.

I used the same Redline 75W90 as terel. Fill till it runs out the whole. Never got around to doing the transfer case but I believe that works the same way... till it comes out the hole. I would have used Transynd probably since I have some around, but Mobil is decent tranny oil I suppose. I don't think you can go wrong with most of the big names.

I still use Dino oil, it is cheaper and I like to change it regularly too. Yes, they make 75w90 dino oil and have for many years. They even make a 75w80 and a straight 75 dino oil

Note this quote from the article linked by jpblock. Take note of the vent hose connector color. If it's black, you need to change it out as it's not compatible with synthetic lubricants.

"After changing the lubricant, inspect the front axle vent hose connector (fig. 17). The black type is not compatible with synthetic lubricants. If necessary, install vent connector 12479296, following the service manual procedure (document 843184).

TIP: If the vent hose connector assembly is white, it does not need to be changed."

Many here have changed the front diff to 75/90 and have many miles. Personally, I see no issues in doing it (and I did it too). Technically, GM recommends what it recommends, so you can take that as you will.


Most people in the "real" world have never checked, changed, or thought about the fluids in the first place, so you are better off than most.


Later.

Guys,


Thanks for the tips. Yeah, I read that I was supposed to use 80W90 in the front, 75W90 in the rear. Some time ago, I read from a well respected member here that it's okay to use 75W90 in both. I made the change, because it will be easier to keep one variety on hand and use it interchangeably in the diffs.


I had also read about the synthetic vs. non-synthetic compatible vent caps. Thanks for the reminder. Mine is white, so it's okay for me to use synthetic.


I was just not sure on the fill levels of the front diff and transfer case and wanted to confirm that Dex III ATF fluid was the right stuff for the transfer case.


All clear now. Thanks again!


Terel

That's pretty much what I did. I'm also running Mobil 1 in everything myself; engine, tranny, tcase and both diffs.

Although the Duramax supplement manual for 2004.5 lists non synthetic SAE 80W-90 axle lubricant for the front axle, I believe one of the techs posted a note a few months ago saying GM made a mid year change and is now using the 75W-90 synthetic grape juice for both the front and rear. This makes sense because it is consistent with the service bulletin.

http://dieselplace.com/forum/forum_posts.asp?TID=554&PN=1

I changed the original fuilds in my 2004.5 a couple of weeks ago, and the stuff in the front had the same grape juice smell as the stuff in the rear. I refilled both with the 75W-90 GM grape juice.

Does anyone have a 2005 manual? What is it showing for the front axle?