Still a few Q's about changing diff oil.

[DZink24]

I have been searching the forums the last few days, gathering info on changing out my lube in the 2 differentials, and something has caught my eye. why must we use a synthetic oil in the diffs? why not a regular (dino) gear lubricant, for example that i see in tractor supply that is good in all heavy duty gearboxes and differentials? there was never any talk in any of the posts of anyone using a conventional dino gear lube oil in the diffs. i found that odd.



also, i have been seeing talk between the different weights, which would be better for an infrequent tower who would like to get the best mileage possible? 75 w 90 is what i am leaning to.



for those of you who have changed out the fluid yourselves, who has destroyed one of these "reuseable" gaskets? i'll believe "reuseable" when i see it. i will have replacements on hand... murphy's law will be in effect...



this is the first time i have changed the fluid on this truck (38,000 miles) i am guessing the consensus would be to completely remove the cover(s) and inspect the gears, as opposed to just loosening all of the bolts, letting the old stuff drain out, retighten, and refill?



2004 (9. 25/11. 5 axles).

thank you for your assistance

 

[jelag]

We only change the oil every 60-75K miles in the boxes... .

We've had no problems with several trucks and lots of miles on some of them... .

But we only use the factory oil... . or an approved full synthetic oil...

We build clutches and only use full synthetic grease in the clutch release bearings... . why, because our tests shows that the full synthetic product works better and lasts longer than the other products...

On the rear ends, we open them up, drain out the oil and use a suction gun to get the balance and than wipe out the bottom of the case with a rag and look for damage...

Hope this helps... .

 

[Ducman82]

id go for the 75w90, and i would also most deffenatly take the cover off. the gaskets arent bad, you can reuse if you do not destroy. it comes from the factroy with Syn. so i would stick with it.

 

[Spooled-up]

I agree with the above posters. I wouldn't use anything but synthetic since that is what the owners manual says to use. As far as the gasket, it feels like a metal ring encased in the flexible gasket. It's very tough and I can't imagine not being able to re-use it. it doesn't stick to the metal on the cover or the axle. It's a nice piece.

 

[mberry]

As stated before, it came with synthetic fluid from the factory. IMHO, Synthetic is way better than dino fluid on many levels and for many reasons. 75W-90 would be your best bet for mileage and protection since you stated you don't tow often.

I have changed the fluid in my diffs 3 times so far and all were before 65K miles. The gasket is tough. Keep your receipt since you'll be returning them unless you seriously damage them somehow.

Finally, removing the cover and inspecting the gears would be a really good idea at this point. According to your sig it's a 2004 w/38K miles. Good time to inspect the gears and assemblies while you still have a good amount of time and mileage left on your drivetrain warranty, if applicable.

Also, please make sure you change your transfer case fluid. If I don't do anything else I always make sure to change the transfer case fluid every 15K miles per the owners manual. Every time I have changed mine it looks like it has been used up pretty good and is rather nasty looking. I always use Amsoil ATF in the transfer case.

Also just so you know, there have been reports of some noise in the LS diffs when no limited slip additive was used. Even though they (AAM) say it doesn't need it, adding some LS additive seems to quiet them down if you run into that issue.

 

[rbattelle]

We only change the oil every 60-75K miles in the boxes... .
We've had no problems with several trucks and lots of miles on some of them... .

That's really good to know.

Every time I have changed mine it looks like it has been used up pretty good and is rather nasty looking. I always use Amsoil ATF in the transfer case.

The owners manual says to change the transfer case fluid? Is that something new? The service manual (up to 2003, anyway) makes no mention of a transfer case change interval. Guess I'll have to check my owners manual.

15k is awfully frequent for the transfer case... seems like 60k would be sufficient (unless you're running in deep water). I've been doing mine every 30-40k. Fluid looks brand new when it comes out.

Ryan

 

[Kry226]

The owners manual says to change the transfer case fluid? Is that something new? The service manual (up to 2003, anyway) makes no mention of a transfer case change interval. Guess I'll have to check my owners manual.



15k is awfully frequent for the transfer case... seems like 60k would be sufficient (unless you're running in deep water). I've been doing mine every 30-40k. Fluid looks brand new when it comes out.



Ryan

My 04 calls for a check interval of 30k with a drain interval of 60k. I change mine every 25k right along with the 48RE that I service at the same time.

 

[Joseph Donnelly]

You can use whatever premium grade lube you prefer. I run LE607 non-synthetic 90-weight. Synthetics may tend to increase the chance of seal leakage, particularly 75-90 weight lubes. I have used 75-140 synthetic also. I wuld remove the cover and look for debris in the bottom, wipe out the housing, etc. You can easily check backlash (with a magnetic base dial indicator) to see that it is reasonable, within factory specifications (0. 005-0. 007”). I like to change differential oil at about 35,000 to 50,000 miles, more often if the differential could have been submerged in water or exposed to a lot of dust.

 

[brods]

Lots of good info.



Imho, the first change should be sooner rather than later due to new parts wearing in. I changed the rear axle fluid at 17K and it had that sparkly metal flake look. In retrospect I should have done the first change at 2 or 3K to get rid of any break in debris. I changed it again at 56K and it looked like new. I have no concerns about going to 90K or more before changing it again.



Make your decisions based on how hard you work the truck and what you see when doing regular maintenance.



PS... before taking the cover off, don’t forget to clean between the cover and the housing, especially at the top. Any crud up there will fall inside the housing when you take the cover off.