Eaton's Recommendations on Locking Rear Diff Service

[Allison Jettester]

DmaxMaverick,

I've been in Rota, Spain for the past few weeks and didn't see your post answering my post above. I had the mind set that the whole question and answer page on the Eaton website I quoted referred to the G80 Locker. They changed the subject to limited-slip and I didn't catch it (I should have since that is the kind of thing I always look for when reviewing government specs!).
Thanks for straightening me out. That's one thing good about this forum--if you are in error, someone with sharp eyes will catch it.

Anyway, you are correct (as far as I know) that any GL-5 rated synthetic gear oil should be ok in the G80 Eaton's "Gov-Loc" LOCKER. Now that I have bought both Redline (with additive) and Mobil 1 I am going to have to make a decision on which to use.

Also, I did jack up the rear and there was a LOT of friction in the rear when I turned one wheel. I could hear a lot of noise coming from it. I do believe the opposing wheel did turn in the opposite direction like an open diff, but am going to do this again to be sure.

Thanks again,
Joe

[DonG]

TTT

[wangotango]

Am using Almasol 607 from Lube Engineers Inc in a Mag-Hytec rear-end cover.

Towin' like a mutha. No heat/wheel drive issues.

w/t

[wxmn6]

Two different fluid to choose from: 75w-90 & 75w-140. Can someone please explain the difference, what each number represent? I'm not too familar with how the fluids are rated. Thanks.

[DonG]

wxmn6,

The two sets of numbers refer to the thickness or viscosity of the oils. Very similar to motor oil like 15W-40.

The 75W-90 weight gear oil is what comes in your truck differential and is recommended most of the time.

The 75W-140 is listed in your operators manual as an alternative gear oil if your tow heavy loads in hot weather. Heavy loads would be 12,000 lbs. or above. Several people on this site feel that even when towing heavy, the 75W-90 will still be fine.

When towing 14,000 lbs. I use the 75W-140.

I hope this helps.
Don

[jbplock]

Ditto's to Don post.

Also another point regarding the numbers in an oil viscosity spec…

The high number (90 in 75W-90) is measure of the oil’s viscosity when it reaches operating temperature and the low number is a measure of the oil’s cold temperature viscosity.

So, 5W-40 and 15W-40 oil have the same viscosity at operating temp but the 5W=40 will flow better when cold.

Conversely 75W-140 oil will be “thicker” when hot than 75W-90 oil but have similar cold temp performance.

[img]smile.gif[/img]

[wxmn6]

Thanks for excellent information. It's nice to learn about something like that.

I am just curious that if both 75w-90 and 75w-140 have same cold weather performance (which I was concerned because I live in NY where we can see sub zero temperature during the winter), then would it hurt to go with higher viscosity if you don't do alot of heavy towing? I would assume that thicker oil would give more protection? Would it (140) actually do more harm than good (than using 90), or is it just that 140 cost more than 90?

With the information given earlier, I will be going with 75w-90, but just want to learn a bit more about it.

Do the front transfer case also use 75w-90 too? If I am not mistaken, the front transfer case does not have factory sythetic, correct? If I want to go sythetic, is there something else that I need to do (other than draining) to properly clean the case so it would not get contaimated with mixed fluid? Thanks.

[G. Gearloose]

Originally posted by wxmn6:
Do the front transfer case also use 75w-90 too?

Hmmm, you should only have one...

[jbplock]

Originally posted by wxmn6:
... I live in NY where we can see sub zero temperature during the winter), then would it hurt to go with higher viscosity if you don't do alot of heavy towing? ....

Does the front transfer case also use 75w-90 too? If I am not mistaken, the front transfer case does not have factory synthetic, correct? If I want to go synthetic, is there something else that I need to do (other than draining) to properly clean the case so it would not get contaimated with mixed fluid? Thanks. [/QB]

wxmn6,

I’m not an expert on this subject but from what I’ve learned unless you are towing big loads regularly it’s best to stay with the GL-5 synthetic 75W-90. Using the heavier 75W-140 when not needed can lower your fuel efficiency.

And yes last I knew the front diff comes with 80W- 90 mineral oil but you can switch to a GL-5 synthetic 75W-90 (the 4WD transfer case uses DEXRON III). However, GM recommends you have the “white” vent cover on your front Diff for compatibility with the synthetic oil. See Feb03 GM Techlink article for more info.

It’s also not necessary to flush or clean the diffs (front or rear) when doing a routine fluid change to synthetic – the fluids are compatible. Just remove the magnetic plug, drain and refill. Also clean the plug ... the front diff plug on mine had quite a bit of “goo” on it. A small amount of metal filings is normal. (see pics)

Personally I changed both front and rear diffs to Mobil-1 75W-90 at 5kmiles. I also changed the transfer case and Allison to Mobil-1 ATF.

A search of the forum will also turn up a quite a bit of info on this subject.

Hope this helps… [img]smile.gif[/img]

[wxmn6]

Thanks for very helpful information!

[alaskanmax]

According to some folks on the forums it is said that if you lift both rear wheels on the d-max, and rotate one wheel the g-80 limited slip will act just like an open diff and the other wheel will counter rotate. With out opening up my cover on my rear diff or getting stuck how will I know for sure what my used truck has??? I can find no stickers on dash or door areas to say it has a g-80

[DmaxMaverick]

According to some folks on the forums it is said that if you lift both rear wheels on the d-max, and rotate one wheel the g-80 limited slip will act just like an open diff and the other wheel will counter rotate. With out opening up my cover on my rear diff or getting stuck how will I know for sure what my used truck has??? I can find no stickers on dash or door areas to say it has a g-80

Look in the glove box. Your RPO sticker is there, and G80 will be on that list, if you have one.

If you raise both wheels and spin one slowly (tranny in P), the other wheel should turn the opposite direction. If you spin one very quickly, like a good kick, it will lock. You can also test it on a roadside shoulder, one wheel on the pavement, and the other on loose ground (less traction). You should feel it lock when you goose it and one wheel breaks traction.

[SoTxPollock]

ALASKAMAX, where are you located? I may have seen your truck, seems to be the truck of choice where I was last week, sure miss those 50 degree days, came back to 90 degree Texas days.
One word of caution when the locker locks, if you are on slick hard surface be prepared to back off the accelerator or you could find yourself going around in circles. On an open rear end at least one of the wheels will tend to help you keep it straight, but if both start to spin the engine torque and rear differential torque will tend to make the truck back end slide to the right. Enjoy the truck.

[alaskanmax]

I, and truck are both in Anchorage. Today, I recieved my copy of Differentials Identification, Restoration & Repair by Jim Allen and Randy Lyman. I have read most all in the past couple hours, so listen up everyone....buy a copy as this book is really good and will answer any questions on the AAM 11.5/Eaton G-80. ......Thank You to Jim and Randy

[More Power]

The early trucks were equipped with convention petroleum lube in the front axle. But, apparently some 4x4 trucks had problems with their front axle when driven in cold environments. This caused a change in lube recommendations for later trucks. And, GM produced a service bulletin for the older trucks, which allows them to use synthetic lube (once a specific part is swapped for one that is compatible with synthetic).

Bulletin No.: 03-04-19-001B, Date: September, 2004

Use Synthetic Axle Lubricant, P/N 12378261 or P/N 89021677 (Canadian P/N 10953455 or P/N 89021678). Each of these part numbers is the same axle lubricant, with differences in packaging only. Fill to a level between 6 and 9 mm (0.25 in to 0.375 in) below the bottom of the fill plug.

If the vent hose connector is black in color, it will need to be changed so that the 0-ring seal is compatible with the synthetic lubricant. Install vent connector, P/N 12479390. Follow the Front Drive Axle Vent Hose Connector Replacement procedure in the Service Manual.