View Full Version : Eaton's Recommendations on Locking Rear Diff Service
"GM introduced the new body style in 1998. At the same time they upgraded
the differential and changed to a synthetic lube. The G80 is specifically
designed to give ultimate performance with this lube, and the lube contains
special additives that help reduce slip stick that occurs between the
clutches. the GM synthetic lube typically runs about 100+ degrees cooler
than mineral base lube, which is better if you do allot of towing or heavy
hauling. I would recommend that you stay with the GM synthetic, not Mobil 1.
If you don't tow or haul you could use the pre 1998 mineral lube without
degrading performance of the differential. this would be a cheaper option
but require more lube changes. "
"Axle tolerances of the 1/2 ton trucks are very tight. The recommended
procedure was to change lube after 500 miles of heavy towing, which would is
considered a break in period. This breaking period generates high heat
conditions in the axle which was found to degrade the synthetic beyond the
point of mineral lube. After the 500 mile lube change, the axle is broke
in and does not generate the high heat. If you use GM synthetic after the
break-in period, it can be considered "lube for life", although some say to
change it at 40,000 - 50,000 mile intervals."
"If you don't tow, don't worry about the oil change as it a waste of money."
"If your truck is pre 1998 or the old style, it comes with mineral lube. IN
that case you need to stay with mineral because the seals are designed to
work with it. If you changed from mineral to synthetic you'll cause your
seals to swell and eventually leak. It's ok to go from synthetic to
mineral because you won't cause swelling. many of your stop leak
chemicals effect seals in this manner, resulting in a short term fix but a
long term problem."
Allison Jettester
02-28-2002, 10:04
TxDoc,
I got this straight off the Eaton Webpage FAQ
http://www.torquecontrol.eaton.com/prod6.htm
"What type of lubricant and limited slip additive should I use with my newly purchased Eaton Limited Slip Differential?
Eaton strongly recommends utilizing an API-GL5 approved Mineral-Based 80W-90 Axle Lubricant and one 4-oz bottle of Limited Slip Additive (GM or Ford)."
I was getting ready to put Mobil 1 in, since it is API-GL5. Other than Eaton's above recommendation and since GM itself is going against this recommendation, why do you not recommend Mobil 1?
If you got your info about their using synthetics from Eaton, are they not also contradicting themselves?
Joe
mark45678
02-28-2002, 15:34
I have been using redline inthe rear end since 600 mile! except I am useing 90/140 weight. no chatter while cornering and locks up tight when it needs to !!! and its about 10 dollars a QT.....
DmaxMaverick
02-28-2002, 16:00
Allison Jettester
Both statements are correct. The Eaton limited slip rear end does require mineral based oil and additive. Synthetic is too slippery and the clutches don't get enough friction to engage and balance torque.
The [Eaton] G80 in the HD's and 3500's is not a limited slip rear end, by traditional terms. It is referred to as the "Gov-Loc" rear end. It does have carbon clutches, but they are engaged by a governor. Using mineral based oil and an additive in this rear end will very likely greatly reduce its useful life. The use of only mineral based oil, without an additive, wouldn't be nearly as bad. The design did not include the use of the additive, which, among other things, contains mostly acid. The acid prevents the oil in traditional limited slip rear ends from glazing to the clutch surfaces, which causes the chatter by preventing lubrication. Synthetic oil will not glaze to the clutches like mineral based oil, and over lubricates the clutches. The G80 in our HD and 3500 trucks do not maintain constant friction like the older limited slip models. It only engages the friction clutches when there is a given amount of differential wheel speed. This has many advantages. Namely the reduction of heat in the rear end, and greatly reduced wear of the friction clutches, as they are not under constant load. See for yourself. Jack up the rear end, both wheels. It will act like an open diff. when one wheel is spinned. Notice no felt friction (or there shouldn't be, anyway).
Why would anyone want to deny his rear end of the best lubricant currently available?
Hope this helps explain it.
Additionally, synthetic oil should be used in the front end of a 4 x 4. Although it is not under the same load, or used as often as the rear end, they are usually neglected by rare service. Mineral based oil will absorb water (from submersion or condensation) and decompose over time (Yes, mineral oils decompose, after all, it is organic. That is why old oil gets that rank smell). Synthetic oils have an indefinite static life. Cheers (Boy! This should stir the pot, not that it is intended to)
So...
In simpler terms, does our G80 rear diff require the limited slip additive or not? Changing my fluid this weekend with the $20 quart GM stuff. Thanks in advance
Kyle
No, our axles don't need anything but good synthetic GL-5 rated oil. No additives.
After long investigation the bottom line is that the only GM spec. is for GL-5 synthetic.
The post I made was a quote directly from Eaton's reply about what is okay and not okay for use in conjuction with the locking rear end option.
Back in November, I received the following:
"From Mr. Ralph Holmquist of Eaton, the maker of the locking differential:
"The maintenance schedule for the rear axle was developed by American Axle &
Manufacturing and GM truck based on multiple tests. The Eaton locker does
not require additional maintenance nor does it add heat to the lube. The
lube will darken due to the carbon wear on the clutch surfaces, much the
same as a disc brake pad & rotor. This does not damage axle components such
as seals or bearings. However, a new axle can produce excessive
temperatures (plus 350 degrees F) due to the ring & pinion breaking in that
will break the lube additives down. Avoid high loads, trailer towing and
high speed extended driving during the initial break in of the vehicle.
After the break in period axle temps will level at a much lower figure.
Lube changes are a good idea because the additives are replenished and
contaminates such as casting sand are eliminated. The axle is filled at the
factory with a synthetic 75w90 GL5 rating made by Texaco under part # 2276.
The GM service # is 12378261. This is the only lube we have done extensive
testing with to insure locker compatibility. The only negative to using one
of these other lubes is an increased potential for clutch chatter. This
really doesn't hurt anything and can be corrected by changing the lube. I
noticed in the latest GM owners manual the term "or equivalent" when
referring to the lube specification. Look for a GL5 rating on the bottle to
make sure the ring & pinion, seals & bearings are protected. Limited slip
additive is not needed."
The following information outlines the type of
rear axle lubrication utilized in GM Truck axles.
I. Fluid Type
II. The 1500, 2500 and 3500 GMT 800 Trucks utilize SAE 75W-90 Synthetic Axle Lubricant. The GM part number is 12378261 and the specification is 9986115.
More good information! Thanks TxDoc. First time I'd ever heard that about going from mineral to synthetic causing seal problems. Very interesting.
GM needs to pour some magic in their lube bottles if they're going to continue to ask crazy money for it. I'm betting my rear end (no pun intended) that Mobil 1 will work just fine :D
RealBigTruck
04-18-2002, 15:23
Anyone see a problem with running Redline 80W140 in the G80 rear diff? I've got a case of this stuff.
Gary
Maverick
04-18-2002, 15:34
Is the Amsoil synthetic gear lube GL5 rated?
Maverick:
Yes at least the 75W140 Amsoil Syn is rated API GL-5, that what I run in mine. I think Eaton recommends this weight for heavy towing.
Ed
See my previous post.
posted 04-12-2002 11:28 AM
--------------------------------------------------------------------------------
Just hit 1500 miles and have chosen to change engine oil and rear end lube. Get the junk out of it early. Purchased my own gm filter and Rotella dino oil (4gal @ $5.89). Had the local quick oil change location do the service for me. They charged me $39.99 for the rear end lube (Pennzoil 75-90w synthetic) and changed my oil and filter with no additional charge. They even primed the oil filter! Although I am new to diesels, I do not believe that any new noises have occurred.
Yes it is GL-5. Cut and past link below for more info.
www.pennzoil.com/TechData/pdsheet/DomesticMarketing/Gear&Transmission/pdf/GearplusSuperEW.pdf
[ 04-18-2002: Message edited by: konacat ]
[ 04-18-2002: Message edited by: konacat ]</p>
Tommy turbo
04-18-2002, 17:50
I changed my diff at 500 miles. filled with Castrol 75/90 gl-5 full synthetic. have 18000 miles now no problems.
DMAXMAVERICK (AND /OR OTHERS)--I just purchased Mobil-1 75W-90--it might have a modifier added. Will this be OK for the G80 locker or should I return it? The product sheet states it exceeds requirements for ALL car and truck rear axles, and reduces chatter in limited slips. It states it is suitable for all applications requiring API service GL-5. Please respond. Thank you.
[ 04-20-2002: Message edited by: gdblake ]</p>
DmaxMaverick
04-21-2002, 00:09
gdblake
Mobil 1 is a high quality lube and should work well with no worries. This, of course, is my opinion. I have not conducted any testing of Mobil 1 gear lube. The additives refered to with most synthetics is not the same as is needed to add to dino oil in a limited slip application.
Thanks so much, DmaxMaverick--I've really been hangin', hoping for an answer. Anxious to change the diff. Appreciate your response. Had a call into Mobil, but they were closed for the weekend. Best regards!
Allison Jettester
04-21-2002, 07:44
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
wangotango
01-07-2003, 23:07
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
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.
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
Ditto's to Don post. http://forum.thedieselpage.com/ubb/icons/icon14.gif
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.
smile.gif
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
04-03-2004, 09:47
Originally posted by wxmn6:
Do the front transfer case also use 75w-90 too? Hmmm, you should only have one...
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 (http://service.gm.com/gmtechlink/images/issues/feb03/TLFeb03e.html#story13) 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) (http://community.webshots.com/album/65684589edLUNA)
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… smile.gif
Thanks for very helpful information! :cool:
alaskanmax
09-19-2007, 22:41
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
09-20-2007, 03:37
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
09-20-2007, 10:24
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
09-28-2007, 21:36
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
SoTxPollock
10-04-2007, 10:29
Alaskamax, been looking at my pictures since I got back, sure like your state. I will be back, by the way I have been running Mobil 1 75-90 synthetic for over 100,000 miles now with a G-80 and no problems whatsoever. I run it front and rear.
jharden1
10-09-2007, 04:49
Saw a infomercial that claims it locks up at 25 rpm difference
DmaxMaverick
10-09-2007, 06:16
Never saw an infomercial about it, but Eaton states the Gov-Loc engages with a 100 RPM differential. It may sound like a lot, but it isn't. At 25 RPMs, you couldn't make a u-turn w/o it locking.
Turbo Al
05-24-2008, 16:17
I brought the rear end break in procedure back to the top of forums just to confuse everyone a little more LOL
Al
My manual seems to indicate that BOTH the front axle and rear axle have synthetic lubricants. No change is required. I'll go to Mobil 1 around 6,000 miles.
What rear and front axles do I have or how can I tell? My rear is locking and I have a 4X4. I intend to tow at least 11,000 lbs. I didn't read anything about changing my lubes after a break-in period. The truck hasn't towed anything yet. I intend this to be my last truck so it has to last at least 10-15 yrs and if I look after it and myself ;) maybe longer. I can do all my own fluid changes as I have access to a lift.
DmaxMaverick
02-03-2009, 20:39
What rear and front axles do I have or how can I tell? My rear is locking and I have a 4X4. I intend to tow at least 11,000 lbs. I didn't read anything about changing my lubes after a break-in period. The truck hasn't towed anything yet. I intend this to be my last truck so it has to last at least 10-15 yrs and if I look after it and myself ;) maybe longer. I can do all my own fluid changes as I have access to a lift.
All Duramax equipped trucks are the same. The rear is an AAM 11.5" axle. If it has a locker, it's the Eaton Gov-Loc. The front is a GM Corporate 9.25" IFS (I could be wrong on the size). The only gear ratio offered for these trucks is 3.73.
Changing the rear lube at the right time can be important. Once you've seen what comes out, you won't ask why (reminiscent to those with newborn children). And, soon after you begin towing a significant load (11K qualifies). Originally, we recommended a change at 5K with no significant towing. Or, after 500 miles of towing. If you are keeping your rig for all eternity (relatively), it could be different. Lube changes are cheap, and easy. Money very well spent early on. Work hardening and cleaning of the assembly junk is important for long life. In your case, I recommend an initial change (if over 5K), then another change after 500-1,000 miles after a significant towing experience. Also, be careful to not overheat the diff, which is easy when towing and new. Frequent stops (every hour or so) with a cooling period of 15 minutes is good. This ensures thorough work hardening of the gear set. You should have to do this for more than the first 500 miles or so, of towing. DO NOT use dino lube in the rear end, under any circumstance. As we've seen, the brand of synthetic lube hasn't shown any noticeable difference. As long as it's full synthetic (none of that "mix" stuff), it should be fine with any of the popular brands.
Thanks Dmax" I have only 1200 miles on the truck and no towing yet. I think I will change just before I start towing in the spring. I should be around 3000 miles by then. (The truck I mean. There are many-many more miles on driver and more than a few that were heavy tows.)
DmaxMaverick
02-04-2009, 13:17
Thanks Dmax" I have only 1200 miles on the truck and no towing yet. I think I will change just before I start towing in the spring. I should be around 3000 miles by then. (The truck I mean. There are many-many more miles on driver and more than a few that were heavy tows.)
That sounds OK. You could get away with holding off the first change until you have about 500 miles of heavy towing. It's easy to do, and can be done anywhere, and quickly. The diff has a drain plug, and the rear cover does not need to be removed. You may have to lower the spare to cleanly access the fill hole, though. The factory fill lube is good, it just gets full of junk. The heating/cooling cycles are key, though. Do it right and the diff will last your lifetime.
Okay I had my first 500 of heavy towing and went out to my local dealer and asked for the right amount of grape juice to do a rear end fluid change. He sold me three liters and said I needed only about 2.8. I drained the rear end and it looked gray and dirty and the drain plug had a small head of goo the consistency of plumbers putty. I then put in all three liters of the new stuff and I am about 1 inch below the filler hole. Am I OK or should I add more? BTW the owners manual says what kind but not how much. PITA for sure.
DmaxMaverick
07-15-2009, 18:39
Your level is OK. The later models had the service lube amount adjusted to reduce incidents of axle seal leakage. It was 3.8L, and is now about 3L, or about 3/4" below the fill hole. Anywhere between 1/2" and 1" is fine.
The goo you found (and hopefully cleaned) on the drain plug and the color is normal for a first/early service. It's all the fine wear-in metal particles.
Thanks DM. I will be looking at the front end, most likely before the winter.
DmaxMaverick
07-16-2009, 11:01
Good deal. The front end is often neglected (out of sight, out of mind). 2 qts. for that one. You can use the same lube as the rear, but any good synthetic GL-5 75-90 will do as well (for a LOT less $$).
SoTxPollock
12-01-2011, 17:18
How about an update, I now have 191,000 miles on the odometer, all on Mobil 1 differential oil full synthetic. The first 100,000 was 75-90, the last time I changed it I couldn't find enough of the 75-90 and had to mix in some 75-140 for the rear. I calculated the average based on the number of ounces of each and it averaged out to be 75-120. Just got back from towing very heavy, 15,500 5er, with truck weighting in at around 8,000lbs. Trip was 14,138 miles. Absolutely zero problems with the truck, except for the busted upper u-joint boots from those lousy Yukon washed out roads. I think I can safely say that Mobil 1 gear lube is a good as any, based on my driving. I'm still amazed that the rear gears could take the punishment of decending into Death Valley for so long a time geared down with all that weight pushing downhill. I wish I could have had a pyrometer on the rear differential to know just how hot it got. She's still rolling along as silent as ever. That being said, I just have to think that any full synthetic gear oil that meets GM specs would have done just as well. Yikes I just realized, I've run slightly over 100,000 miles already on the Mobil 1 Automatic Transmission fluid already. Time to go shopping for some fluids for Christmas and get some fresh fluids in the ole truck, we go a lot of miles to go yet and I'm looking forward to every one of them. Thank God for those evil Big Oil People who know how to make that stuff that good. Oh and by the way if you look around you no matter where you are, If its manufactured and you're looking at it. Thank Big Oil Corporations, that's where it all comes from, do the research, it will amaze you. I photographed a wall in a conference room at The Artic Caribou Inn in Prudhoe Bay and the list of items made from Oil and Natural Gas by those Evil Oil Corporations is so extensive it cover all 4 sides of the room which would seat about a hundred people, a fair size room the list runs from floor to celing all around the room and I could think of a lot more new items that wern't even around when they made that list. When I watch Our President attacking the Big Evil Oil Corporations like he has it just turns me off. How could so much ignorance rise to the top like that? It's difficult to understand. Everytime I fuel up I think about how we all just take it for granted that everything is just the way we want it to be for our trucks. How blessed we are that good people all over this planet have what it takes to explore, drill, accumulate, ship and produce everything we need, where ever we go. Sorry for the ..... No I'm not.......... it needed to be said and I said it. Travel on Diesel burners, we still have the most BTU's per gallon of affordable fuel available everywhere, and the outstanding lubricants that keep um rollin.
More Power
09-07-2022, 11:27
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.
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