Lots of great help on this site, and since there's so many newBs (like me), thot I'd summarize what I've found:

Most tell you to change engine/diff fluids in the 1st 500 - 1K, plus do the Ally filter (if you went slush box). It's good to get a few tow or HD miles on the rear b4 doing a fluid change, just because the ring and pinion seat (wear) differently under load vs. no-load. I opted for a couple of hundred miles of towing.

It takes almost a full 4 (four) quarts to fill your rear diff. Don't bother to look in your manual for the quantity of oil, GM doesn't think we'll ever need to change it, or need to know how much it holds (or somesuch), It calls for synthetic 75w 90, I went with the Mobil 1. The Mobil 1 comes in handy 1qt bottles with a fill tip, and between having a drain plug and using these bottles, changing the rear diff was a breeze.

Mobil 1 M1-301 filter seems the best engine oil filter, found it at Autozone (thanks to help from this site). My factory filter was on Gawd Damn Tight, so be prepared for that (I literally crushed the old filter getting it off). I went with the Chevron Delo 400 15w 40, found at our local Costco, but then again, I'm a Chevron retiree, and know this stuff rocks :ro) . If you have the skid plate package, beware that as a cruel joke, GM engineers decided the plate should be so protective (read big) as to catch the draining oil when it is anything but the initial full pour-out force of a full oil pan, so next time, I'll slightly jack the truck up from the front and passenger side (that corner needs to be the highest after jacking), because it took me a half hour to clean up the mess :( . Also, your oil add cap will be tight (mine was) but it's not a screw off, it takes like a 180 deg. turn and pull up on it, then lube the O ring before you put it back on.

DON'T try to change your Ally filter when the tranny is warm!!! :eek: Let's just say that you should be prepared for a trans fluid shower if you do (don't ask me how I know :o: ). Fill the new filter with some good Dextron III and if you spill a significant amount in the change, add accordingly. This is so easy to do, that you'll forever love Allison trannys for it (other than this one I have runs warm, but that'll be fixed).

Oh yeah, and if you plan on keeping the tires that came on it, it's time to do the 1st rotate at 1K mi. before any wear patterns set in, then every 5k after...

It's the little things sometimes... That's all from me :cool: (for now!)

:grd:

Related to the allison spin-on filter, a couple of things I learned...

1. Don't forget the magnet - it is a donut and sticks to the old filter when you take it off...

2. Only use the factory allison filter. Napa (made by wix or baldwin) has the holes in the wrong location - the filter magnet partially obstructs the fluid flow and can lead to harsh transmission action.

- jeff

to add to the filter thing, gmdieceltech sells all the filters, i just pick up a full set plus the WIf senser wrench, which is really nice.

The hole locations on the NAPA filter has been discussed several times. The general opinion is that because of the slight slope to the face where the holes are physically located that there is more than enough room for the fluid to flow past the magnet.

Related to the allison spin-on filter, a couple of things I learned...

1. Don't forget the magnet - it is a donut and sticks to the old filter when you take it off...

2. Only use the factory allison filter. Napa (made by wix or baldwin) has the holes in the wrong location - the filter magnet partially obstructs the fluid flow and can lead to harsh transmission action.

- jeff

Dang it! I should've written notes! I caught that (the magnet), but especially wanted to mention it in my note (which I promptly forgot :o: ). Thanks for the reminder, Jeff!

The hole locations on the NAPA filter has been discussed several times. The general opinion is that because of the slight slope to the face where the holes are physically located that there is more than enough room for the fluid to flow past the magnet.

I wouldn't use it. I put my napa on without the magnet and went and bought a new allison filter for my next change. Why risk it. Sorry - how many folks on this site are qualified to do an analysis of the flow - zero...

- jeff

so how often and when to change the filter on the tranny? you can just unscrew the filter and all the fluid won't pour out? How often, when, and what kind of fluid do you put in the tranny?

Question #1 : How often do you change the tranny filter?

Answer : There is a tsb to change it at first oil change and at every fluid change after that. I will change mine out at 1000 miles.

Question #2 : Can you just unscrew the filter to change it without too much fluid?

Answer : Yes. You can just unscrew the filter with less than a quart of fluid loss. Fill the new filter prior to installation and you won't even have to top it off when you are done. Don't forget the filter magnet when you install the new filter.

Question : What is service interval for transmission and what kind of fluid can be used?

Answer : The service interval is 25k miles severe and 50k miles for normal service. Any good quality dexron-III rated tranny fluid is fine. I buy cases chevron atf from costco and drop the fluid in the spring and replace the tranny fluid as well. It's so inexpensive that it's cheap insurance to change it out every year. The chevron atf is very highly rated by the oil experts over on bobistheoilguy.com.

For synthetics - some use mobil-1 atf, others use castrol transynd. I used to always use synthetics - but the dino oils and fluids are so good these days, along with their additive packages, that I don't see the need any longer... If I lived in an extremely cold climate, I would still use them....

- jeff

Quick question.

I contacted my dealer today and got a quote of $129 to change the rear differential fluid. This seems a bit HIGH to me! What all is involved in this process (never done it before). And could I/should I just do it myself?

Also, I assume that the drain plug is that little do-hickey at the very bottom (underneath) of the pumpkin, but how do I remove it?

Thanks in advance!!!!!!!!

The oem synthetic fluid is the only thing that is approved to go in the rear differential. It costs $22 per quart mail order through gmdieseltech.com; I think it takes 4-5 quarts. It is dyed purple so that GM can tell if you are using their super special stuff. And, no you cannot officially use mobil-1 synthetic because it does't meet GMs specs - but everyone does anyway! :)

So, to answer your question - given the high cost of GM's synthetic gear oil - the dealer price isn't as bad as it might initially sound. Should be the cost of fluid + .5 hours of the tech's time.

- jeff

Thanks dmax lover... I appreciate the heads up! And you're right, given the price of the fluid their price isn't out of line after all. I'll just have them do it when I'm getting my oil changed tomorrow! Thanks again!!!!!!!!

It is dyed purple so that GM can tell if you are using their super special stuff. And, no you cannot officially use mobil-1 synthetic because it does't meet GMs specs - but everyone does anyway!

If you can use Mobil 1 then you should be able to use Royal Purple (spec's API GL-5 or GL-4 fluid). The good thing is it's purple so I won't think GM would ever know. Just other source. BTW It's the only fluids I run in my gassers, but have lots of friends that run it in thier D-Maxs, Cumming with no problems to date.

.................... If you have the skid plate package, beware that as a cruel joke, GM engineers decided the plate should be so protective (read big) as to catch the draining oil when it is anything but the initial full pour-out force of a full oil pan, so next time, I'll slightly jack the truck up from the front and passenger side (that corner needs to be the highest after jacking), because it took me a half hour to clean up the mess :( ..............................
I changed my fluids/oil yesterday. I changed my oil first discovering the "cruel joke". When I dropped the plate to change the front diff, I took my bench grinder to the "lip" where the oil drains. I took it down a good half inch, this will no longer be an issue! :D
The plate is a fairly thick but soft aluminum, a person could probably do it with a Dremel!

Should I change the front diff also on the initial change?

The oem synthetic fluid is the only thing that is approved to go in the rear differential. It costs $22 per quart mail order through gmdieseltech.com; I think it takes 4-5 quarts. It is dyed purple so that GM can tell if you are using their super special stuff. And, no you cannot officially use mobil-1 synthetic because it does't meet GMs specs - but everyone does anyway! :)

So, to answer your question - given the high cost of GM's synthetic gear oil - the dealer price isn't as bad as it might initially sound. Should be the cost of fluid + .5 hours of the tech's time.

- jeff

I don't have my manual in front of me, so this is from memory, but I thought the only diff. that they required you to use the GM fluid was in the quadrasteer rear diffs. The manual said "only" use GM part number blah blah for the quadrasteer, whereas it said 75w 90 synthetic and gave a part number, but omitted the word "only" (same kind of wording like they had on the engine oil spec line, etc., etc.).

:confused: So maybe I'm reading the manual wrong? Or wouldn't they include the word "only" if that was required? Inquiring minds want to know...

The oem synthetic fluid is the only thing that is approved to go in the rear differential.

You, are just Flat Wrong.

It is dyed purple so that GM can tell if you are using their super special stuff.

Strike TWO.

And, no you cannot officially use mobil-1 synthetic because it does't meet GMs specs...

Strike Three and Your OUT.


- jeff

Idahofox

Quick question.

I contacted my dealer today and got a quote of $129 to change the rear differential fluid. This seems a bit HIGH to me! What all is involved in this process (never done it before). And could I/should I just do it myself?

Also, I assume that the drain plug is that little do-hickey at the very bottom (underneath) of the pumpkin, but how do I remove it?

Thanks in advance!!!!!!!!

Check Here (http://dieselplace.com/forum/showthread.php?t=38273), bunch of Bad Dope on this Thread.

Have a question, do a "Search", you'll have Lots of reading. Then judge for your self.

Idahofox

GM has their own spec for the rear axle lubricant. In the manual it lists...

...meeting GM Specification 9986115

There is no mention of any other specification (gl-5, etc.)

Mobil-1 does not meet the GM spec - it does meet gl-5. As of about 9 months ago, I didn't know of anything but the oem synthetic fluid that did meet the GM specification listed above.

So, do you know of any other synthetic gear oils that meet GMs specification?

- jeff

GM has their own spec for the rear axle lubricant. In the manual it lists...

...meeting GM Specification 9986115

There is no mention of any other specification (gl-5, etc.)

Mobil-1 does not meet the GM spec - it does meet gl-5. As of about 9 months ago, I didn't know of anything but the oem synthetic fluid that did meet the GM specification listed above.

So, do you know of any other synthetic gear oils that meet GMs specification?

- jeff

The Manual also specify P/N 12378261 for use in the Rear Axle.

GM Service Bulletin No: 04-00-89-041, page 4, define P/N 12378261 as: SAE 75W-90 API, GL5, Synthitic axle lubricant.

Ya', so I guess I do ! ;)

Idahofox

The part number that you list is the "oem synthetic fluid" that I am referring to. It meets GL5 AND GM spec 9986115. As far as I know, this is the only 75w90 oil that meets GM spec 9986115 - which is called for on page 6-15 on my 2005 silverado owner's manual.

BTW, someone here called mobil and asked them if they could use mobil-1 synthetic gear oil in the eaton rear axle - the answer was no. Like I said before, "officially" mobil-1 shouldn't be used because it doesn't meet the gm spec listed in the manual - but everyone does anyway and it works just fine.

And yes, I was wrong about the color of the gear oil - it's not the color of grapes, it smells like grapes. I am slow to catch on - but I get it eventually... :)


- jeff

owned!:ro)

Did you read the Bulletin ?

Idahofox

What is the Content of the GM spec listed in the manual ?

Idahofox

Yeah, I read the bulletin and it's for a corvette...

In the 2005 owner's manual it states...

SAE 75W90 Synthetic Axle Lubricant (GM part number U.S. 12378261, in Canada 10953455) meeting GM specification 9986115.

I am done talkin' about this - I sure hope you are too...



- jeff

Yeah, I read the bulletin and it's for a corvette...

In the 2005 owner's manual it states...

SAE 75W90 Synthetic Axle Lubricant (GM part number U.S. 12378261, in Canada 10953455) meeting GM specification 9986115.

I am done talkin' about this - I sure hope you are too...



- jeff

2003 Owners Manual:

SAE 75W90 Synthetic Axle Lubricant (GM part number U.S. 12378261, in Canada 10953455) or equivalent meeting GM specification 9986115.

You omitted an essential element of what the manuals Truly States.

No, I am not done. Your still Wrong.

You paraphrase, distort the truth and pass on Hearsay. Thats my observation.

Idahofox

2003 Owners Manual:

SAE 75W90 Synthetic Axle Lubricant (GM part number U.S. 12378261, in Canada 10953455) or equivalent meeting GM specification 9986115.

You omitted an essential element of what the manuals Truly States.

No, I am not done. Your still Wrong.

You paraphrase, distort the truth and pass on Hearsay. Thats my observation.

Idahofox

I am looking at my '05 manual - and I didn't omit anything. And I'll post the pdf - Either way, in essence they both state the same thing. The key phrase from the statement from your owners manual is "meeting GM specification 9986115".

So, according to your user's manual (and mine!) the gear oil must meet gm specification 9986115, which mobil-1 synthetic gear oil does not. Therefore, you cannot "officially" use mobil-1 synthetic gear oil.

What part of "meeting GM specification 9986115" do you think I am distorting?

So, back to the original question. Do you know of an non-gm oil (something other than the "grape juice") that meets GM specification 9986115?

- jeff

Look Dmax, you're confusing me with the facts here. Can't you see that I've already made up my mind? I've decided your [sic] wrong and that's all there is to it.

The Fox

:funnypost I'm so confused about my ID and my EGO. Which is what?

Just a ? but why is it necessary to do a diff. service with only 1000 miles did I mis something?

I am looking at my '05 manual - and I didn't omit anything. And I'll post the pdf

You omited the phrase " or equivalent ".

The key phrase from the statement from your owners manual is "meeting GM specification 9986115".

Do you have personal Knowledge of the Content of this specification, ( and it's revisions), I do not.

I do know that GM part # 12378261 does satisfy GM's specification and GM describes it as a GL5 synthetic lube.

So, according to your user's manual (and mine!) the gear oil must meet gm specification 9986115, which mobil-1 synthetic gear oil does not.

How can you say this as a Fact, you do not know what the GM specifications are.

What part of "meeting GM specification 9986115" do you think I am distorting?

That you can " Officially " substitute an " Equivalent " to GM part # 12378261.

So, back to the original question. Do you know of an non-gm oil (something other than the "grape juice") that meets GM specification 9986115?

No, but there may be some. Without knowing the content of said specification, that would be a tough call.

I do know several that are an " Equivalent " to GM part # 12378261.

- jeff

I could not care less what you do. However when you post bogus or misleading information I will comment.

There are others that rely on this information.

Idahofox

Just a ? but why is it necessary to do a diff. service with only 1000 miles did I mis something?

To remove casting and hobbing residue, trash.

Its a personal call, but Good Housekeeping.

Idahofox

Been running Mobil 1 75w-90 in my rear diff for about 70k miles. No problems! I'm getting ready to change it again.

Both my 2005 Sierra Manual and 2005 DMAX Suppliment state for Rear Axle:

SAE 75W-90 Synthetic Axle Lubricant (GM part No. U.S. 12378261, in Canada 10953455) meeting GM specification 9986115.

No mention of "equivilent." Maybe the 2003 books state something different.???:ro)

Both my 2005 Sierra Manual and 2005 DMAX Suppliment state for Rear Axle:

SAE 75W-90 Synthetic Axle Lubricant (GM part No. U.S. 12378261, in Canada 10953455) meeting GM specification 9986115.

No mention of "equivilent." Maybe the 2003 books state something different.???:ro)

They, the 03's Do, and so does the Helms manuals.

You make a decision, can you cross reference GM specification 9986115 and revisions, No.

Can you cross reference GM part No. 12378261, Yes.

You have made your decision, you run Amsoil.

Idahofox

When I went to the GM dealer for a qt. of diff. fluid, they gave me Mobil 1. Asked for the oem, the parts guy said thats all they use. AJ

I changed my diff fluid as per the recommendation here (unfortunately, I got to 3500 miles before I did the service). The fluid came out totally black, and the drain plug was covered with huge metal shavings.

I highly recommend doing this service sooner than later, at least for the first change.