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REAR DIFF CLARIFICATION !!!

Looking at the manual it says 75w-90 synthetic for the rear and 80w-90 for the front.
 
thanx Mike, i think i will change my rearend fluid this weekend. and change my cover as well. mine is starting to rust. noticed this yesterday as i was underneath washing the undercarriage and the inside of the wheels.
 
02_2500avalanche,,,

You must review your owner's manual for the GM specification... Not all Synthetic 75W-90 lubes are ok... Eaton requires a 500,000 mile drain interval lubricant for our G80 Locking diffs... The oem fluid in your G80 right now is Texaco Syn-Star...

I have seen so many folks on this board, and others, feel this personal need to change the gear lube in the rear diff... It's not necessary for a LOOONG time, and I am actually gonna start a thread in this section titled:

REAR DIFF CLARIFICATION !!!

http://www.chevyavalanchefanclub.com/cafcna/index.php?board=14;action=display;threadid=3621;start=0;

Guys, save the money on the rear diff, and read my new thread about this topic, please... I will post a link to it when I'm done writing it...

11H
 
To All,,,

After reading about many of folks' on this board changing the REAR DIFFERENTIAL fluid, I feel the need to start this thread to get the info to all of you...

GM recommends part # 12378261 for a rear diff fluid in the Avalanche... It is, for one about $30 a qt. ...

If you have a locking rear differential, otherwise known as the Eaton G80, or "automatic locking differential", your lube choice is critical!

Here is a quote from an engineer at EATON:

Automatic Locking Differential Lubricants. ? ?[Note from Michael Asmussen, Torque Control Products Division of Eaton Corp.] ?We recommend the following lubrications for our locking differentials:
1)Texaco 2276; Synthetic 75 W90; Gm Part # 9986115
2)Texaco 9622; Mineral based 80W90; GM Part # 9985290
3)Texaco 2080; Synthetic 75W140 (heavy duty applications); GM part # 9985991
Note - All of the above lubes are preblended with friction modifier. No additional modifiers are necessary or recommended. ?As far as other lubes are concerned, any standard GL 5 lube will work, but the units perform optimally with the three listed above.


The GM spec, 9986115 correlates to a Synthetic Lubricant of 75W-90 that carries the Eaton 500,000 mile drain interval requirement... This is know as the:

Eaton PS-163 (factory fill 500,000-mile drain) which I hear is now called the Dana SHAES-256 (which states 500,000 mile factory fill and 250,000 mile service fill)


Did you read that? 500,000 mile factory fill !!!


In short, Any 75W-90 that meets the PS-163 OR the revised "Eaton 500,000 factory fill or Meritor 750,000-mile extended warranty" specification, is good for use...

If you guys review your owner's manual, it only has a requirement that you CHECK the rear diff, and not change it... Even under the severe service section, it does NOT tell you to change it, just check it...

Another thing to be concerned with, is the level at which you fill the diff to... There is a plastic tag on the passenger side of the diff that tells you the recommended fill height ... I'm not for exact, but I think it states, between 60 and 140mm below the fill hole ... The G80 needs this level to operate properly! ...

2 Lubes I recommend in tandem with what Eaton recommends is:

Texaco Syn-Star 75W-90
Chevron RPM 75W-90
(Chevron IS Texaco now, so these might be identical)


Alternate:

Pennzoil Long Life Extended Warranty 75W-90
(stock # 100256)

Or you can buy the GM Goodwrench 12378261
($30 a qt roughly ... And is basically Texaco 75W-90 # 2276 as stated by Eaton above !)


So, considering the diff change is now just a "personal preference" and not a requirement, you can rest easy... I would leave well enough alone as long as you don't have any leaks... If you happen to come up with a leak, have GM fix it, and give you the spendy lube!!!

11H
 
? this 500,000 mile factory fill is as reassuring to me as the 100,000 mile spark plugs. ?maybe even the oil life monitor. ?i do not think so!
? even if people do decide to change their fluids or plugs before the recommended interval it's not going to hurt. ?we are talking about a $30,000-$40,000 investment here. ?people just want that added reassurance.
? as for GM's advice... :D:. ? i am not impressed. ?if you want to wait for the intervals then go right ahead. ?
? 11H, this in no way is directed towards you. ?only to the people at GM you really think that this is good advice to give. ?i honestly think that if you follow this advice you will eventually drive over your warranty coverage, in either miles or time, thus becoming a victim to the advice you followed. ?just my .02.
 
02_2500avalanche said:
does anyone know what weight diff fluid to put in? I plan on changing all my fluids over to synthetic. Thanks


Alex

The rear comes with synthetic fluid in it already.
 
The gear oil in these things should last quite a long time. ...I'm going to the clarification thread so I dont restate what has already been brought to the forum...


 
02-Z66,,,

I in no way neglect embracing preventative maintenance... To each their own... Personally, I will be chenging my rear diff lube at 50,000 miles when the transfer case is due... I was just letting you guys know the manufacturers recommendation... Take it with a grain of salt; that's fine... But when I see folks changing fluid at 10,000 or less, it's, I believe useless... I am not saying folks performing their own maintenance don't perform it properly, but I will say that pulling the cover, and cleaning the mating surfaces of the gasket can be an involved task... You risk getting contaminants into the housing, and also risk a leak if the gasket does not seal... The gaskets rely on themselves to be dry, and once they exhibit a leak, they are junk, and need to be replaced with a new one...

So in short, draining expensive fluid, pulling the cover, cleaning surfaces, re-applying diff cover, and filling to proper level is not difficult, but it opens the door to possible issues if not done perfectly...

The diffs we have are considered light duty in comparison to all consumer and commercial trucks... The fluids I list above, are used in some of the largest diffs available under much greater loads than our AV's can produce... These commercial, high load conditions in those types of vehicles are exponentially beyond what we will ever put the fluid through in the diffs of our trucks... But, again, the lubes in the commercial conditions are rated at the 500,000 factory fill spec...

I don't fault anyone for dumping their diffs, and doing frequent maintenance. but let's be honest, 10,000 to 15,000 miles is too early, and a waste of money... Not to mention opening a perfectly sealed differential, and possibly allowing foreign material into the housing while cleaning your mating surface... why? why?

Believe me, if Eaton is gonna stamp a 500,000 mile factory fill, and a 750,000 mile extended warranty seal of approval on a lube, then I'm sure our little AV diffs can tolerate 50,000 or better...

If you must change the fluid often, just drain it through the plug, and keep the cover intact ... Cleaning the magnet is an over rated objective... Gear sets wear, and spawl throughout their life, and the magnet safely contains the larger more damaging particles... If you pulled the cover every 20,000 you will see a normal build-up of fine wear metals that is normal... Even if you pull heavy loads regularly, the lubes have the EP additives to live a long service life... The days of cruddy mineral gear lube that needs frequent changing are over... And by the way, don't knock the oil life monitor... I have seen many oil sample wear metal tests ?that prove oil can last well beyond 3,000 miles... Oil analysis is a direct reflection of projected oil life... The truth is, GM sets limits on certain things, and incorporates the wear metal limits among others... The 10,000 mile interval is BEST CASE and I have never seen or heard of a light going that long... But, running a good GF-3 oil for 5,000 to 6,000 miles under normal service is fine... The LM7 is an extremely clean burning motor, and oils now are superb... Raw fuel, oxidation, and moisture is what kills an oil... The motors we have are so effecient, that the oils don't have to absorb what oils in 1980 were required to... In comparison, the rear diff lube has only 2 avenues of contamination... Moisture, and wear metals... That's it... No fuel, combustion contaminants, acids, yada, yada ... Diffs lubes don't get stressed like motor oil does...

If you want to be concerned about a lube change frequency component, be concerned about our AutoTrac transfer cases... They will be the first to fail as a result of contaminated fluid... The viscous clutch drops material continuously... I haven't heard anyone mention they changed their TC fluid as often as the rear diff for sure!

Here is a couple links to explain what these new lubes we use are, and what they accomplish:

http://www.pzlqs.com/Tech/Pdsheet/D...sion/Pdf/LongLifeExtendedWarrantyGearOils.pdf


http://library.cbest.chevron.com/lu...5f870014c4ab?OpenDocument&Highlight=0,75W-90*


I'm not trying to pick a fight here, but I just feel some of us have some pretty strong opinions about preventative maintenance, and cherish our investment... All I'm trying to poin out, is that 20 year old or even 10 year old wisdom is not always accurate, especially in this case... The fact that someone will pull a cover, and risk contamination at a mileage so low is beyond me... All it takes is a single 1/8" piece of gasket or rag to render the G80's locking function inoperable...

But, if you can be meticulate about your procedure, and want to pay $90 for lube, and go through the effort to do it right, by all means, have at it!

It's your $$$, and I can't tell you how to spend it...

11H


 
11H, we both voiced our idea of preventive maintenance with good opinions. so we will call it quits now. and as i said before... none of that was directed towards you. BTW, i do respect your opinion. as a matter of fact that is how i work on my wife's truck; when it is time according to the manufacturer. this gives me more time to work on my ride. ;D >:D ;D
 
as a matter of fact that is how i work on my wife's truck; ?when it is time according to the manufacturer. ?this gives me more time to work on my ride.

02-Z66,,,


You're a stinker, shame, shame, shame! ... Hope yer wife doesn't frequent this board ...

11H ... (... snickering ... ?>:D )
 
To All,,,

?
?As a "side thrust" of my post, I hope some of you picked up the fact that there are alternatives to the GM brand of lube that's nearly $30 a quart ... The Texaco Synthetic 75W-90 ?IS what's bottled in the GM container ... And the others I mention are also probably less expensive ...

GM is pretty sneaky at times about "who" makes their lubes ... They want to build in their mark-up I guess ... In this case, it has taken me a couple years to realize it was a Texaco product ... (Which is now Chevron all the way) ...

I am still trying to find out who makes the revised AUTO-TRAK II transfer case fluid ... Good thing THAT's reasonably priced !!!

11H
 
Well I don't have the work order in front of me with the breakdown but this is what I had done today and how much it cost total.....

1. Oil change (fully synthetic)
2. Chassis Lube
3. Rear Diff. oil changed (14,440k)
4. Avalanche Front graphic installed....

a whopping $240.00...for the whole deal including the hourly rate for them to work.... :B:
 
11H
I think another Item that is in the GRAY area is the fill to amount [you also stated 140mm---WOW]

If you look at how many members, [6-8 that I know of],
that have had differential or/or axle bearing failure--

this is a clear sign, that something is not right!!

Around 9K, I checked mine and was more than a pint low in the front and rear [ I was aware of GM's level specs]
I filled it to , slightly below top of hole---
test drove and checked for foaming, nothing

My personal ASE opinion is, I will take a blown seal, over a trashed differential any day.
 
after getting all this useful info from you guy's i think it would be a good idea to at least check my fluid level in the diff. ???
 
Capecruis8der,,,

I'm not sure of the spec ... I just might crawl under the av ... Ok, it's 15-40 mm below hole... Where did I get 140??? I wasn't sure as I stated before ...

Anyways, overfilling won't hurt, it will just not allow the speed sensing fly weights to wing-out and lock in the axles fully... In essence if you over fill, you will have a limited slip, and not a 200 rpm differentiated locker...

I'm not sure of the axle bearing failure being attributed to the low level... GM axle seals are notorious for leaks, and need to be checked at every oil change... I believe the fill hole is WELL enough above the centerline...

Another thing that will kill axle bearings is doing improper diff changes... The gasket you choose MUST be GM, because it provides inlet holes to the axle housings... Also, if gasket material like permatex is used, it too can fill these small inlets ... I have too seen guys use the wrong gaskets on these axles and the axle tube runs dry or short on lube... It is imperative these don't get covered up with the wrong gasket... If you buy the GM gasket, look for 2 holes in the center of the gasket in the 3 'o clock and 9 'o clock position ... When you hold it up to the diff housing, it should not cover the axle tube inlets... Other than those 2 issues, I think the GM bearings are fine... These guys that you know blew out bearings, ask them if they used an oem gasket or if their axle seals were leaking... I bet some were at least...

I pulled the rear end out of a 95 Impala SS, and the bearings were fried... We pulled the cover, and he used a Fel-Pro blue gasket without the cut outs ... He was pissed ... There actually were some GM vehicles here recently that had the wrong gaskets in them from the factory... I think they were pickups in the 90's ... Owners were seizing bearings up, and GM had perforated gaskets, but the holes were not punched out over the inlets... Nice huh?

11H
 
Sunday night I went to add some Militec to my rear end. ?First I checked the fluid level as I read post saying the rear ends have come low from the factory. ?The OM says it should be 5/8 to 1 5/8 inches from the bottom of the plug hole; I went 2 1/4 inches down and didn?t even hit fluid. ?I hoped that I might after adding 4 oz of Militec. ?

Due to the second exhaust pipe from my duals I lost some working space in this area and it?s a little tight. ?Even with my smallest funnel I couldn?t get an angle to pour in the Militec so I cut a 2 inch piece of rubber hose and put it on the end of the funnel. ? You guessed it, as soon as I started to pour in the Miltec the hose slipped off and disappeared into the rear end. ? :C: :C: :C: (It?s OK to laugh.)

I crossed my fingers and drained the rear end; luckily the hose also came out with the fluid. ?(y) ?I measured how much fluid came out and it was only 28 oz. ?The OM doesn?t list how much fluid the rear end holds. ?I drained the fluid into a clean pan and was getting ready to poor it back in when I noticed water in the fluid. ?Having live in New Orleans and Houston where street flooding is common and have had water in my fluids before so I wasn't going to reuse it.

The only synthetic I could find after 2 stops on a Sunday night was at O?Reilly?s. ?They had Castrol Oil Syntec 75-90 and its API Service GL-5 rated. ?This may not be the best for a Eaton auto lock put they do have it listed on their web site, it?s not in the 3 they recommend. ?? ? ?Any way after adding 2 16oz bottles of gear fluid and 4 oz of Militec it?s still not within 2 inches of the hole. ?:eek:

I?ll have to pickup another bottle tonight and see if that fills it up. ?
 
For someone who is not all that mechanically inclined, and never owned a 4WD vehicle before, do you recommend I be checking my own differential and transfer case fluid levels? Or should I take it to the dealer or a mechanic?

From what I've read, it doesn't sound that complicated, but I'm getting nervous hearing about blown seals, etc!
 
Johnny_D,,,

ROTFLMAO ...

Hey brother 2.25 QTS. should bring it up to a perfect level if you have the Eaton and 3.73 ... I have done many of these, (still giggling, can't type) and 2.25 is pretty uniform... I would put 2 oz. of Militec in... (Just because I think 4 oz. works on big industrial diffs. and they just say 4 for all diffs... Personally, I stick with the 1 oz per qt on motor, trans, and diffs... I think that is a sufficient treat ratio...

11H (still giggling)
 
midlifecrisis,,,

I can't give an answer to your question... I have no idea what you might be comfortable doing... The only trick to checking is some items have a specific lube type, and special fill - level ... The owner's manual covers it for the most part...

If you want to take it to a mechanic great, but I don't trust many mechanics, as they have not followed protocol in the past with my vehicles... This is not the norm, but were not workin' on daddy's 76 Ford anymore, and old school knowledge doesn't always apply anymore... So, choose your serviceman carefully...

If you don't mind getting under the truck, I would purchase a GM or Chilton SERVICE MANUAL and keep it for reference... If you like the Avalanche, you will get much gratification seeing it underneath, and knowing how to do basic maintenance... It's an interesting place under the AV ... It's actually fun when you get into it...

11H
 
This thread reminds me of the '96 SS I had. On the board for the Impala SS it stated that GM did not put a gasket with the weep holes that let the diff fluid get to the rear wheel bearings! Two diff guys were claiming to be in charge of there local police dept service and had seen a high number of rear wheel bearing and rear axel failure at around 60,000 miles or so. They started replacing the Diff gasket with a Fel-Pro and it had the weep holes. After much thought I changed mine and they were right, the GM gasket did not have them and the Fel-Pro did! I don't know if it helped or not as I traded it off 6 months later (MISTAKE) Anyway I hope my Avalanche has the weep holes that it needs to keep the bearings lubed!
 
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