GM specfication 9986115

[cmtndmax]

The manual (page7-27) says use 75W-90 synthetic axle lubricant. I am having trouble finding any products that say they meet this specfication. $26.00 a qt. at the dealer is hard to handle.

[Rebel_Horseman]

I bought my fluid form O'Reiley's. Napa should also have it or be able to get it. Castrol 75W-90 Full Synthetic Gear Lube is what I used.

Reb [><]

[FightinTXag]

Do a search for differential fluid or grape juice. This topic has been debated extensively as to whether our diffs really need the GM stuff or if GM is just trying to hose us. Personally, I used Mobil 1 Synthetic and have not had any chattering or other trouble.

TXDoc posted the following and it helped me decide to try Mobil 1 Syn.


From Mr. Ralph Holmquist of Eaton, the maker of the locking differential:
Under heavy duty trailer towing conditions the lube should be changed after the first 500 miles of towing. This is due to the extreme heat generated on break-in of the hypoid gear set.


"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.

[Fathead]

I purchased my "grape juice" at GMPartsDirect.com for about 18.50 a qt. Even with shipping and handling saved 60 bucks over what stealer was asking
FH smile.gif

Edit price is 16.07 qt.

[ 03-04-2003: Message edited by: Fathead ]</p>

[RKB'S HD]

Did extensive research on this.Tracked down that the dealer stuff was produced by Texaco it was sold under the name SYN STAR 75w-90.
Since then found out that somebody slurped up Texaco think it was Chevron at least there lube division? SYN STAR is still avail.but it is a different recipe they only kept the name.Shell Oil
got the recipe and it is sold under the name SPIRAX-S 75W-90.So this is the same stuff the dealer sells just under the GM name.
This info was collected from a gentelman at shell
Oil Co.Lubrications division smile.gif Hope this helps put to rest who makes what?

[pinehill]

RKB,

Great detective work!! Now someone will have to buy a quart of the Shell stuff to see if it also smells like grape juice. ;)

[roegs]

Here are the specs for the Shell lube. It does not say that it meets the GM specs. The msds sheet also says nothing about grape color or scent.

https://thegenesisnetwork.equilon.com/genesis/prodinfopdf/out/SPIRAX%20S.pdf

Here are some other links stating the Mobil 1 does not meet the GM specs. Seems Amzoil might, but I'm a little skeptical.

http://groups.google.com/groups?q=9986115&hl=en&lr=&ie=UTF-8&selm=3B32289E.A8946300%40galaxyinternet.net&rnum=2

[ 03-04-2003: Message edited by: roegs ]</p>

[peachin]

I do not have a locking rear differential. I felt it would be redundant to 4 X 4. My question is about changing the rear differential at 500 miles of heavy towing? Does it apply to both the locking rear differential and the non locking differential. I realize the lube is the same. But my owners manual does not say anything about 500 miles of towing - or am I missing something?

[dmaxalliTech]

We use BG products at our dealer and when I mentioned to the BG rep about changing my fluid at 5000 miles, He said to use his product, cost me 19 per quart. since i Bought new, he gave my written 250,000 mile warr on any lubricated rear axle component. All i had to do was supply him with a fluid sample from original fluid. Might be worth looking into...
see website at BGPROD.com

[RKB'S HD]

There is just one problem I can't find the Spirax oil anywhere?
Roegs. I had also spoken to a gentelman at Eaton
and he stated that the only spec to look out for was the GL-5 specification. Both the Spirax and the Mobil 1 have that spec. I would think all the grape juice color and smell is nothing but perfume and color, and has nothing to do with lubricating properties in the oil. The GM techs. were probably just whinning about that that bucket of dead fish smelling old fluid smile.gif So the guys at the plant sweetened the mix to make them happy ;)

[Fathead]

Someone once posted that the "grape juice" is so expensive that if you drip some on the floor you want to lick it up. I believe the grape additive is designed to make it more palatable.
FH smile.gif

[Mike Fultz]

My local dealer sold it to me for $22.00 a quart. I tow a 10000# race car trailer. I figured I am not changing the fluid often at all. I would bet most of us will sell/trade in our trucks before the rear end lubricant would need to be changed again. My truck is an 03 and is under warrenty. I don't want any hassle from GM on what fluid I use. I don't want to be in the position that i have to prove the magneson-moss warrenty act. So, I just used the GM fluid, kept the reciept just in case. To me its just not worth saving $40 if I have to have any hassle down the road.

Mike

[Idle_Chatter]

I had the stealer do both of my diffs after 500 miles of break-in and just before heading out on a 3,000 trip from Wisconsin to Texas and back. Charged me $280 for the fresh load of grape juice. At 23,150, I changed the rear lube myself and put in Amsoil 90W150 2000 synthetic. At 30,600 I put Amsoil 75W90 2000 synthetic in the front diff. I knew the 90W150 was a towing recommendation for the rear, but was worried about running it unloaded and at low winter temps, but has not been a problem. Any good synthetic lube is going to be fine for your diffs and still be a big savings over the inflated cost of the grape juice. Many members are running Mobil 1, Amsoil and Redline synthetics without a single report of problems that I've seen.

[roegs]

I've been following posts such as this for years. For some reason, nobody seems to make a product that matches the GM spec. I know a lot of folks just seem to add their favorite brand of synthetic gear lube, and it seems to work fine for them. Guess I'm still a little skeptical, and think that there may be something extra in GM's. If its (GM's) just plain synthetic lube, why won't any of the other companies commit to meeting GM's spec? After spending $35k on this truck, I'm not about to skimp on $40 for a one time lube change. I do a lot of towing, and I guess the peace of mind is worth it to me. Just my thoughts though...

[Silver Bullet]

I am running...

Valvoline Durablend Synthetic SAE 80W-90 (front)
Mobil 1 Synthetic SAE 75W-90 (rear)

I have not had any problems with the diffs since changing. I found both at AutoZone.

[mike.morris]

Someone please clarify. I researched this for my '99 silverado and thought that the Mobil 1 synthetic 75W90 met the GM spec. Has GM changed the spec on the 75W90 synthetic, or did I miss something??

[cmtndmax]

This is the reply I got from Shell. Spirax S 75-90 has a slightly higher viscosity than GM 9986115. The
viscosity of Spirax S 75W-90 at 40C is approximately 126 centistokes,
while
9986115 has a typical viscosity of 98 centistokes at 40C. Spirax S
75W-90
does not meet GM 9986115.

Thank you for your interest in Shell products.

Richard Moore
Staff Engineer
Shell Global Solutions (US) Inc.
Westhollow Technology Center, 3333 Highway 6 South, Houston, TX
77082-3101,
United States of America
1-800-782-7852 option

[Lone Eagle]

This topic has been beat to death. All this boils down to two points. If you are worried about warrantee issues, use the OEM oil. For all others, use any brand name oil that meets the GL-5 spec. Later! Lone Eagle ;)

[huntindog]

Can anyone tell me what page in the manuel, that the diff fluid change interval is stated????