Diff and T-Case Fluid Changes

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I am planning on changing the fluids in the front and rear diffs and the transfer case in the 'Burb. It currently has just over 130k miles and I do not believe any of those fluids have been changed, as the PO told me he stuck to the mfg service schedule, which only calls for checking those fluids, not replacing.

#1: The OM specs a synthetic 75W-90 lube meeting GM 9986115 for the rear diff. I did some poking around on BITOG and have decided to use a GL-5 fluid with LS additive and disregard the GM spec. Looking around online and locally, I have a lot of choices, with per-quart prices ranging from $10 (Valvoline SynPower) to $18 (RP), with Amsoil, RL, M1, Lucas, and Castrol falling between. Are there any performance reasons to choose one over the other or should I just go with the Valvoline due to price? Or should I "splurge" and spend nearly twice as much for the RP, seeing as I will not be replacing the fluid for another 50-100k miles?

#2: The front diff specs an 80W-90 (no mention of synthetic or LS additive), but can I use a synthetic 75W-90 with LS additive? I would like to simplify things as far as the number of types of fluid I have and limit the number of partial bottles of fluid in the garage.

#3: I plan on pulling the rear diff cover and cleaning the magnet, seeing as the gasket costs all of $5-6. However, the front diff cover gasket runs about $45. Should I pull the front diff cover, and, if so, do I need to replace the gasket, or is it reusable?

#4: Should I stick with the Auto-Trak II fluid in the transfer case? Looking around online, there is no direct aftermarket alternative and dealer prices on it aren't too bad.

Thanks in advance!
 
#1: There are reports in many places of people gaining mpg using Amsoil in their pumpkins, so that would be my vote.

RP is a good fluid, but not at twice the price. All the others are probably solid choices also.

#2: AFAIK a non LSD is not harmed by having LS fluid in it.

#3: Unsure about reusing gasket, with a $45(!) gasket I'd be inclined to drain it with the same tube that will be used to refill.

#4: Depends on your TC, but Amsoil should have a fluid that will work:

Originally Posted By: Amsoil website
Transfer Case,NVG 261/263......GLS [5]
Torque-Drive Synthetic Transmission Fluid (ATD1G)
Signature Series Multi-Vehicle Synthetic Automatic Transmission Fluid (ATF) (ATFQT)
Transfer Case,NVG 236/246......SLF [6]
No AMSOIL Product Recommendation
Transfer Case,NVG 149......GLS [5]
Torque-Drive Synthetic Transmission Fluid (ATD1G)
Signature Series Multi-Vehicle Synthetic Automatic Transmission Fluid (ATF) (ATFQT)


Amsoil website
 
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Originally Posted By: Kuato
#1: There are reports in many places of people gaining mpg using Amsoil in their pumpkins, so that would be my vote.

RP is a good fluid, but not at twice the price. All the others are probably solid choices also.

#2: AFAIK a non LSD is not harmed by having LS fluid in it.

#3: Unsure about reusing gasket, with a $45(!) gasket I'd be inclined to drain it with the same tube that will be used to refill.

#4: Depends on your TC, but Amsoil should have a fluid that will work:

Originally Posted By: Amsoil website
Transfer Case,NVG 261/263......GLS [5]
Torque-Drive Synthetic Transmission Fluid (ATD1G)
Signature Series Multi-Vehicle Synthetic Automatic Transmission Fluid (ATF) (ATFQT)
Transfer Case,NVG 236/246......SLF [6]
No AMSOIL Product Recommendation
Transfer Case,NVG 149......GLS [5]
Torque-Drive Synthetic Transmission Fluid (ATD1G)
Signature Series Multi-Vehicle Synthetic Automatic Transmission Fluid (ATF) (ATFQT)


Amsoil website

#1: Amsoil is looking like $70 before taxes and shipping, at $15/qt and $8 for LS additive. The Valvoline has the LS additive in it and I can pick it up locally, so Amsoil is right up there with RP as twice the price of the most affordable option.

#2: If I go with Amsoil, won't have to worry about LS as their gear oils do not contain such. It's weird that their product guide only recommends 75W-90 for the front diff but shows 80W-90 as an option for the rear.

#3:
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Seeing as I will probably only do it once, I may splurge on the gasket.

#4: It's an NVG 246, so no go on an Amsoil alternative.
 
Originally Posted By: NMBurb02
I am planning on changing the fluids in the front and rear diffs and the transfer case in the 'Burb. It currently has just over 130k miles and I do not believe any of those fluids have been changed, as the PO told me he stuck to the mfg service schedule, which only calls for checking those fluids, not replacing.

#1: The OM specs a synthetic 75W-90 lube meeting GM 9986115 for the rear diff. I did some poking around on BITOG and have decided to use a GL-5 fluid with LS additive and disregard the GM spec. Looking around online and locally, I have a lot of choices, with per-quart prices ranging from $10 (Valvoline SynPower) to $18 (RP), with Amsoil, RL, M1, Lucas, and Castrol falling between. Are there any performance reasons to choose one over the other or should I just go with the Valvoline due to price? Or should I "splurge" and spend nearly twice as much for the RP, seeing as I will not be replacing the fluid for another 50-100k miles?

#2: The front diff specs an 80W-90 (no mention of synthetic or LS additive), but can I use a synthetic 75W-90 with LS additive? I would like to simplify things as far as the number of types of fluid I have and limit the number of partial bottles of fluid in the garage.

#3: I plan on pulling the rear diff cover and cleaning the magnet, seeing as the gasket costs all of $5-6. However, the front diff cover gasket runs about $45. Should I pull the front diff cover, and, if so, do I need to replace the gasket, or is it reusable?

#4: Should I stick with the Auto-Trak II fluid in the transfer case? Looking around online, there is no direct aftermarket alternative and dealer prices on it aren't too bad.

Thanks in advance!


1 - Even if your diff doesn't spec any LS additive fluids like RP with it won't hurt anything as a rule. Never heard of any issues running it in GM trucks and SUV's that had stock internals. I ran RP MaxGear 75W90 in 2 Silverado's with G80's for example and it worked just fine even though no LS additive was called for. I have used RP MaxGear 75W90 to replace the GM stuff in other GM applications too and it worked fine there too. It is your call on what you spend. I feel the RP is worth the money( get it through AAP using coupon code P20 and it is just $14 a qt + any sales tax )but that is my opinion and yours may differ.

Question??? - Does your rear diff actually spec LS Additive? I can't tell from your posts if it does or not? In some it seems like you are just talking about using a fluid that has it even though you don't need it and then you talk about the cost of buying it if you use Amsoil? If your diff doesn't spec it don't add any. If it does try one of the fluids like RP MaxGear with it already in it, as is 1st, and see if it is enough before adding more.

2 - Absolutely I would run whatever 75W90 synthetic you go with in the front diff too. No, the LS additive won't hurt anything. I ran RP MaxGear in the front diff on those 2 Silverado's that called for 80W90 as well and it worked just fine.

3 - I wouldn't pull the front cover. Most likely it will be a royal pain to do in the truck. If not go for it.

4 - If your t-case calls for AutotrakII fluid you have no choice but to stick with it. There is no aftermarket option at all. It is a very unique fluid and nothing out there replaces it. Don't even try.
 
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Here's my advice, and the reasoning behind it ...

Front diff:
First you need to determine if the front diff has a vent cap, and if it does, which color the vent cap is (black or off-white). It should be on the driver side of the diff, above the drain plug. I say this because there was a fluid compatibility issue way back when your vehicle was made. However, this may not apply to your specific vehicle. You will have to determine if your vehicle would be effected. Here is a copy of the GM statement:

Document ID# 1548733

--------------------------------------------------------------------------------

Subject: Info - Use of Synthetic Front Axle Lubricant For 4WD Vehicles Sold in Cold Weather Climates #03-04-19-001B - (09/03/2004)

Models: 2002-2004 Chevrolet Avalanche 2500, Silverado 2500/3500, Suburban 2500

2002-2003 Chevrolet Silverado 1500HD

2002-2004 GMC Sierra 2500/3500, Yukon XL 2500

2002-2003 GMC Sierra 1500HD

with Four-Wheel Drive and 9.25" Front Axle Assemblies and Built Prior to April 1, 2004

--------------------------------------------------------------------------------

This bulletin is being revised to update vehicle applications, part numbers and fluid fill information. Please discard Corporate Bulletin Number 03-04-19-001A (Section 04 -- Driveline/Axle).

--------------------------------------------------------------------------------

Important: This bulletin is intended for vehicles sold in very cold weather climates, especially those in Alaska and certain regions of Canada.
Important: This bulletin DOES NOT apply to vehicles built after April 1, 2004. Vehicles referenced above that were built after April 1, 2004 were manufactured with front axles containing synthetic axle lubricant and do not need to have the front axle fluid inspected or changed.
Front axles in the above-listed vehicles built before April 1, 2004 are manufactured with mineral-oil base axle fluid. Because of the 9.25" front axle assembly's internal design characteristics, there may be insufficient lubrication flow at very low ambient temperatures (-24°C (-12°F) or below). This may contribute to premature pinion bearing wear if a vehicle is driven extensively in very low ambient temperatures.
Important: Please be certain that PDI personnel know to perform the drain/refill procedure all year round (not just in the cold weather months).
New vehicles that are expected to operate extensively in 4WD in temperatures below -24°C (-12°F) should have their front axle fluid drained and refilled with synthetic axle lubricant during PDI or before delivery to the first retail customer.
Follow the Front Drive Axle Lubricant Replacement procedure found in the Service Manual (SI Document ID #673354). It is not necessary to flush the front axle assembly. 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.
For vehicles that have the axle lubricant changed, the front axle vent hose connector assembly will need to be inspected.
Important: Front axle assemblies with a vent hose connector assembly that is white in color do not need to be changed.
If the vent hose connector is black in color, it will need to be changed so that the O-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 (SI Document ID #843184).
Parts Information
Part Number Description Qty
12378261 or 89021677
(Canadian P/N 10953455 or 89021678 ) Oil, Synthetic Gear 2
12479390 Connector, Axle Vent 1

Parts are currently available from GMSPO.
Warranty Information
For vehicles repaired under warranty, use:
Labor Operation Description Labor Time
*F0011 Fluid, Axle and Differential (Front) - Drain and Fill 0.5 hr
Add To Replace Front Axle Vent Hose Connector 0.1 hr
*This is a unique labor operation number for use only with this bulletin. This number will not be published in the Labor Time Guide.

Document ID# 1548733

Looking that document over, you can see that there was a seal (0-ring) compatibility issue with the GM synthetic lube additives. Essentially, they used the vent cap color as an external visual clue to help ID what seal material was used in the diff. So, if you have a black vent cap, and intent to use the GM syntehtic fluid, that would be a bad idea! However, I have no ability to tell you if OTHER brands of syn fluids would have that same issue; at this point, you'd be own your own. But note that this tech bullentin is for the use of syn fluids in UBER-COLD regions, and if you don't live in that type area, then you don't need a syn to begin with. Therefore, any decent dino fluid would work well. I would recommend either Valvoline High Performance or Mobil Mobilube, either of them in 80w-90. That is because they both pass the very strict performance testing in SAE J2360 of GL-5 gear oils, which is the cilvilian equivilant of the MIL spec fluids. They are going to be able to protect every bit as well as a syn in nearly any application expect stupid-cold areas. If you don't have caribu running outside your windown, this probably will not be a concern for you. I generally would agree that a syn would be OK, but GM specifically has a note warning against the use of their syn which certain seals, so be forewarned. If you have a white cap, then any syn would be OK. If you don't have a white cap, I'd stick with a dino fluid, as mentioned.





Rear diff:
GM's fluid spec (9986115) is merely a designation of a syn 75w-90 with LS additive, and nothing more. There is a quote from a guy named Michael Torrenson (or something similar to that) who worked for Eaton, where he indicates that ANY GL-5 fluid will be OK for a GM G-80 diff, and the only concern is to make sure you use one with a LS additive, because the G-80 "locker" actually has a clutch engagement system. Just about any decent GL-5 lube will work here, but syn's are going to give you a longer OCI, so they might be worth the investment. Most of the syns, and some of the dinos, will have LS additive already included. Of note, the 80w-90 Valvoline does I know for sure, because I just put some in my Ford diff this weekend. If you live in super-hot areas, AND you town for the MAJORITY of the operational time, then I'd "upgrade" to a 85w-140. But ONLY if you meet BOTH of those criteria. If you don't, then use a 75w-90 syn or 80w-90 dino that meets SAE J2360. Adjust your OCI to your fluid type. If you have a G-80 locking diff (and most did) then you must use a LS compliant fluid. You will need to either buy a fluid with LS additive included, or put it in separately. Regardless of what others state, the G-80 does have clutches. They often mistakenly think that the "locker" is a mechanical type, but it is actually a pawl-operated clutch system. It has clutches. You need LS additive if you have a G-80.



Transfer case:
First, determine if you have an "Autotrak" transfer case; this is the one that automatically engages active traction control via locking and unlocking of the case. It is NOT the same thing as the simpler electronically shifted unit where the drive selects case mode. To be specific, they are both shifted electronically, but the difference is who decides when 4x4 is used; the driver or the computer. If you have an "Autotrak" x-fer case, you need to make sure to use an Autotrak compliant fluid. It's the blue colored GM fluid, and I'm not sure there are aftermarket options here. If you do not have an "Autotrak" t-case, then you can use any decent Dex/Merc ATF. Again, the use of syns here is going to get you a longer lifecycle on the drain interval. I would recommend a syn ATF such as Mobil 1 ATF, Amsoil ATF or ATD, etc and not have to change it for a LONG time. These ONLY apply if the case is NOT an Autotrack unit.



Hope that helps.
 
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Thanks, all.

NHHEMI, the rear diff does require LS additive, like dnewton states (it was one of his posts from a few years back that made me decide not to overspend on the GM fluid).

dnewton, thanks for the GM bulletin, but my Burb is a 1500 and is a California car, so it does not apply and I'll just use in the front diff whatever I end up choosing for the rear. It gets a bit hot here from time to time, but I do no towing, so I'll stick with the 75W-90.

Looks like I'll be leaving the front diff cover in place and using AUTO-TRAK II in the transfer case.
 
Originally Posted By: NMBurb02

#1: Amsoil is looking like $70 before taxes and shipping, at $15/qt and $8 for LS additive. The Valvoline has the LS additive in it and I can pick it up locally, so Amsoil is right up there with RP as twice the price of the most affordable option.



FWIW The price will come down if you become a preferred customer. Price on that page is for non preferred....
 
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