Gear oil in a g80

[User_name]

I'm keeping this as short and sweet as possible,
First off I know that there's a ton of threads on this, which is my problem. There's so much conflicting Info on what gear oil I should put in my g80 diff.
1995 chevy c2500. 14 bolt semi float, nv4500, 5.7 tbi.
What oil do I use? My rpo codes are: GT4 (3.73), and g80

 

[Dropped88]

G80 takes plain 80w90. But under heavy use I'd recommend 75w140.

The g80 is a mechanical lockers it does NOT require a friction modifier

 

[454cid]

80w90 or the synthetic 75w90. GM switched in 99 and I don't see any reason why you couldn't run synthetic in a 98. I dont' bother though. I have 80w90 in my 99.

Don't add a friction modifier for a limited slip..... GM put out a TSB at one time saying not to add it.

 

[User_name]

Thanks guys. I see alot of conflicting Info about that. Any particular lubes you'd recommend?

 

[df2x4]

Per GM's TSB... GL5 80W90 with no friction modifiers. That last part can be difficult as many gear oils already contain them these days.

I use this in both of my G80 equipped '97s and have been for years now, ACDelco 10-4051. Both are still working properly, and this oil actually fixed one of them that was malfunctioning due to unnecessary friction modifiers in the previous fill.

www.amazon.com/gp/aw/d/B007Q10F3S

 

[Rocket Surgeon]

I have been looking at the same question.
I have two 14B FF.


How do you Identify what has a friction modifier?

Are their specific brands fluids that you may buy at local stores?
Are their specific brands NOT to buy at local stores?

Keep in mind I have two NV4500s, and the same issue exists with buying fluid... GL4 spec, but there appear to fluids that "meet spec" but would harm the fiber synchros. It seems AMSOIL has the only non stealership fluid I can get.

 

[df2x4]

How do you Identify what has a friction modifier?

Once again, this can be very difficult. From what I've seen, basically if the label doesn't declare that the oil is free of additives/modifiers, you can probably assume it has some. That ACDelco 10-4051 I linked to has this written on the side of the bottle.

"Does not contain a limited slip additive."

I understand the desire to find something cheap at a local store that will work... But considering how rarely the differential oil needs to be changed in these trucks I think it's well worth it to just order the correct fluid that's confirmed to work properly. Same deal with the GM fluid in the NV4500s. Why gamble?

 

[df2x4]

For anyone who wants more confirmation on the choice of oil for a G80, here's the GM TSB that's been mentioned. It's #91-4-109 for anyone who wants to Google it themselves.

"LOCKING DIFFERENTIAL LUBRICANT (SERVICE INFORMATION) #91-4-109
SUBJECT: LOCKING DIFFERENTIAL (G80) LUBRICANT - (SERVICE INFORMATION)
VEHICLES AFFECTED: ALL LIGHT TRUCKS EQUIPPED WITH G80 REAR AXLE ALL YEARS
Some light duty trucks equipped with locking rear axles (G80) may exhibit rear axle chatter, especially when turning a corner from a stop.
This condition of alternate engagement and disengagement of clutches in differential assembly is usually caused by contaminated axle lubricant.
To correct this condition, drain and refill the rear axle with SAE 80W-90 GL5 (P/N 10950849).

The use of any additive in locking rear axles (G80) is not recommended. Rear axle additives are designed for use in limited slip differentials which are normally installed in cars. All light duty trucks equipped with RPO G80 make use of a locking differential and the use of additives will delay the engagement of the locking mechanism and may decrease axle life.

VEHICLES/COMPONENTS INVOLVED: ------------------------- ---- Some light duty trucks equipped with locking rear axles, RPO G80.
SERVICE PARTS INFORMATION:
Part Number Description ----------- ------------------ 10950849 Lubricant, Rear Axle (1 litre)
Parts are currently available through CANSPO.
WARRANTY INFORMATION:
As specified in Light Duty Truck Maintenance Schedules, locking rear axle fluid drain and refill is required owner maintenance at the first engine oil change. Failure to drain and refill the rear axle as specified may contribute to a later axle chatter condition. Refer to the appropriate Light Duty Truck Maintenance Schedule or service manual, section OB, for further details on change intervals.
General Motors bulletins are intended for use by professional technicians, not a "do-it-yourselfer". They are written to inform those technicians of conditions that may occur on some vehicles, or to provide information that could assist in the proper service of a vehicle. Properly trained technicians have the equipment, tools, safety instructions and know-how to do a job properly and safely. If a condition is described, do not assume that the bulletin applies to your vehicle, or that your vehicle will have that condition. See a General Motors dealer servicing your brand of General Motors vehicle for information on whether your vehicle may benefit from the information.
© Copyright General Motors Corporation. All Rights Reserved."

Note that the part numbers for the oil suggested in this TSB have all been discontinued, but the ACDelco 10-4051 I linked to earlier is the closest match that I've been able to find that's currently in production.

 

[User_name]

I have been looking at the same question.
I have two 14B FF.


How do you Identify what has a friction modifier?

Are their specific brands fluids that you may buy at local stores?
Are their specific brands NOT to buy at local stores?

Keep in mind I have two NV4500s, and the same issue exists with buying fluid... GL4 spec, but there appear to fluids that "meet spec" but would harm the fiber synchros. It seems AMSOIL has the only non stealership fluid I can get.

I use redline mt85 in my nv4500 with great results

 

[454cid]

I have a combination of gear oil from TSC and and some super old stuff from under my uncles work bench in my 14bff. I don't have the G80 locker, but if I did, I think I'd be fine with the same oil.

The thing with gear oil, is the manufacturers want to sell it, so reading the back they make it sound like it's the best for everything including your coffee. Read carefully..... if they say it's ok/good for a limited slip, but recommend a friction modifier, it must not have one in it already, so it would be ok for your locker.

Personally, I wouln't buy the AC Delco stuff.... too expansive for what it is. I'd go for a brand that's more commercial/farm/standard-replacement oriented and not whiz-bang/hot-rod/performance marketed. So I'd look at TSC again, or see what Walmart/Meijer had to offer in their store brand.

Keep in mind I have two NV4500s, and the same issue exists with buying fluid... GL4 spec, but there appear to fluids that "meet spec" but would harm the fiber synchros. It seems AMSOIL has the only non stealership fluid I can get.

I think the Chrysler stuff is best/easiest to get..... I think I read GM discontinued it, and the Castrol is impossible to find? Check Someotherguy's posts on the subject.