Differential Fluid Help

[JBTJ]

So I want to change the differential fluid in my 04. I have a partial print out of what it has. It states it has the G80 positraction limited slip diff with the GT4 3.73 gears. So I'd need to know do I add a friction modifier to the fluid? Or is their a brand I should use? I'm reading some say yes and some say no. I even found some web sites that say the G80 is a locking differential, which I know it's not.

What type of fluid should I use? Also, do I need a gasket or just use some RTV?

Thanks

Edit, to make things worse. I called 4 dealers close to me. They said that it's both a locker and posi track!!!! 2 of them said I need to add a friction modifier and 2 of them said I don't. Go figure. I gave me a p/n of 88900401 and said that's what they use.

 

[Goodinblack]

Posi track is a GM name brand

All Band Aids are bandages

Not all bandages are band aids

Use the Mobil synthetic version

It has modifier added already

 

[JBTJ]

Posi track is a GM name brand

All Band Aids are bandages

Not all bandages are band aids

Use the Mobil synthetic version

It has modifier added already

So the Mobil 1 LS GL-5 or the Valvoline FS is correct? Both are 75w-90

 

[El Capitan]

I use Royal Purple 75-140 and friction modifier.

I get a good deal with napa on it

 

[Sasquatch]

The G-80 is a locker. I use 75-90 royal purple.

But, This is from a GM bulletin on the subject.

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.

 

[Goodinblack]

I have a locking diff in my 2011 Yukon

Just used Mobil without any additional additive. No shudder

I did one time use cheap ass Walmart crap in a 2003 expedition
Chatter like you would not believe

Changed the fluid added additive and bam gone

 

[JBTJ]

The G-80 is a locker. I use 75-90 royal purple.

But, This is from a GM bulletin on the subject.

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.

This is what I'm finding now. Proplem is I can't seem to find any lube that does not have any FM in it other than Amsoil, which is a pain in the butt to get. Really hate to spend the $$$ for the GM grape juice stuff. What do you use? Thanks



---------- Post added at 06:32 PM ---------- Previous post was at 06:29 PM ----------

I have a locking diff in my 2011 Yukon

Just used Mobil without any additional additive. No shudder

I did one time use cheap ass Walmart crap in a 2003 expedition
Chatter like you would not believe

Changed the fluid added additive and bam gone

But the Mobil 1 stuff has FM in it. So you are saying that's okay, just don't add any more?

 

[Sasquatch]

I used mobil one for a while with zero noise or any problems. The same with the royal purple i have in there now. Just don`t add any additional friction modifier and you`re good to go.

 

[rockenthebowtie]

Cool thread... bulletins and experiences to back it up.. gotta say very informative and useful information

 

[Goodinblack]

Yes

 

[JBTJ]

Okay, thanks for the info. The Mobile 1 LS is plentiful and cheap. $7.99 so I'll use that. Still need to know what you guys use to seal the diff cover up with? Is there a gasket or just use some RTV?

 

[Goodinblack]

Maybe a basket already in it. Look close in between the cover and axle

 

[JBTJ]

Maybe a basket already in it. Look close in between the cover and axle

Doesn't that tear off when the cover is removed?

 

[Goodinblack]

Doesn't that tear off when the cover is removed?

Not if its reusable rubber covered stamped steel. I known for a fact 2009 + are. Don't know about the older ones. My 1996 had no basket. Only rtv

 

[rockenthebowtie]

Its best to replace gasket dont go with rtv.. gaskets are available

 

[01ssreda4]

I use a combination of a gasket and a very thin layer of ultra black rtv to both sides, works really well.

 

[Goodinblack]

Cork gaskeys suck they leak

BEST ones are steel rubber ones.

RTV is super tricky. Mating surfaces must be absolutely clean or otherwise it WILL leak.

Use brake cleaner if using only rtv.

 

[scottg918514]

Use Mobil 1 75w-90 syn or Royal Purple. No need to add friction mod.


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---------- Post added at 11:44 AM ---------- Previous post was at 11:42 AM ----------

Okay, thanks for the info. The Mobile 1 LS is plentiful and cheap. $7.99 so I'll use that. Still need to know what you guys use to seal the diff cover up with? Is there a gasket or just use some RTV?

There is a gasket. If urs doesn't have both drain/fill valves, u can suck old fluid out of fill valve and refill with hand pump. This way I don't have to take cover off.


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[El Capitan]

You can do either or Gasket or RTV the last time I pulled my cover to do axle seals I used RTV with no problems or leaks. I used a Gasket when I replaced my carrier with no problems or leaks but like scottg918514 said you have a FILL and A DRAIN valve on the differential that can be removed using a 3/8in ratchet and a Short 3/8in Extension.