Rear diff fluid

[Rocket Man]

those good for welding up a unit! otherwise good for scrap.

WTF?

 

[Tiredmechanic23]

WTF?

Trying to figure that one out myself and the one above him.

 

[George B]

Trying to figure that one out myself and the one above him.

I think he is referring to the munched up spider gears. Saying they are shot and either scrap or could be welded up to make a Lincoln Locker.

 

[Tiredmechanic23]

Ill try...
LOTS of heated debate and confusion out there about this. It doesn't help that GM used the G80 RPO code to designate both posi/limited slip differentials (on cars) AND Eaton Gov-Lock locking differentials (found on trucks).

My personal conclusion after spending around 10 hours on the subject reading forum conversations, phone calls, opinions and hypothesis's I could find, and like you said following those links further into there individual rabbit holes......

The G80 Gov-Lock does not require any friction modifier or additive.

GM considers any additive introduced into the G80-GL a contaminate that may cause the diff to fail by delaying the engagement of the locking mechanism (bad) and or causing chattering/shuttering (also bad).

While the Eaton G80 Gov-Lock does have differential clutch plates and works like a limited slip diff, it was not designed to need or use a friction modifier/ additive.
Several service bulletins from GM have been released on this matter.

BUT......

Upon calling a few local shops I found that most if not all of them still use an additive when replacing fluid in a G80 Gov-Loc.

When I asked why they said.... "because its a limited slip differential and that's what limited slip differentials take!"

furthermore, the internet is full of people claiming that they have used a additive in their G80GL and it works just fine.
So I call other lube shops, in other cities and states and received a motley assortment of answers but non that were definitive.



The best answer I got ended up being from an old friend of mine who I had called and left a message with. A regular at the racetrack, the old gear-head type...
He said....

"The reason people are not having problems when an additive is used, is because their not using the locking portion of the differential. Most of these people drive around to work and back and wouldn't know what "diff chatter" was if it bit them in the a$$.
Now people who actually USE their Gov-Locks locking feature, like those who 4x4 or have a heavy foot (especially on loose soil, gravel or snow),..."

He went on to explain that this diff locker works with RPM and the additive (just like the service bulletin said..) will keep the locker from engaging when its supposed to. When and if it DOES engage at a now higher RPM it was designed for... BOOM!

"You now have what has become known as the GM Gov-bomb."
"Run a 75/90 in the rear with no modifier and it'll be good to go!"

He also noted that the reason most "professionals" or lube techs say they run a additive in the G80 is because the "screen" tells them to. Somewhere along the line the confusion of the posi-track G80 RPO code is getting crossed with the Gov-Lock G80 RPO instructions....(imagine that) maybe even at the time the information was written into the system to begin with.

Sadly I knew all the older up to atleast 08 G80 Gov loc setups did not require the fluid but the shop I last worked at failed to listen. I worked for a major refinery here on forklifts and all company trucks. around 150 lifts and at least that in GM trucks ranging from 80s models to 2017s. Anything newer than 08 still went to dealer. Anyways every time I did rear end work I would request non additive fluid. Boss or parts guy would order it and get me additive included fluids or a separate tube of additive. I kept explaining it is not required and is bad to use. Always got the same answer "we have always used it and never had issues"... Hmmm maybe thats why we replace so many rear ends when they blow up.

But I did no know if things had changed on these newer models or not and wanted to be clear. I know exactly what I plan to use at this point and appreciate everyone's info.

I think he is referring to the munched up spider gears. Saying they are shot and either scrap or could be welded up to make a Lincoln Locker.

I see that now lol. That was my fault I missed a few post.

 

[HiHoeSilver]

I just did mine this weekend. I decided the same as @Rocket Man and used the Delco GL5.

 

[Jolly Roger]

How much differential noise is normal?
Im getting a whining noise at around 35-40 MPH now after the shop replaced the pinion gear. I dont remember what normal sounds like. Can anyone here actually hear there rear end through certain RPM ranges?

 

[JonnyTahoe]

How much differential noise is normal?
Im getting a whining noise at around 35-40 MPH now after the shop replaced the pinion gear. I dont remember what normal sounds like. Can anyone here actually hear there rear end through certain RPM ranges?

Mostly at highway steady speeds. 275k will do that.

 

[Jolly Roger]

Mostly at highway steady speeds. 275k will do that.

I hear a lot of diff noise at 70 MPH + but my Tahoe only has 74k on it.

 

[Dantheman1540]

I never hear any noise from my rear end except when the locker locks or unlocks at WOT.

 

[JonnyTahoe]

I never hear any noise from my rear end except when the locker locks or unlocks at WOT.

I don't have 400+ HP like you do. The only thing locking at Wide Open Throttle is my power door locks.