Snaggle and LDM
I want to politely say that you are both wrong.
Without any doubt, the Gov-Lock system needs some FM in the lube. That old GM spec is "9986115". Google it and you'll find a bazillion discussions on it.
The confusion over this topic comes from old intel that is probably 15 years back or more. There was a statement out from GM not to add FM to their GM differential oils. Those lubes were called "grape juice" by many because of the pleasant odor they had. Anyway, the statement of not adding FM to the lube was because the GM lube already has FM in it, and adding "more" to it can cause the clutches too slip to easily, and not function properly by not applying the proper amount of intended torque bias through the clutch pack.
- the confusion comes from people misinterpreting GMs position.
GM states to not "add" any FM to the 9986115 lube. That does not mean no FM exists in the fluid. It means there's already some in there, and so don't add "more" to the lube.
- the reason they don't want "more" FM in there is because too much FM has an effect of making the clutches slip too easily, and it will reduce the torque bias via clutches that won't transmit torque as effectively when the ramp tightens in the "locker".
- The G-80 is not a "locker" in the traditional sense (like a Detroit Locker). The Gov-Lock uses a clutch pack activated by a spinning flyweight to run up a ramp and put pressure on the clutch pack. IT NEEDS FM for the clutch pack to work properly.
I did a LOT of research on this topic way back in the day. Somewhere floating around the 'net is a statement from an Eaton engineer, specifically stating that the Gov-Lock unit DOES NEED some L/S FM additive to operate properly.
Here is the Eaton promo video:
in this video they call the clutch pack the "active disc pack"; it has friction plates (clutches !!!!!!)
In fact, the "active disc pack" is pretty much like any wet-clutch assembly found in a modern multi-plate motorcycle clutch pack.
Here's EATONs webpage on the M-locker (their name for GM's Gov-Locker)
In this web info you'll see they accurately call this a "light-bias limited slip" unit.
Allow me to quote their own words ....
"
The stopped flyweight triggers a self-energizing clutch system, forcing a cam plate to ramp against a side gear."
That's right, they call it what it is ... a "
clutch system".
Those clutches need FM to work properly so they don't get nuisance grabbing events.
GM puts FM in their 9986115 fluid. So they say "don't add FM" because it's already in their product you'd buy from the parts guy at the GM dealership.
Don't assume the words "don't add friction modifier" mean the same as "there's no friction modifier in our lube at all'. Those two phrases do NOT mean the same thing, but unfortunately have become an urban legend myth.
Think of this topic not unlike Goldilocks and her porridge.
- having no FM at all will cause the clutches to grab too easily, and chatter, and cause nuisance locking
- having too much FM will cause the clutches to slip too easily, meaning the torque bias will be inadequate and traction will be lost
- having the right amount of FM will make the unit design as intended.
Most readily available GL-5 lubes which include some FM in them will suffice for servicing the G-80 Gov-Locker. If you experience some chatter, adding a tiny bit (a few oz's) of more FM will likely a alleviate the issue.
