dnewton3
Staff member
Yes, but that statement you put in red is misleading, as I already mentioned. It's not the first time GM has had an ambiguous TSB out there, after all ...
Look at your quote, where it speaks to what fluid to use:
'drain and refill the differential with new synthetic fluid, use the fluid part number listed in SI for the vehicle currently being worked on ..."
For most (not all) GM applications their 75w-90 syn is the recommended fluid, which meets GM specification 9986115. This spec is the corporate call-out of 75w-90 synthetic GL5 lube PLUS friction modifier, as made available for over the parts counter sales. The GM fluid is often called "grape juice" because it somewhat has that odor. The Amsoil link I showed CLEARLY describes the rationale of this formula, as well as how this differs from the factory fill, which is the lube and FM spec'd separately. Additionally, the quote from the Eaton rep specifically describes how the Texaco lubes made to GM spec have the FM in them; all three of them.
GM's approach is that if there is slippage, chatter or nuisance locking issue they'd rather see the diff drained and filled with more of their expensive lube meeting 9986115 (the OTC recipe for 75w-90 syn + FM). The "Gov-Lok" (M-locker) Eaton most certainly needs FM, but if you are using a fluid that already contains FM, you should not blindly dump more in there. Too much is as bad as too little. GM does not want you "add" more where enough already exists in their opinion. If you have issues, they want you to dump the fluid and start over, using their pricy "grape juice".
Get it?
Look at your quote, where it speaks to what fluid to use:
'drain and refill the differential with new synthetic fluid, use the fluid part number listed in SI for the vehicle currently being worked on ..."
For most (not all) GM applications their 75w-90 syn is the recommended fluid, which meets GM specification 9986115. This spec is the corporate call-out of 75w-90 synthetic GL5 lube PLUS friction modifier, as made available for over the parts counter sales. The GM fluid is often called "grape juice" because it somewhat has that odor. The Amsoil link I showed CLEARLY describes the rationale of this formula, as well as how this differs from the factory fill, which is the lube and FM spec'd separately. Additionally, the quote from the Eaton rep specifically describes how the Texaco lubes made to GM spec have the FM in them; all three of them.
GM's approach is that if there is slippage, chatter or nuisance locking issue they'd rather see the diff drained and filled with more of their expensive lube meeting 9986115 (the OTC recipe for 75w-90 syn + FM). The "Gov-Lok" (M-locker) Eaton most certainly needs FM, but if you are using a fluid that already contains FM, you should not blindly dump more in there. Too much is as bad as too little. GM does not want you "add" more where enough already exists in their opinion. If you have issues, they want you to dump the fluid and start over, using their pricy "grape juice".
Get it?
