Differential Drain Plug
Instructor
Joined: Jan 2016
Posts: 226
Likes: 79
From: Boise, Id
I have not done mine yet. My 1995 FSM says to use SAE 80W-90 GL-5 with 4oz of Limited-Slip Differential Lubricant Additive (GM 1052358 or equivalent). I have looked at several videos of people doing the fluid change, and they seem to favor Royal Purple 75W-90 with the additive already in it. It is more difficult to find the 80W-90 with the additive already in it, so you would have to buy the 80W-90 and then get the additive separate. I plan on doing mine this fall and will have to do more research before I decide on what to use. I will keep an eye on this thread to see what people are using/recommend.
Advanced
Joined: Feb 2023
Posts: 65
Likes: 18
From: Aurora, CO
Agree with the Royal Purple that most seem to be using. While mine is in dry dock awaiting a trans I figure it's a good time to attend to this. Also see if my threads stick out as much as pictured above.
Melting Slicks
Joined: May 2019
Posts: 3,275
Likes: 1,419
From: Mid-Atlantic
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I have not done mine yet. My 1995 FSM says to use SAE 80W-90 GL-5 with 4oz of Limited-Slip Differential Lubricant Additive (GM 1052358 or equivalent). I have looked at several videos of people doing the fluid change, and they seem to favor Royal Purple 75W-90 with the additive already in it. It is more difficult to find the 80W-90 with the additive already in it, so you would have to buy the 80W-90 and then get the additive separate. I plan on doing mine this fall and will have to do more research before I decide on what to use. I will keep an eye on this thread to see what people are using/recommend.
But that's just me. Others may disagree...
Le Mans Master
Joined: Jul 2004
Posts: 6,229
Likes: 698
From: Clifton Park, NY ............Clearwater, FL ... 85 Original Owner
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Team Owner
Joined: Sep 2003
Posts: 25,414
Likes: 2,745
I don't believe this thought is valid! Can you maybe provide substantial information that might make it a valid concern? I doubt it!
Safety Car
Joined: Apr 2007
Posts: 4,129
Likes: 152
OP'er, recently changed out my rear diff fluid also, after cleaning and reinstalling plug noticed the red tag swung freely and had similar concerns but after a few drives no leaks.
On recommendation from here used Mobil 1 75w-90 with friction modifier already in it.
On recommendation from here used Mobil 1 75w-90 with friction modifier already in it.
Instructor
Joined: Mar 2021
Posts: 189
Likes: 73
From: Christiansburg Va
Those plugs are pipe thread which is tapered. The further in the tighter it gets. If you go too far it can crack the fitting that its screwing into. Just snug it up and check for leaks in a few days