I'm in the process of getting the GN back on the road. Going to change the differential oil. With some new mods, I should be pushing 680ish lbs of torque to the nearly stock rear with Eaton posi. I'm leaning towards an Amsoil product. What would be a good oil? Since I'm converting to a TH400, it won't see much sustained freeway driving. I don't care if it's synthetic or dino, I just want the best.
What diff oil for 8.5" 10 bolt?
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If Amsoil, the Severe Gear would be the best product for this application. 75W-90 or maybe the 75W-110 if you are going to make the rear end work hard.
I use the Severe Gear in my CTS LSD and in my GMC truck locker.
There is a guy not far from with a GN sitting in his garage. Keeps saying he is going to put it back on the road but its still sitting. Can't afford it I guess, wife & kids and has to drive company car servicing credit card account processing. Tried many times to buy and but I think he is hanging on to his past and would rather let it sit. Been about 10 yrs now not moved.
I use the Severe Gear in my CTS LSD and in my GMC truck locker.
There is a guy not far from with a GN sitting in his garage. Keeps saying he is going to put it back on the road but its still sitting. Can't afford it I guess, wife & kids and has to drive company car servicing credit card account processing. Tried many times to buy and but I think he is hanging on to his past and would rather let it sit. Been about 10 yrs now not moved.
From what I've experienced synthetic gear oil is too slippery for the clutch style LSD units. Eaton specficially states not to use synthetic oil for their LSD units. I've never had an issue using the standard valvoline 80w90 gear oil, neither has my fiancee's dad who uses it in his Ford 9" in their 9 sec Monte Carlo 
Here we go again with this "synthetic is too slippery" myth.
The first car I put synthetic gear lube in was a new 1977 Monte Carlo with a LSD. I ordered the car with LSD as I did with all my cars and trucks. I drove that car over 100,000 miles with just one fill of Amsoil synthetic gear lube. Btw, the Monte had a Eaton, GM's preferred supplier since the 60's. Every RWD car I have ever owned since then has has a LSD (81 Olds Cutlass, 84 Olds 88 all went over 100,000 miles on the sythetic) and every one got the Amsoil synthetic gear lube. So I am talking from years of experience. I also has it in my 2002 Trans Am Thorsen LSD.
While the guys at Eaton may say not to use it, GM has been factory filling them all since about 2000 with synthetic gear lube and requires Synthetic gear lube for warranty. My 2005 CTS has LSD, it came with synthetic and has Amsoil synthetic in it now. What do they have to say about that?? GM is their largest customer.
So, this myth that synthetic is too slippery is just that, a myth. I have been using it for 30 yrs, and not once in those 30 yrs have I had so much as a seal leak in any rear axle on my vehicles.
From my CTS owners manual
Quote:
Usage Fluid/Lubricant
Rear Axle
(Limited-Slip Differential)
SAE 75W-90 Synthetic Axle
Lubricant (GM Part No. U.S.
12378261, in Canada 10953455)
meeting GM Specification 9986115.
With a complete drain and refill add
4 ounces (118 ml) of Limited-Slip
Axle Lubricant Additive (GM Part
No. U.S. 1052358, in Canada
992694) where required.
See Rear Axle on page 5-48
The first car I put synthetic gear lube in was a new 1977 Monte Carlo with a LSD. I ordered the car with LSD as I did with all my cars and trucks. I drove that car over 100,000 miles with just one fill of Amsoil synthetic gear lube. Btw, the Monte had a Eaton, GM's preferred supplier since the 60's. Every RWD car I have ever owned since then has has a LSD (81 Olds Cutlass, 84 Olds 88 all went over 100,000 miles on the sythetic) and every one got the Amsoil synthetic gear lube. So I am talking from years of experience. I also has it in my 2002 Trans Am Thorsen LSD.
While the guys at Eaton may say not to use it, GM has been factory filling them all since about 2000 with synthetic gear lube and requires Synthetic gear lube for warranty. My 2005 CTS has LSD, it came with synthetic and has Amsoil synthetic in it now. What do they have to say about that?? GM is their largest customer.
So, this myth that synthetic is too slippery is just that, a myth. I have been using it for 30 yrs, and not once in those 30 yrs have I had so much as a seal leak in any rear axle on my vehicles.
From my CTS owners manual
Quote:
Usage Fluid/Lubricant
Rear Axle
(Limited-Slip Differential)
SAE 75W-90 Synthetic Axle
Lubricant (GM Part No. U.S.
12378261, in Canada 10953455)
meeting GM Specification 9986115.
With a complete drain and refill add
4 ounces (118 ml) of Limited-Slip
Axle Lubricant Additive (GM Part
No. U.S. 1052358, in Canada
992694) where required.
See Rear Axle on page 5-48
MolaKule
Staff member
Oh no.
The CTS Owner's Manual says to add four (4) ounces of Limited Slip Axle Lubricant Additive .
The CTS Owner's Manual says to add four (4) ounces of Limited Slip Axle Lubricant Additive .
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How about Royal Purple gear oil. I remember the bottle mentions it has friction modifiers for clutch and cone type differentials.
Last edited by a moderator:
Either SVT 75W-110 or SVO 75W-140 and the minimum amount of LS additive.
Originally Posted By: MolaKule
Oh no.
The CTS Owner's Manual says to add four (4) ounces of Limited Slip Axle Lubricant Additive .
They have had a big diff chatter issue with the CTS & Corvettes so the can of LS is the fix for those axles. I use the grape juice in my 06 LS YukonXl Denali. No additive needed. FWIW you can usually find the GM syn lube on ebay for less than 1/2 of what the dealers get.
Oh no.
The CTS Owner's Manual says to add four (4) ounces of Limited Slip Axle Lubricant Additive .
They have had a big diff chatter issue with the CTS & Corvettes so the can of LS is the fix for those axles. I use the grape juice in my 06 LS YukonXl Denali. No additive needed. FWIW you can usually find the GM syn lube on ebay for less than 1/2 of what the dealers get.
Originally Posted By: Pablo
Either SVT 75W-110 or SVO 75W-140 and the minimum amount of LS additive.
75w110 with 4 oz of additive should be the ideal lubricant for that diff. I doubt if he would need the additive. IMO. Plus he will never wear out the amsoil. But if he wants to be sure throw the additive in there for the heck of it.
Either SVT 75W-110 or SVO 75W-140 and the minimum amount of LS additive.
75w110 with 4 oz of additive should be the ideal lubricant for that diff. I doubt if he would need the additive. IMO. Plus he will never wear out the amsoil. But if he wants to be sure throw the additive in there for the heck of it.
Originally Posted By: PT1
They have had a big diff chatter issue with the CTS & Corvettes so the can of LS is the fix for those axles. I use the grape juice in my 06 LS YukonXl Denali. No additive needed. FWIW you can usually find the GM syn lube on ebay for less than 1/2 of what the dealers get.
I have absolutely no chatter issue with my 2005 CTS or with my 2008 GMC, nor did I with my 99, 01,04 GMC's or my LS1 WS6 using Amsoil. There is no additives in mine. I always have the dealer changed my gear lubes very soon as I get it. Both the car and truck it was in before 1,000 miles on them.
But you know, back in 1970 my Chevelle LS5 SS454 had chatter so its nothing new with limited slip differentials. Its always been a characteristic of LSD when the lubricant gets worn out.
The GM OEM gear lube are not very good, its high priced mediocre stuff. I don't know if Texaco is still the source but it used to be. I saw that mentioned in a TSB years ago.
They have had a big diff chatter issue with the CTS & Corvettes so the can of LS is the fix for those axles. I use the grape juice in my 06 LS YukonXl Denali. No additive needed. FWIW you can usually find the GM syn lube on ebay for less than 1/2 of what the dealers get.
I have absolutely no chatter issue with my 2005 CTS or with my 2008 GMC, nor did I with my 99, 01,04 GMC's or my LS1 WS6 using Amsoil. There is no additives in mine. I always have the dealer changed my gear lubes very soon as I get it. Both the car and truck it was in before 1,000 miles on them.
But you know, back in 1970 my Chevelle LS5 SS454 had chatter so its nothing new with limited slip differentials. Its always been a characteristic of LSD when the lubricant gets worn out.
The GM OEM gear lube are not very good, its high priced mediocre stuff. I don't know if Texaco is still the source but it used to be. I saw that mentioned in a TSB years ago.
Originally Posted By: Mike_dup1
Here we go again with this "synthetic is too slippery" myth.
The first car I put synthetic gear lube in was a new 1977 Monte Carlo with a LSD. I ordered the car with LSD as I did with all my cars and trucks. I drove that car over 100,000 miles with just one fill of Amsoil synthetic gear lube. Btw, the Monte had a Eaton, GM's preferred supplier since the 60's. Every RWD car I have ever owned since then has has a LSD (81 Olds Cutlass, 84 Olds 88 all went over 100,000 miles on the sythetic) and every one got the Amsoil synthetic gear lube. So I am talking from years of experience. I also has it in my 2002 Trans Am Thorsen LSD.
While the guys at Eaton may say not to use it, GM has been factory filling them all since about 2000 with synthetic gear lube and requires Synthetic gear lube for warranty. My 2005 CTS has LSD, it came with synthetic and has Amsoil synthetic in it now. What do they have to say about that?? GM is their largest customer.
So, this myth that synthetic is too slippery is just that, a myth. I have been using it for 30 yrs, and not once in those 30 yrs have I had so much as a seal leak in any rear axle on my vehicles.
From my CTS owners manual
Quote:
Usage Fluid/Lubricant
Rear Axle
(Limited-Slip Differential)
SAE 75W-90 Synthetic Axle
Lubricant (GM Part No. U.S.
12378261, in Canada 10953455)
meeting GM Specification 9986115.
With a complete drain and refill add
4 ounces (118 ml) of Limited-Slip
Axle Lubricant Additive (GM Part
No. U.S. 1052358, in Canada
992694) where required.
See Rear Axle on page 5-48
Mike, I wasn't expressing that I believe it to be true, but a lot of people who've run the 8.5" 10 Bolt Eaton LSDs have experienced issues running synthetic. I'm not refering to any kind of leak, but proper clutch operation. They go back to conventional oil with the additive, and their LSD worked like it should.
BuickGN,
Auburn was the stock LSD provider for the B-cars in the 90s, 8.5 10 bolt. They were cone style clutches. I don't think anyone's had issues with the cone clutches and synthetic oil.
Here we go again with this "synthetic is too slippery" myth.
The first car I put synthetic gear lube in was a new 1977 Monte Carlo with a LSD. I ordered the car with LSD as I did with all my cars and trucks. I drove that car over 100,000 miles with just one fill of Amsoil synthetic gear lube. Btw, the Monte had a Eaton, GM's preferred supplier since the 60's. Every RWD car I have ever owned since then has has a LSD (81 Olds Cutlass, 84 Olds 88 all went over 100,000 miles on the sythetic) and every one got the Amsoil synthetic gear lube. So I am talking from years of experience. I also has it in my 2002 Trans Am Thorsen LSD.
While the guys at Eaton may say not to use it, GM has been factory filling them all since about 2000 with synthetic gear lube and requires Synthetic gear lube for warranty. My 2005 CTS has LSD, it came with synthetic and has Amsoil synthetic in it now. What do they have to say about that?? GM is their largest customer.
So, this myth that synthetic is too slippery is just that, a myth. I have been using it for 30 yrs, and not once in those 30 yrs have I had so much as a seal leak in any rear axle on my vehicles.
From my CTS owners manual
Quote:
Usage Fluid/Lubricant
Rear Axle
(Limited-Slip Differential)
SAE 75W-90 Synthetic Axle
Lubricant (GM Part No. U.S.
12378261, in Canada 10953455)
meeting GM Specification 9986115.
With a complete drain and refill add
4 ounces (118 ml) of Limited-Slip
Axle Lubricant Additive (GM Part
No. U.S. 1052358, in Canada
992694) where required.
See Rear Axle on page 5-48
Mike, I wasn't expressing that I believe it to be true, but a lot of people who've run the 8.5" 10 Bolt Eaton LSDs have experienced issues running synthetic. I'm not refering to any kind of leak, but proper clutch operation. They go back to conventional oil with the additive, and their LSD worked like it should.
BuickGN,
Auburn was the stock LSD provider for the B-cars in the 90s, 8.5 10 bolt. They were cone style clutches. I don't think anyone's had issues with the cone clutches and synthetic oil.
Quote:
Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance.
Like it says Performs best
Eaton Posi units perform best when using GL4 (or better) mineral/petroleum based gear oil. A four ounce bottle of friction additive/modifier is also necessary for optimum performance.
Like it says Performs best
Eaton lockers need the 9986115. Plate LSDs like the Corvette uses used to require that same fluid but with the added FM. However now if you Google 'DEXRON LS' you will find the Corvette site and on there you will discover that someone has posted a TSB which introduces a new 75W-90 fluid with built in FM. The service part number for that oil is 8882624.
Originally Posted By: Mike_dup1
Originally Posted By: PT1
They have had a big diff chatter issue with the CTS & Corvettes so the can of LS is the fix for those axles. I use the grape juice in my 06 LS YukonXl Denali. No additive needed. FWIW you can usually find the GM syn lube on ebay for less than 1/2 of what the dealers get.
I have absolutely no chatter issue with my 2005 CTS or with my 2008 GMC, nor did I with my 99, 01,04 GMC's or my LS1 WS6 using Amsoil. There is no additives in mine. I always have the dealer changed my gear lubes very soon as I get it. Both the car and truck it was in before 1,000 miles on them.
But you know, back in 1970 my Chevelle LS5 SS454 had chatter so its nothing new with limited slip differentials. Its always been a characteristic of LSD when the lubricant gets worn out.
The GM OEM gear lube are not very good, its high priced mediocre stuff. I don't know if Texaco is still the source but it used to be. I saw that mentioned in a TSB years ago.
The GM syn grape scented gear lube tests very well according to amsoil. The chatter in the cts & corvettes generated many TSB's and even more angry owners.
Originally Posted By: PT1
They have had a big diff chatter issue with the CTS & Corvettes so the can of LS is the fix for those axles. I use the grape juice in my 06 LS YukonXl Denali. No additive needed. FWIW you can usually find the GM syn lube on ebay for less than 1/2 of what the dealers get.
I have absolutely no chatter issue with my 2005 CTS or with my 2008 GMC, nor did I with my 99, 01,04 GMC's or my LS1 WS6 using Amsoil. There is no additives in mine. I always have the dealer changed my gear lubes very soon as I get it. Both the car and truck it was in before 1,000 miles on them.
But you know, back in 1970 my Chevelle LS5 SS454 had chatter so its nothing new with limited slip differentials. Its always been a characteristic of LSD when the lubricant gets worn out.
The GM OEM gear lube are not very good, its high priced mediocre stuff. I don't know if Texaco is still the source but it used to be. I saw that mentioned in a TSB years ago.
The GM syn grape scented gear lube tests very well according to amsoil. The chatter in the cts & corvettes generated many TSB's and even more angry owners.
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