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I went to the local GMC parts counter and wanted to purchase gear oil for my rear diff. They wanted $23 per quart!!! WOW! I passed on the purchase and wanted to get advice on which oil is the best? What gear oil should be used for the M80 locking rear diff? Do I need to add the limited slip additive to prevent chatter?


Thanks
 

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sfwarpath...Mobil 1 synthetic 75-90, takes about 4 quarts. Runs around 25 bucks and lasts a long time. No need to add anything.
 

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jbh2000 said:
sfwarpath...Mobil 1 synthetic 75-90, takes about 4 quarts. Runs around 25 bucks and lasts a long time. No need to add anything.

That's $25 -TOTAL, $6 per quart!



No additives, and any good synthetic gear lube will do as good or better job than the GM "grape juice" at its ripoff price!
 

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I replaced the oem stuff with Amsoil Series 2000 75W-90 synthetic, and my locking differential is much smoother than it was before the change. This was at 10k, and no additive. Retail list $9.20 qt.
 

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sfwarpath said:
I went to the local GMC parts counter and wanted to purchase gear oil for my rear diff. They wanted $23 per quart!!! WOW! I passed on the purchase and wanted to get advice on which oil is the best? What gear oil should be used for the M80 locking rear diff? Do I need to add the limited slip additive to prevent chatter?


Thanks
Conventional Wisdom sez, "Read The Fine Manual".
I read mine, it didn't recommend a change of the rear end fluid, I changed it anyway.
>><<
 

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I changed mine to Mobil 1 75w-90 as well. Autozone carries it as well as others, at 1/3 the price of the grape juice. GM can stuff the grape stuff up their arse....as well as their over priced fuel filters, oil filters.....must I continue???



Bob
 

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Uhhh, I think you need to use the grape juice and get it at the best price, try DMAXALLITECH,


Think warranty, warranty, warranty....only the grape juice is certified for the G-80 locker. Better safe than sorry, besides it was $29 a bottle not too long ago.


Do what ya gotta do, just be aware of the possible issues if something happens to that locker for any reason.
 

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I splurged and used Royal Purple 75w90 on mine. It was about $7 a quart. It wasn't grape juice, but it was purple !
 

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Been running redline 75w-90 for 45,000 of the past 50,000. No noise, no chatter, no heat issues. Time for another change this week as well as tranny fluid (tansynd is expensive, and I'm a dealer!) Oh well, a few bucks here makes for no worries when you want to go to the lake.
 

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I use Redline also.

 

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I use 80W-90 Valvoline Synthetic. Changed the original out at 30,000, the new has been in for about 21,000 miles, and it has been quiet, clean, and seems to run low temperature. I have had no problems. It is about 5.00 a quart at Advanced Auto Parts..
 

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I changed to mobil 1 at about 5000 miles, & boy was that magnet full of crap!

I can't believe that the manual reads like it does - the rear fluid should be changed & not just "checked"
 

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dropped mine at 1k miles put mobil 1 synthetic 75-90 in and got the ok from my stealer first...runs great pulling the heck out of my 9k 5r up vermont hills ..later, bc
 

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Does anyone think using the higher weight stuff would be a good idea?

The mobil 90-140 stuff.
 

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Chevysrus wrote:


Uhhh, I think you need to use the grape juice and get it at the best price, try DMAXALLITECH,


Think warranty, warranty, warranty....only the grape juice is certified for the G-80 locker. Better safe than sorry, besides it was $29 a bottle not too long ago.


Do what ya gotta do, just be aware of the possible issues if something happens to that locker for any reason.


Your kiddin me right? I suppose I had better always run that big black oil filter and that Racor fuel filter and those cheap GM shocks right? I had also always go to GM to have all of the above services performed right? I had better always buy my wiper fluid from GM right? Oh yea I had always better use GM grease to lube my zerks right? Better have GM do all of my alignments right? Hell, I should see if they will sell me some of that crappy coffe they serve in the waiting room so I can brew it at home. I wouldn't want to jepordize my warranty right? Lets use some common sense here. Big tires, big horsepower and alcohol in the fuel. The rest is hogwash! BTW mobil synthetic is GL-5 certified, that is all you need.
 

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"""""""Hell, I should see if they will sell me some of that crappy coffe they serve in the waiting room so I can brew it at home""""""""""""


That is FUNNY!!!!!
 

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Bronco said:
Chevysrus wrote:


Uhhh, I think you need to use the grape juice and get it at the best price, try DMAXALLITECH,


Think warranty, warranty, warranty....only the grape juice is certified for the G-80 locker. Better safe than sorry, besides it was $29 a bottle not too long ago.


Do what ya gotta do, just be aware of the possible issues if something happens to that locker for any reason.


Your kiddin me right? I suppose I had better always run that big black oil filter and that Racor fuel filter and those cheap GM shocks right? I had also always go to GM to have all of the above services performed right? I had better always buy my wiper fluid from GM right? Oh yea I had always better use GM grease to lube my zerks right? Better have GM do all of my alignments right? Hell, I should see if they will sell me some of that crappy coffe they serve in the waiting room so I can brew it at home. I wouldn't want to jepordize my warranty right? Lets use some common sense here. Big tires, big horsepower and alcohol in the fuel. The rest is hogwash! BTW mobil synthetic is GL-5 certified, that is all you need.

My understanding is that the gm spec is not covered by any other available gear oil - I read elsewhere that someone contacted mobil-1 directly and asked if it was okay to use mobil-1 in our rear differential; The answer from mobil-1 was "No.".


At first I thought I only needed a synthetic GL-5 -> I stopped at gyppy lube after 5k miles and had the rear changed out - then I did more reading here and realized that the GL-5 they put in might affect my warranty on the rear axle. I stopped and bought 5 quarts of mobil-1 and then did even more reading and decided to go with the GM stuff; I went to the local dealership and Patrick (who posts here) put in 4 quarts of "grape juice" for me - wasn't cheap, but I won't worry about it for another 100k miles.


jeff
 

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It is just a standard limited slip differential. They have been making these things for at least 20 years. The owners manual states GL-5. GL-5 contains all of the additives required to allow your differential to perform correctly.
 
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