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

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

Jim,


Thank you for the information.


sfwarpath

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!http://www.dieselplace.com/forum/smileys/Big Smile.gif


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

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.

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.
>><<

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??? http://www.dieselplace.com/forum/smileys/Approve.gif


Bob

Try:


http://www.gmpartsdirect.com/


GM PART # 12378261
PRICE: $16.54


I use the stuff. Works good.


Johnny

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.

I splurged and used Royal Purple 75w90 on mine. It was about $7 a quart. It wasn't grape juice, but it was purple ! http://dieselplace.com/forum/smileys/Big%20Smile.gif

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.

I use Redline also.

http://www.uscom.com/~hoot/cars/duramax/gmc/mag-hytec/images/DSCN1163.jpg

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..

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"

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

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

The mobil 90-140 stuff.

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.

"""""""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""""""""""""


http://www.dieselplace.com/forum/smileys/Big Smile.gifhttp://www.dieselplace.com/forum/smileys/Big Smile.gifhttp://www.dieselplace.com/forum/smileys/Big Smile.gifhttp://www.dieselplace.com/forum/smileys/Big Smile.gifThat is FUNNY!!!!!http://www.dieselplace.com/forum/smileys/Clap.gifhttp://www.dieselplace.com/forum/smileys/Clap.gif

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

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.