I got my new Mag Hy-Tec differential cover from Geno's for Fathers Day. Was gonna change it this weekend, called around, and got 50 different answers out of 10 different parts stores and dealerships!!!..
So what rear differential oil is everybody running?. I know whatever it is, it will be synthetic. I live in Texas, where the high ambient air temps are, and the truck has to pull in the heat.
Was gonna put Caterpillar 75/140 synthetic in it. But it only comes in 5 gallon drums and figures out to be about $11.00 a quart. That figures to $220 for the bucket, but its gonna take years to use it all.
Thinking either Mobil 1, Red-Line, or Royal Purple.....
I attempted to do a search, I know this subject has been beaten several times, but for some reason, my laptop wouldn't cooperate. Maybe it needs a rear end fluid change????...

 

I use Amsoil Severe Gear 75w90 synthetic in my front and rear diffs, and I love it.. The job was not a tough one, but I think if you are going to change it you ought to give severe gear a thought.

Scott

 

I changed mine out to Amsoil SVG 75W90 too. I think it costs about $7 a quart. Front diff took 3 quarts rear took 4. Don't know how much extra those mag hytecs hold but probably a case will do.

 

75-90 in front and 75-140 in rear

 

I went with the AMSOIL 75/110.... This seems like a great choice as I also live in the hot zone and I pull on the weekends between rodeos. It's a daily driver during the week. It protects MORE than 75/90 and not as thick as the 140

 

I use Royal Purple Max-Gear 75w90, don't tow heavy so it works fine for me.

 

Thanks for the responses.... According to the differential cover instructions, its gonna take approx. 8 quarts to fill the rear. Can't wait to put it on.... Give the old girl a little sparkle!
Gonna have to try and find a local dealer for Amsoil. There was a study done at a lab once about the different axle lubes that was posted on here. If anybody knows where that is, I'd like to see it again. Thanks!

 

I run Lubrication Engineers Monolec 703, 80w90, up front and in the rear.
After I installed my rear diff cover it took about 8 qt also, your gonna love it.

Tim

 

I used the Amsoil Severe Gear 75w140 in both the front and rear diffs. Hot road temps here in NM, plus I tow heavy loads. I installed the MagHytec covers, front and rear, you will need 12 quarts to fill both.

DC came out with a service memo to the dealerships, last summer I think, anyway they are no longer recommending 75w90 in the AAM axles, they upped it to 75w140.

I contacted AAM when I was planning my fluid change, they told me to use the 75w140.

CD

 

Yeah. the 75/140 is the way to go here in Texas. I put a temperature tape on the cover awhile back. To date, the differential oil has been between 200 and 210 degrees. Most i've pulled is about 5,000 lbs. at interstate speeds. That kinda concerns me since we have had a REALLY mild summer due to all the rain keeping temperature down. We are usually already into the 100's by now.... Still haven't had any luck buying Amsoil locally. Time to do some more callin' round.

 

Schaeffers 75-140 for me. Good stuff. It is 115 degrees today.

http://www.schaefferoil.com/gear_oils/167_gear_oil.html

 

I'm running Royal Purple 75w-140.

MikeyB

 

I use non-synthetic Harvest King 85w140 comes in 5 gallon pales for $35 or 2 gallon jugs for about $15.

Works great.....

You can get it at Rural King, or Tractor Supply stores (or equivalent).

I am never paying $5 a quart again for gear oil......

 

Finding a local Amsoil dealer is not something you need to do, as most amsoil dealers will just order it from amsoil for you anyhow. You have a PM about the Gear oil.
Scott

 

Ok, im not a total newby here........but I have a question. How can you tell if your gear oil is really working well?

Has anybody ever heard of our AAM Axles failing due to lack of lubrication?

I have been changing out my Mobil 1 75w90 gear oil every 20k. It looks like new. I don't mind changing it at all. But im just curious what difference (if any) I would notice if I switched to the 140 weight?

Maybe I need to buy that non-syn stuff PourinD uses. His AAM is holding together under obviously stressful pulling conditions.