http://www.dieselplace.com/forum/smileys/Big Smile.gif Like that Topic? http://www.dieselplace.com/forum/smileys/Big Smile.gif


Anyway, Today I changed out my rearend oil with the Mobil 1 Synthetic. I was amazed to discover that the drain plug was barely tight and had slight weepage but the fill plug was literally, barely finger tight! So take a minute and check your plugs.


Other than that, there was a surprising (at least to me) amount of accumulated gunk on the drain plug magnet.


I also changed my tranny fluid, or at least did a pan drain and filter change. I replaced with 7qts. of Mobil 1 synthetic that specifically said it was approved by Allison.


I didnt know, but there is a magnet that goes on the top of the spin on filter! Be careful not to toss it with the old filter as I nearly did. It was stuck on the filter and I nearly missed it. ~Cleaned it off and put it back over the threaded stud for the filter and I actually heard it click onto the filter just as it was screwed on tight.


~So, I swear my truck is shifting a bit smoother, but I guess it could be hopeful perception http://www.dieselplace.com/forum/smileys/Geek.gif

Questions: What was your mileage when you changed the rear axle oil? What was the condition of the oil when you removed it? Was it really dirty (gray color)?


I've got about 2100 miles on my '04. A couple of months ago when I added over 1.5 quarts to fill the rear axle, I noticed that the oil had a gray color to it. This is a little more discoloration than I have seen in other axles with the original oil.

-Edited by: NCMax

Dura_Mike, I changed mine at 15K and that was too long to leave the breakin stuff in. You need to get the original "gunk" out. I saw a mix of yellowish gold and gray from the front. I was also low on fluid from the factory in the front and rear. (I found the sites late and did the change as soon as I read about it.) I think I read that it is recommended to change after the first 500 or 1000 miles of breakin or something like that now. Don't know how much you use 4 wheel, but you are supposed to change it after the first 500 of use as well.

Im just under 5000 miles on the truck and yes, the rear end oil was pretty nasty IMO. As I mentioned, there was alot of gunk on the drain bolt. It seemed to be very light weight oil and did look grey. I was pretty surprised and I thank this forum alot for bringing it to my atttention.http://www.dieselplace.com/forum/smileys/Big Smile.gif


Now I just need to figure out how to change the front Diff. and transfer case.....

Im just under 5000 miles on the truck and yes, the rear end oil was pretty nasty IMO. As I mentioned, there was alot of gunk on the drain bolt. It seemed to be very light weight oil and did look grey. I was pretty surprised and I thank this forum alot for bringing it to my atttention.http://www.dieselplace.com/forum/smileys/Big Smile.gif


Now I just need to figure out how to change the front Diff. and transfer case.....



Thanks for the info. There are a lot of suspended microscopic metallic particles in the oil of most new differentials. While GM and many others say this is normal due to break-in, the particles do have the potential to increase wear while they are in there with the oil. My oil will come out next week and both axles will be refilled with Mobil 1.

The front diff is easy. http://www.dieselplace.com/forum/smileys/Approve.gif The drain plug is at the bottom and I believe it points outward towards the left front wheel. If you are going to use synthetic in the front diff, you need to make sure you have the "white" breather cap. I believe all '04's already have them.

The Allison is a different story since it has a filter to trap break-in residue, so I’ll wait a little longer before changing the trans fluid. http://www.dieselplace.com/forum/smileys/Geek.gif