Buddy of mine told me I was supposed to chang ethe rear end fluid after 500 miles in my G80? He said his 02 2500 HD told him to do that in his owners manual, anyone else heard of this? Don't want to overlook anything I should be doing, but I can't find it in my owners manual. Thanks guys!

I can't say by specs. when you're technically "supposed" to do it but it seems from everything I've read on here that most everyone changes out the front and rear diff. fluids by around 1000 mi. or as soon as they can find the time to do it...I just changed mine out at around 2150 mi. on my LMM...and oh man...the fluid was nasty looking...hope that helps you a bit

Hang on, was I supposed to change mine out?? I have almost 30000 miles on my truck and have not changed it. I was going to do it around 40000 or 50000. What brand do you use??

Normal practice to change the rear diff. fluid after the first 500-1,000 miles. A lot of break-in wear takes place & you will want to get that fluid out of there. It's also a good idea to check the fluid level within the first 500 miles, some are quite a bit low from the factory.;)

I have read a lot of threads on here saying that GM fills the rear differential low from the factors. I already had my LMM for 3,000 miles when i read that so i promptly went outside and checked; sure enough it was low. When i did my change some pretty nasty stuff came out. It was very black, looked like someone has sprinkled glitter in it and had a lot of air bubbles in it. I am not sure what the intervals are but i am certain that it is less than 30k. I know that there is a sticky in the maintenance section. I changed out my front and rear diff as well as my engine to amsoil synthetic. I used what is listed in my sig. I purchased it from Heath who is a supporting vendor. Shipping from him was only $30 bucks but i didn't mind paying because he was VERY informative.

There is no "requirement" to change differential fluids in the first 1000 miles or so.

However, I do subscribe to the concept, as I believe it's a good idea. It helps flush out the initial "break in" materials including wear metals, any casting sand remnants, etc. Further, lot's of these rear diff's tend to be shipped from the factory on the low side for quantity of fluid, so it's a good idea to check it at the very least.

Plenty of good fluids to chose from. Here's the lastest study showing the good and not so good of several:
http://www.amsoil.com/lit/g2457.pdf

I did it based on the fact that a lot of guys on here did and that it was in fact low from the factory. When I did I was glad. The oil looked and smelled horrible and had a lot of machining filings in it.

The rear-end manufacture (Not GM) recommends that the lube be replaced after 500miles with no towing. The theory I subscribe to, is to add another 500 miles towing to that then change the fluid out. Now I change it out every 50k.

Thanks guys! I will change it out the first of the week. I only run Amsoil in all the fluids of the truck, so that's what will be going back into it. Even if the manufacture doesn't say you need to, it makes total sense what you guys are saying, a little bit of prevention goes a long way! Thanks again, this site is GREAT!

The way I figure is that you definitely don't want anything going wrong in the differentials so a changeout once and then every 50K after that isn't a bad deal at all...