I can't believe the rust that is developing under the truck. My 73 Chevy isn't as rusty. I thought the newer trucks would have more corrosion resistance. I was thinking of getting out the oil can and lubing everything up.

 

my 05 looks like its brand new, however the 04 sounds like yours

 

my 04.5 looks brand new underneath and i live in the rust belt. but i do have my truck sprayed yearly at carwell

http://www.carwell.com/

 

Most of the underside looks good on mine, but the diff cover looks like it's from a 20 year old truck, covered in orange rust. I think they used black magic markers on it instead of paint..

 

I have the same problem on mine. I think that when i change the diff fluid that i will sand the rust off pretty good and try to repaint it. It is the only thing on my truck that is rusty and it kind of sticks out so i might as well try it.

 

My truck diff rusted, paint was chiping off. Then dealer tells me that it's my fluid getting hot, . Truck only had 10,000 miles at the time. I got a metal brush and busted all the rust and paint falling off, then repainted with rust o leum flat black, haven't had a problem again with it rusting or paint flaking. My hard earned 40 G's at work for a brand new truck Could you believe that.

 

becarfull to look at your brake fuild. there is a brake line T on top of your diff. if all is good, sand and repaint with stove paint. diffs can get hot. although i agree about the 40 Gs.

 

DTR Member "Bluebull" mentioned in another thread that the AAM axles get extremely hot at first while they are breaking in. (Like 600 degrees). After they break in they cool down alot and never get close to being that hot again.

I suspect that that is what hurts the paint on them while new. I remember my diff cover was starting to rust a little bit too, but I replaced it at 15k with a Mag Hytec cover when I changed out the fluid. The orginal fluid looked horrible too and had a gray paint tint to it. Bluebull said AAM uses some sort of gray marking additive or something in it. Anyway, I was glad to get that nasty stuff out of there at 15k. Since then I have run Mobil 1 75w90 and changed it again at 30k and 50k. It looked like brand new fluid coming out.

I know it sux that the paint is rusting or flaking on the stock covers, but apparently the extreme heat on break in is normal. After that, if you repainted the cover it should be fine.