Anyone else have this problem. I can't believe how rusty my rear end is with 17000 miles? It's not flaking off rusty but it's not black anymore, is this bad ? I was thinking of painting it , but not sure if it's worth it????

 

Cast iron does that. Normal and not a problem. It is thick metal and it won't rust through.

 

Yep...I agree....you're fine

 

You could try to paint with a rust converter or por 15, it should hold up well after that.

 

I think I'm going to do mine with Rust Bullet. We'll see how it turns out.

 

I spray everything under my truck with Fluid Film....no more rust problems at all

 

that stuff is a awesome rust stopper! and it works wonders on already rusted bolts and nuts

 

The under-side parts get very little paint and the areas where salt is used on the road in the winter make it that much worse.

 

that's very normal...and actually good for the metal

the rust is a protective oxide layer. it effectively stops any further rust from happening. once it forms, it prevents oxygen from reaching the metal and forming new rust.

it's the only time you'll ever hear me say "rust is good"

 

Iron and steel will keep rusting until there is nothing left. Maybe aluminum acts the way you think, but not iron.

 

Google it

The protective oxide layer prevents further introduction of the oxidizer...aka oxygen. Now it doesn't hurt that axles/frames are thick metal and have lots of room for degradation

Now disturb that layer and you'll get further rust. We use protective oxide layers in Nuclear Reactors all the time.

 

I think you're confusing the idea of an "oxide rust inhibitor" with "iron oxide". A rust inhibitor might be an oxide compound that protects the metal by slowing the corrosion process. However, iron oxide is just plain old red rust and the iron will continue to rust until completely disintegrated. Surface rust provides absolutely no protection to iron under the surface. I'm not totally certain, but I think the axle housing is made of ductile cast iron.

Not all metals behave this way and sometimes the surface corrosion does put a protective barrier on the underlying metal.

 

you are thinking of "Weathering steel" and for that type of steel, everything you are saying is 100% correct.
Weathering steel - Wikipedia, the free encyclopedia

normal cast or ductile iron and steel does not exhibit these properties. that is to say that all the iron will eventually be converted to iron oxide.

i assume the process you refer to is something akin to this:
http://www.cambridgenanotech.com/the...ckerthesis.pdf

and unfortunatly, does not pertain to this discussion.

to the OP:
don't consume your days worring about it. yes it will rust, and in theory it could rust away to nothing.... but it wont.

here's what it will look like in 30 years if you do nothing:


i can see why someone might think that they are self-sealing, because they generally tend to rust to a certain point and then appear to stop. the reality is that they will continue to rust, but the metal is so thick and the decay so slow, that it is not worth worrying about. notice the frame in the picture. it is in far worse shape than the axle, and yet even the frame is not really compromised strength-wise. the absolute worste case is you'd have to replace the spring perches. but the diff-cover will rot out and need replaced long before that. and even then, that is usually only if they get water in them where it pools at the bottom of the diff.

paint it if it bothers you, but do it because you think it looks bad, not because you are worried about the rust damaging it.

and to those of you who are true truck guys ... i appologize for the clear infraction of brand ediqute.... i will replace it with a more appropriate picture at my earliest opportunity.

if you have no idea what i'm talking about, then you either bleed blue for real, or arent a true truck guy in which case, just enjoy the pic