Corrosion inside rear differential?

[Mikead40]

So a few months ago I changed out my rear diff fluid and cleaned the gears etc with brake cleaner. It looked like this
.

I reseated the stock cover with rtv and filled it with royal purple. Good to go.

Last weekend I noticed a small drop of fluid on the bottom of the diff cover - and on closer inspection the bottom lip of my cover was bent back very slightly.
Other than that it was working fine - no excessive noise, slippage etc. Today I took off the cover (it still had plenty of gear oil in it) cleaned with brake cleaner and it looked like this




My question(s) - I'm assuming that reddish brown stuff is rust, however it seems to rub off easier than I would expect rust to. Is there any possibility it's something other than rust? Has anyone seen this before, and do I need to be concerned about it? I'm waiting on ups to deliver my new diff cover, so it's currently sitting in my garage with the diff cover off. Is there anything I should do before installing the new cover and filling with gear oil? I plan on using The Right Stuff instead of regular rtv this time.

Any advice would be really helpful - thanks.

 

[ridg3runner]

You been thru any deep water? Check your vent hose for holes.

 

[Mikead40]

You been thru any deep water? Check your vent hose for holes.

Thank you for replying
A little water, but not much - super dry here in TX. I will check the breather tube - it's actually relatively new (I lost my old one before - which is what prompted my first rear diff cleaning) and held on with a tube clamp.

 

[ridg3runner]

How did the old fluid look? Was it even slightly milky at all?

 

[Mikead40]

How did the old fluid look? Was it even slightly milky at all?

Negative. Completely black - about the same consistency as the last time I changed it. What would milky mean?

 

[ridg3runner]

Negative. Completely black - about the same consistency as the last time I changed it. What would milky mean?

Evidence of water. Probably just a fluke, wouldn't worry too much about it, just be sure the vent tube isn't damaged, toss it back together and rock on. If you want, you could try a different brand of gear oil but it probably isn't necessary.

 

[Mikead40]

Evidence of water. Probably just a fluke, wouldn't worry too much about it, just be sure the vent tube isn't damaged, toss it back together and rock on. If you want, you could try a different brand of gear oil but it probably isn't necessary.

Cool - sounds good. I appreciate your help :beer:

 

[MC2003TJ]

Cool - sounds good. I appreciate your help :beer:

The problem is that you are using brake cleaner!! When you use brake cleaner it strips away all of the oil that protects the metal from rusting and then moisture attacks the metal instantly. When servicing the differentials you should let the housing drain on it's own and then use a rag with solvent on it to clean the gasket surface only.

You now have rusted parts that will contaminate your new oil.

It is a good practice to spray metal parts after cleaning with WD40 to keep them from oxidizing/rusting.

Hope this helps.

 

[olram30]

The problem is that you are using brake cleaner!! When you use brake cleaner it strips away all of the oil that protects the metal from rusting and then moisture attacks the metal instantly. When servicing the differentials you should let the housing drain on it's own and then use a rag with solvent on it to clean the gasket surface only.

You now have rusted parts that will contaminate your new oil.

It is a good practice to spray metal parts after cleaning with WD40 to keep them from oxidizing/rusting.

Hope this helps.

That's strange. Even Eddie recommends brake cleaner..

 

[Mikead40]

The problem is that you are using brake cleaner!! When you use brake cleaner it strips away all of the oil that protects the metal from rusting and then moisture attacks the metal instantly. When servicing the differentials you should let the housing drain on it's own and then use a rag with solvent on it to clean the gasket surface only.

You now have rusted parts that will contaminate your new oil.

It is a good practice to spray metal parts after cleaning with WD40 to keep them from oxidizing/rusting.

Hope this helps.

Huh. Thank you for your input. That's news to me as well. I've never heard of someone saying not to use brake cleaner. I did first hear it in the differential cover write-up that Eddie did. When you say a "rag with solvent" - what type of solvent are you referring to?
I had not heard the WD-40 thing before either - does anyone else do this?
Thanks again.

 

[MC2003TJ]

Huh. Thank you for your input. That's news to me as well. I've never heard of someone saying not to use brake cleaner. I did first hear it in the differential cover write-up that Eddie did. When you say a "rag with solvent" - what type of solvent are you referring to?
I had not heard the WD-40 thing before either - does anyone else do this?
Thanks again.

Well, I would not use brake cleaner unless I suspected that I had lots of metal debrit that I was trying to wash out of the differential housing. Then I would coat the metal parts with a light film of WD40 to keep them from rusting while I put the differential cover back on and let the sealant set. Then I would fill the differential with gear oil as soon as possible.

I would not spray down the gear case with brake cleaner for a routine service if everything looked good. The first picture you posted looked great and I would have put a new gasket on and filled it back up.

The solvent that I prefer to use is Mineral spirits. Sometimes I use brake cleaner on a rag and wipe the surface to be sealed. I also use a solvent by loctite that is a green cleaner and not so aggressive like brake cleaner.

Perform your own test on a piece of steel or iron and see what happens. When you spray the metal with brake cleaner it will start rusting immediately. Coat that part with WD40 and it will not rust for months. This depends on the humidity in the surrounding air of course.

 

[Mikead40]

Well, I would not use brake cleaner unless I suspected that I had lots of metal debrit that I was trying to wash out of the differential housing. Then I would coat the metal parts with a light film of WD40 to keep them from rusting while I put the differential cover back on and let the sealant set. Then I would fill the differential with gear oil as soon as possible.

I would not spray down the gear case with brake cleaner for a routine service if everything looked good. The first picture you posted looked great and I would have put a new gasket on and filled it back up.

The solvent that I prefer to use is Mineral spirits. Sometimes I use brake cleaner on a rag and wipe the surface to be sealed. I also use a solvent by loctite that is a green cleaner and not so aggressive like brake cleaner.

Perform your own test on a piece of steel or iron and see what happens. When you spray the metal with brake cleaner it will start rusting immediately. Coat that part with WD40 and it will not rust for months. This depends on the humidity in the surrounding air of course.

Well, hopefully I don't come home to more rust because my jeep is sitting in my garage with the diff cover off after having sprayed the inside with brake cleaner. I'm at work overnight, so I guess I'll have to see in the morning.

Since using brake cleaner seems to be fairly common practice for cleaning diffs, has anyone else used it and noticed their diffs starting to rust?

 

[MC2003TJ]

Well, hopefully I don't come home to more rust because my jeep is sitting in my garage with the diff cover off after having sprayed the inside with brake cleaner. I'm at work overnight, so I guess I'll have to see in the morning.

Since using brake cleaner seems to be fairly common practice for cleaning diffs, has anyone else used it and noticed their diffs starting to rust?

Oh no! I have been a mechanic for 23 years now and I will bet you lunch that you have more rust on everything when you get home. Spray it down with WD40 and then wipe it clean. Fill it with oil and then service it again in a few weeks to see how it looks. The rust will pit the bearings if it gets real bad. Best of luck!

I am actually in the process of changing my gears and have had the diffs. Open for a few weeks and no rust at all. It was supposed to be a weekend project until my wife decided to have our baby 5 weeks early. Got to roll with it.

 

[Mikead40]

Oh no! I have been a mechanic for 23 years now and I will bet you lunch that you have more rust on everything when you get home. Spray it down with WD40 and then wipe it clean. Fill it with oil and then service it again in a few weeks to see how it looks. The rust will pit the bearings if it gets real bad. Best of luck!

I am actually in the process of changing my gears and have had the diffs. Open for a few weeks and no rust at all. It was supposed to be a weekend project until my wife decided to have our baby 5 weeks early. Got to roll with it.

Thanks again for the advice. Congrats on the baby!

 

[tastethebeast]

I have always used brake cleaner and wiped it down really good. It looks like some water got into your differential and was there for awhile. Just be careful after you go through deep water and check your cover bolts for tightness every so often.

 

[JayKay]

That's strange. Even Eddie recommends brake cleaner..

I agree with everything MC2003TJ has mentioned here. When Eddie recommends using brake clean, I'm sure he's not spraying them down and leaving it sit for an extended period. Most likely the parts are getting sprayed with brake clean and filled/covered with oil right away.

 

[JayKay]

Even when I worked in an automotive restoration shop, sometimes we'd have a car stripped to bare metal while doing fab work or sheet metal straightening. We'd spray all of the bare metal that was not being worked with WD40 to prevent surface rust/contamination. If we didn't, we'd leave the shop at night and come back the next morning to a brown car.

 

[cozdude]

Water had to get into his diff and sit for a while because I clean my with brake cleaner all the time and it doesn't look like that. I have the smallest section of surface rust/corrosion in my rear diff but that's because I had a leak on the bottom of my diff and water got in.

 

[JayKay]

Water had to get into his diff and sit for a while because I clean my with brake cleaner all the time and it doesn't look like that. I have the smallest section of surface rust/corrosion in my rear diff but that's because I had a leak on the bottom of my diff and water got in.
View attachment 99656

But do you put yours right back together and add oil or leave it sit a while after spraying it down before you put it back together?

 

[cozdude]

But do you put yours right back together and add oil or leave it sit a while after spraying it down before you put it back together?

i let it sit when i pull the cover off. there thends to be some residual oil left over that i let drip out and then i spray it down with the brake cleaner, let it sit, then paper towel out the extra oil, cover up and refill. takes me about and hour to do one diff because of me sitting and letting it drip and dry a bit.