Axle housing...structural or isurface casting flaw?

[Wkndwarrior]

Kind of new to the group and this is my first post. I bought 4.56 gears to install on my KK. Plan is to do the front first and then the rear afterwards. Since this my first time working with gears, I pulled a junk yard front axle housing to perform the gear change on and have time to complete it without "parking" my daily driver for an extended period of time. Then do a weekend swap. Upon cleanup and inspection of the housing I noticed numerous cracks. They don't look structural but wanted to know if anyone has seen this before and is it more of a casting issue? Additionally, what would be a safe tolerance of grinding and/or sanding. I have searched for literature on this and have not come up with much. Thanks for any help you guys can offer.

2009 KK
JBA 3.5" Tommudd's Lift
32" Falken Wildpeaks

 

[lfhoward]

I have thought about doing the exact swap you are, with a junkyard front diff too! I will be following along and paying close attention.

I also will love to know what your experience will be with 4.56 and 32’s. I have 31’s and will need 4.10’s but I am considering 4.56 for towing.

To your question, looks like it’s the original casting to me that was not a perfect surface. Those don’t look like cracks that formed after the fact. But I have not been inside my front diff yet so you may want another opinion.

 

[KJowner]

Hard to say from the pictures, do the suspected cracks show up on any of the machined surfaces or only on the 'as cast' bits? It could well be casting marks from the aluminium hitting the cold die surface during casting.

 

[MsRandiCook]

That doesn't look good! Could be from a cold injection when die casted. Use some non chlorinated brake cleaner (lightly) and clean. Watch for a oil weep from the area. If you see oil after a quick clean, it could a crack.

 

[Wkndwarrior]

The cracks are not on the machined surfaces. They look spotless. I have found some literature on the cold injection process, but since I'm no metallurgist or mechanical engineer, I wasn't sure if that is what it was. If so, would it still be usable if no oil weeping occurs after cleaning?

 

[MsRandiCook]

The cracks are not on the machined surfaces. They look spotless. I have found some literature on the cold injection process, but since I'm no metallurgist or mechanical engineer, I wasn't sure if that is what it was. If so, would it still be usable if no oil weeping occurs after cleaning?

If you spray and no oil weeps, I would use it.

Cold injection is when the aluminum or mold is colder than it should be for making parts. That's when you see potential cracks in the parts.

To be sure, go to your local welding supply store and purchase some die-penatrate. Clean the housing, let it dry, spray the die color on first, let it dry. Then spray the white on and if you see any color come looking like a crack, you have a bad casting.

 

[Wkndwarrior]

That is fantastic information. Thanks for the assist. I'll keep the post updated with what I find.

 

[MsRandiCook]

That is fantastic information. Thanks for the assist. I'll keep the post updated with what I find.

I really hope it's good. Looking at the photos again, I'm not sure. A good thing we have access to other axles out there, it's bad.

The die-penatrait is a must at this point. Looking forward to see how it goes

 

[Wkndwarrior]

Completed the inspection on the salvaged housing over the weekend with the die penetrant system and it looks like I'll be buying a new housing. Even the one I currently have installed looks to have the same type of surface cracking. Thank you all for your help.

 

[MsRandiCook]

Completed the inspection on the salvaged housing over the weekend with the die penetrant system and it looks like I'll be buying a new housing. Even the one I currently have installed looks to have the same type of surface cracking. Thank you all for your help.

So glad you checked it out! Keep us posted.

 

[KJowner]

Before you get too carried away buying another that's probably the same, try gently cleaning the cast surfaces with a die grinding and a carbide burr, if it's just casting marks it's probably only a few thousandth deep, remove the flaw and the stress riser is gone. Obviously don't touch machined surfaces....