Rust on the inside of main caps in rear end

[Ethan341]

Kind of new to doing rear ends and am unsure what to do about this. Upon disassembly of a GM 12 bolt I have found some rust on the inside of the main caps. My question is should I just lightly sand the rust off or is the rear end junk now?

[Mike C]

I'd lightly sand it. Very lighlty. You need to make sure it doesn't lose surface area contact to the bearing race. I'd also get a piece of glass and sand the mating surface of the caps as well to slightly tighten it up.

Place glass on table, place sand paper on glass, pass mating surface of cap across. Maybe 4-6 passes on 120 grit paper.

[bill3rail]

Originally Posted by Mike C

I'd lightly sand it. Very lighlty. You need to make sure it doesn't lose surface area contact to the bearing race. I'd also get a piece of glass and sand the mating surface of the caps as well to slightly tighten it up.

Place glass on table, place sand paper on glass, pass mating surface of cap across. Maybe 4-6 passes on 120 grit paper.

If you use sand paper, I would use much finer grit than 120. I would go with 600 grit or finer.

Bill

[Ethan341]

Thank you for clearing that up I didn't really know what to do there. I sanded them with 400 grit and they have a nice shine now. Hopefully it works and nothing breaks.

[Mike C]

Originally Posted by bill3rail

If you use sand paper, I would use much finer grit than 120. I would go with 600 grit or finer.

Bill

The original machining marks are not that fine and I think the coarseness is designed to help hold the race from spinning.

I’m not a full time diff guy, but I have built well over 30 including installing steel caps on OEM housings. So my comments are based on some experience. But as usual, YMMV.

[ncpetersc]

Originally Posted by Mike C

Place glass on table, place sand paper on glass, pass mating surface of cap across. Maybe 4-6 passes on 120 grit paper.

Not trying to hijack, but what does this do? I have never heard of using glass, is it just to provide a nice flat surface?

[Grumpy old man]

Originally Posted by ncpetersc

Not trying to hijack, but what does this do? I have never heard of using glass, is it just to provide a nice flat surface?

Yes, it's also what you use to flat surface thermostat housings that leak ,A flat sheet of sandpaper laid on the glass gives a smooth even surface . On the bearing caps to remove surface rust using a scotch brite pad is fine ,Your not going to remove enough metal to affect anything It's the cap Not the bearing race, Having rust in the bearing cap just shows at some point there has been moisture inside the housing and changing out the axle bearings/race at the same time would be a good idea .

[VWNate1]

I'd not use any sand paper, a scotcbrite pad or better yet steel wool will o the job and have zero chance of damaging anything .


There are many rust removing solutions available, I use phosphoric acid diluted in water 3>1 with steel wool or scotchbrite pads to easily return to shiny metal.

[ZEKE68]

Something I just learned on this rebuild is that vinegar does a good job of removing rust if you can soak it overnight at least. Then you can wire brush it off.

[VWNate1]

Yes but ;

Vinegar will flash rust as you rinse it off .