I've tig'd a couple of trans cases , even filled holes , no problem.

Got it...........Thaxs Gents.

i'm not a tig welder, but anything i have read up on concerning tig welding in general stresses cleanliness no matter the material being welded. stanton suggested to not clean the crack because it was a fresh break. that may be so, but the case surely is dirty [because of the skin porosity], and you would be welding to it. plus the case casting is not really a very high quality of casting is it ? i have a new tig outfit in it's box that someday i hope to learn to use, so i try to read up and learn as much as possible. i have also read you should be very careful when v-ing out a crack or beveling a joint in preparation for welding aluminum you should be careful to not contaminate [make dirty] the joint prep by using a disc, stone or cutter previously used on other material. is this true ? the thinking is the same as grinding your tungstens on a dedicated wheel.

Were planning on welding it up on Wednesday, I have a junk case I'm going to practice on first to find the best settings for the welder.

Plan on v-ing out the inner section of the bellhousing first with a fresh burring bit (the surrounding area already cleaned up with 36 grit ro-lock) , drill and chamfer the crack end, de-greasing the area with a little acetone, hit it with the propane torch to warm up the area and burn off and chem, weld up the inner and then grind out the outer and repeat.

Yes, alum and cleanliness are an illusive goal in welding alum. Everything, as you suggest, that comes in contact with the area, only seems to contaminate the weld. On other threads, I've suggested even dedicated alum tig gloves, to keep the tig rod clean that you handle. I think there is something to welding used/weathered alum castings with non visible porosity concerns, it seldom/never matches the results of when welding new alum, no matter how clean one tries to get the weld area..

edit: Lacquer thinner has always been my favorite alum cleaner, it seems to have a wider range of solvents, since the exact contaminates are not always known, although acetone is promoted as a stronger solvent?

As mentioned, grind it out and clean with acetone (no brake cleaner, it can cause phosgene gas.) If you can get an A/C TIG welder if will do a better job as the AC helps clean as it welds.

Cast aluminum absorbs fluids like a sponge. I've fixed broken mounting ears on Holley base plates in the past. Wash, clean, acid, v the edges, all of it, and when you strike an arc and make it melt, it smells like the exhaust of a running engine - strong enough that you don't want to breathe it. Water pumps and housings - like exhaust from something with a blown head gasket. Perfectly clean motorcycle cases - like oil on a hot exhaust.

One trick is to use a TIG torch, strike an arc and work the area of the crack as if you were going to weld, making it hot enough to melt without adding filler. Contamination will come to the surface and can be cleaned with a wire brush, carbide, etc. May have to do it a number of times, but you should be able to get it cleaned to the point where you can add filler and get it to flow and freeze without looking like puke. If it doesn't look like chrome when it melts, it has junk in it. Propane works to preheat and clean the surface, but it really doesn't cook the contaminates out of the casting. The quality of the casting has a lot to do with it also. Some castings are made from garbage and turn to dog poop as soon as you make it melt. Aluminum can run smooth as silk or it can turn to junk and make you say bad words. It just depends.

A NEW stainless wire brush used every time you stop the arc. V with Carbide. Wire brush, wire brush, wire brush

Your saving grace may be that the bellhousing area is not continuously in contact with hot oil as is the body of the trans. As a result, it may clean up and weld just fine without having to go through all of the dramatics. Just have to strike an arc and see what it does.

I had to weld this up for my brother.. its his
bike engine.. mounts to the oil filter

Then I milled it flat... bored and rethreaded it
for a remote filter

Mike what tig r u using?

Lincoln square wave.. not a bad unit but I like
Miller better... I've had this unit about 20 years
When I was working.. 95% of my tig was with a Hobart
300 water cooled machine.. loved that big thing

As a non-welder can someone expand on the absolutely no brakleen to clean the area.

The reaction to the heat of the welding causes a poisonous gas that is lethal when inhaled.

this product creates phosgene gas. similar to mustard gas. when inhaled, it removes oxygen and you die. there are numerous documented death cases as well as some very close near misses, some of which survived only to have severe brain damage. a very dangerous product to use for cleaning anything you will weld on. the newer labels on the can state to not use the product for this purpose due to just this reason.

My experience was, IMO much more dramatic. I knew the cautions, not sure if they ever presented themselves, welded for 4+ decades, I seldom used brake cleaner for pre weld cleaning. However, I had a 4"? crack in the tongue area of my Alum Featerlite that needed tigging. It was not possible to fully v groove from both sides. The crack was nearly a year old. I wire brushed w/SS, I v grooved, I lacquer thinned, and lastly, I thought a shot of brake cleaner might blow out of the crack of anything I had missed. Hours later, in 85F, in Florida sun, outside, in moving air, I tigged the crack. Hour? later, for 24? hours, I thought my chest was in a vise, breathing was difficult. Never again. There was no discernible odor. I suspect the cleaner reacts/or leaves a dried residue, that the intense welding UV reacts with.

I looked into the cause a while back, but I thought some chemical component (maybe in the clorinated brake cleaner) reacts with the UV light and creates the phosgene gas. Found links to how the gas was used in Word War 1. And I think one source mentioned the gas acts like a corrosive acid on the lung tissues.

Blowing it dry with a blow gun, allowing it to air dry for an extended period, etc doesn't make it safe. Remember, cast aluminum is like a sponge.

On a related note, using brakleen anywhere in a shop where there is an open flame (wood stove, kerosene space heater, etc.) is the same situation. I made that mistake many years ago, once. Bad stuff.

Yup, acetone is the way to go. I wipe all my parts and filler rod down with acetone.

Brakekleen will kill ya.