Without really knowing specifically what alloy a TH400 is, I would say go with 4043 (consisting of about 5% silicon), because cast aluminum usually has silicon in it so that would be the best match. 4047 (with about 12% silicon) I've heard good things about using for welding dirty cast, but it is much harder to locate than 4043. 4047 is sometimes sold as a brazing rod I've noticed. It has a lower melting temp but is also a "fast freeze" rod (a eutectic mixture of silicon in aluminum.) Only a 10 deg F difference between liquidus and solidus temp.

To prep, make sure to clean the grease and oils out as best you can and scrub all the oxides off the surface in the area you are welding. A "bake" of the area to be welded with a torch until oils in the metal are smoking would also be good. Vee out the cracked areas and fill the gap to ensure penetration. I would go with about a 45 degree or so bevel so and get your tungsten down in there deep, to get a puddle started deep into the bottom of the vee. Expect a little distortion (contraction of the weld bead) from the weld. If you get any stubborn dirty nasty spots, let the work cool, grind out all the dirt and materials surrounding any inclusions to root them out (carbide burr on a die grinder works great for this), then redeposit fresh filler rod in place. If you can access both sides of a crack, weld both sides.

If memory serves you have a TA185, correct? I'd go heavy on the EN balance % and hit it with all 185 amps you've got to minimize the heat input into the rest of the transmission. Assuming the bellhousing is relatively thick stuff. Some pre-heating with an air-propane torch may be helpful if the area to be welded is particularly thick.

 

Brake-Kleen works good to get the oils out of the crack(s) as well. Spray - blow dry, spray - blow dry, repeat as needed until there's no more oil/grim rising to the surface. Grind out and repeat.

It also helps identify the end of the crack(s) as does the heat that jakeru mentioned but don't heat the Brake-Kleen for the reasons stated in past threads regarding the dangerous fumes from burning liquid forms of brake cleaner products.

 

brake cleaner on porous castings



1-Duane, you're presuming that the air blow off will positively remove all
the brake cleaner, including that which is mixed with the crud and grime--remaining after blow off and whatever may find it's way into casting pores and on the opposite side of the break.

This is somewhat dicey to do--hopefully if one's doing the brake clean route
(which has been repeatedly flagged with stickies--as a potentially disabling
to fatal method).....then 'hopefully' they'll recognize that particular smelll of
liberated chlorine compounds--which can eat their lungs, before it eats their lungs.
Fooling around with brake cleaner as above is a dangerous thing to do.
Yes--you do it and get away with it---I won't.

**I have relatively little experience actually welding aluminum bell housings,
only having done over 241 in the last 23 years--below is what works for me:

2-TH is turbo 400 trans. The older trans. have less casting porosity than the newer ones---which can exhibit amazing porosity--more than 50%.

-4043 works good.
-I use lacquer thinner, water cleaners
-Groove prep breaks with carbide burrs, some grinding
-on inverter machines--running full unbalanced--like 10% EN,
with sharp point on ceriated, thoriated, lanthium tungsten--produces
a tight, focused arc with max. heat input.

-running min. AC freq. CPS adds to max heat input

-Many of the 'experts' on this site-don't understand/have never used
focused AC--on decent inverters.

-focused max. heat will do much more, easily, quicker than screwing around
with cleaning action on AC. To repeat-focused heat works where all other methods-fail.

-in contaminated and porous castings--it can become an exaggerated form of 'bump-welding', jamming the rod in under the crust. Tack up, weld one side, then back groove and weld the other side.

--bell housings by their shape are a restrained casting, which can further crack
or distort from the heat of welding. Using intermittent water spray cooling with air blow off helps.

--after repair, the bell housing flange faces need to be in same plane--via temporary bracing/clamping/inspecting with straight edge. Some prior inspection and repair planning helps.

-most breaks on the flanges are caused by incompetent assembly attempts,
not having the trans./input shaft lined up properly, then attempting to 'draw the
trans. up tight to the block, by tightening a nut/bolt. The perpetrator needs to understand that this is what breaks things, big time.

 

My neighbor gets these from dealers and shops all over, and in my thinking does them a bit wierd.

He doesn't spend much time cleaning, maybe some wiping of oil and grinding the crack. When he welds it's very hot and often he'll shove a ton of rod in the puddle sagging it to the other side (I mean a real blob here).

After finishing one side he cleans (cuts/grinds off) any mess from melt through and lightly grinds the other side and welds a reinforcing bead on the backside.

It's hard to argue about how he does it as it goes pretty quick and folks keep bringing more housings when they bust them. He does much the same when pieces are broken off, so I'm thinking he just sees the junk comming up and sags it through to get rid of it.

Must be that practice, practice, practice thing... it just looks wierd.

Matt

 

He has gotten used to the porosity and it's shortcomings. I have done some engine case covers and a bell housing, they were a big headache when trying to be nice with them. What I found that worked best for my welder was to grind the crack, and drill the ends to stop the crack. Clean them with acetone and a scrub brush. Set the machine with a low frequency. I found the high frequency with cast material leads to a lot of cracks around the weld, and a LOT of cracked welds with 4043 filler. On the other hand, adding a lot of filler with the frequency about 65-70 was OK, and it did not crack the housing any more. I still like the 5356 filler more than the 4043. I saw too many cracks in the 4043 for my liking. It was primarily from weld shrinkage, it was easy to see how the cracks formed.
But yeah, grind off the sag on the inside, and put a decent bead in there. You will see a LOT of opening up as you get the puddle going. Amazing how much lost open space there is in cast aluminum!

 

Would really have to see the bell housing and where and how it is cracked.

May need to bolt it up to a steel engine block to keep it from warping and then recheck after welding.
It should be tacked and welded on the inside FIRST then welded on the OUTSIDE LAST.

Many considerations.
I would preheat a weldment that large and that thick before TIG welding..

If it is for racing I would not weld it at all.

Aluminum is in the as welded state is 64 % strength of the parent metal.
For street use it is ok.

 

4043 is what i use to tig alu cast stay away from brake clean just not worth the risk
-clean clean clean and clean again stainless brush and acetone works best for me
-Use carbide not a grinding disc as the disc will just contaminate your weld again
( i use a skill saw to groove with a die grinder works just as good but takes longer)
-use a something as a jig to hold everything in place
-weld it up on one side then groove other side weld it then cut out the weld and do it again
-and if you want a nice finish wash the casting bubbles out with the tig
cheers and hope this helps

 

Duane:drinkup:

I use brake cleaner frequently. Lot's of it. I don't have any problems welding with the non-chlorinated stuff. Still burns my eyes a bit after the heater burns the fumes, but as far as welding goes......no problems. Spray paint fumes run through the heater burn too. I just open the overhead door frequently to swap out the air.

 

5356 is your best bet in this situation..

...zap!

 

Yo Zap did you get my PM about not being able to send PMs?

 

hmm, I have an idea of eventually replacing my tranny with a awd stick tranny & this will require me having to cut a bell housing in half & then weld that to the replacement tranny. the replacement tranny does not use a separate bell housing at all, it's all cast into the main tranny case but I want to cut the front off & then weld the front on from a different bell housing. I'm going to be making somewhere in the neighborhood of 600hp, does this sound like it's doable?

 

I would do it and just try to weld some webbing and gussets on the housing. Making the joint jagged instead of straight will also help by giving it more surface area and a non linear joint will be less prone to shearing

 

yup hell of alot less scarey then brake kleen

 

My point is all chemicals require proper use and precautions. Never said or meant to imply it was worse than brake cleaners.

 

I have found that once they crack they typically will crack again so I am using this now. They have them so you can but GM behind a mopar or Ford as well.
NEW JW Ultra Bell Bellhousing Turbo 400 to GM

http://www.plunderhere.com/auction_details.php?auction_id=2310998

 

I have welded TH-400 tranny's before and the weld will depend on how clean the casting is....4043 is typically what you use on most cast aluminum any dirt in the casting will show up as a porosity in the weld and not be as strong as possible if it
was clean......Does that make sense? Anyway welding should be your LAST option
in my opinion....