welding auto trans cases?

[fordtek1]

I have ran into several cracked trans cases here lately and was wondering how is the best way to properly weld a cracked case? I have the following equipment available- 250amp snap on mig welder w/ alum spool gun, oxy- acetylene torches, and a + polarity tig welder. What are my options and what are the best methods to fix these annoying cracks?

[pauljr]

i wonder if you could get clean enough (fluid residue) once v-ed out to weld

[84ZMike]

If it is a place that fluid has traveled.....ie ports etc of the case D.F.W.I. (don't f### with it)........I say this not because of the contamination (also an issue),but the tight tolerances of the tranny itself............. if it is like the bell housing etc then looks like your best bet would be to MIG it with that spool gun.........also depends on how/why the case cracked......as your weld will not be as strong as the original casting..........also with the way things are going with tranny and eng remans. it is simply easy , quicker,and more cost effective to just get a reman. and install it.....better warranty and the car/truck will be in the shop less time.....

[fordtek1]

thanks, the cracks are in non-structural areas and have usually resulted from broken mounts, etc....

[Mark71GTX]

I actually welded the bellhousing on a co-workers F350 (powerstroke - approx 1995 with the smaller diesel) It had a piece of it near the pivot broken off completely. I welded it with an aluminum stick rod over four years ago and it is still holding today.

[fordtek1]

I tried welding it with a mig spool gun and as soon as the weld cooled, it cracked right next to the weld bead. I took it to a pro welder who tigged it and the same thing occured. why did it do this?

[Steve]

Could be the tranny case is not Al but Magnesium. Clean off a spot and put a drop of Welco liquid flux on it. If its Al there will be no reaction. If its Mg the spot will turn black right away. In which case you need Mag filler rod not Al filler.

[Mark71GTX]

It may be an off the wall alloy or a poor grade - or like Steve said, it might be another metal altogether. I didn't have that trouble with the bellhousing I repaired, but maybe you can treat it like cast iron - preheat the weld area and keep heat on it after it is welded - slowly cooling it down afterwards. I know cast iron will spider web on you in a second, maybe it is similar. Just a theory.

[Toysrme]

First determine exactly what metal composition the case is. (As best as possible). Clean it with simple green, or whatever you like.
The last thing you do two minutes before you go to welding it. Use acetone to REALLY clean that grease up. Start welding as soon as it evaporates.

Acetone is nasty, but unlike most cleaners, it will simply dissolve oils & evaporate quickly.

[JonnyTIG]

There are oxy - fuel fillers available for Aluminum repair which claim to be as good as tig, however ac tig is your best bet in my opinion. The proper way to do the repair would be to use an oven to preheat and maintain the case at a suitable temp while welding. Regaurdless of the type of material, holding the dimensional tolerances is important when working on trannys or engine blocks. Welding any kind of casting results in stresses and pulling, and an oven will bring the casting up to temp, hold it, and reduce the temp in uniform, reducing if not eliminating the stresses. Without ac tig, your best bet is oxy - fuel, however it my be difficult to stop warping, depending on the joint configuration. Stick will work good if you can control distortion, and if you can run it well. I've been welding aluminum for several years but can't offer anything in the way of SMAW Al advice. I have repaired tranny case cracks resulting from 'one bolt being left in the hole while prying it apart', and a simpe plate holding fixture helps when conditions aren't at the best.

Here is a couple pics of an 'open to closed' chamber conversion I did on a cylinder head using an oven. The results measured out to less than 0.004" distortion on the head gasket surface, and the welds cleaned up well.

Al mig can work however knowing what base metal alloy you are working with and matching a filler can be tricky.