Cracked transmission housing.

[Chris Ziemer]

Well, I really got myself into a predicament here! I have a perfectly fine 700r4 transmission in my Blazer, however, at some point, somebody tightened one of the inspection port plugs, too tight creating a hairline crack in the housing. The crack is on the opposite side of the arrow, along that tube. Not sure how far it extends out. Probably not very far.

It’s been leaking for a long time, though the leak is always been elusive because it only leaks went under pressure. I.e. reaches temperature. As a late, it’s just leaking like a sieve all the time.
Question is, can it be fixed? I tried to clean it and JB weld but it didn’t work at all. I’ve heard people can drop the transmission and weld it, but it’s not always successful.
Otherwise, I’m looking for a good used 700r4.

The picture where the location is, faint arrow pointing at it. Those holes are tapered so when tighten too tight, it cracks the aluminum.

 

[Blue85]

A good welder can probably drill, clean and weld that, and the pipe thread could likely be re-tapped, but I'm not sure if it can be pre-heated well unless the case is emptied. With an empty case, things get a lot simpler, but that's also a perfect opportunity to swap to another known good case. I've also heard of aluminum brazing rods. Again, you'd have to grind the crack and clean really well.

I wonder if you really need that port. I believe it's the 2nd gear pressure port (it may only leak when you're in 2nd gear and above). It might be possible to shove a plug in there such that it can be cleaned really well without getting stuff into the interior. This is a crazy idea, but if you're at the place where the case it pretty much a loss, it might work. With the pan off, and whatever has to be removed to get to that "pipe", clean the pipe as best you can (including wire brush), tape it closed from the inside, fill it up with JB Weld and put the plug back in. It might also be possible to find a piece of tubing with the same OD as that "pipe" ID and glue that in place, using some alternate plumbing fitting to cap it off. This seems kind of risky to me since pressures inside can reach a few hundred PSI. For the risk of pulling and tearing down the transmission again, it might not be good odds.