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.

 

[Chris Ziemer]

Thanks, Blue85, some good ideas. The transmission shop said swapping cases on a 700 in particular is basically rebuilding it. On 350 it’s different, something about the 700. Currently the one have is rebuilt and was done about 10 years ago. Maybe 50,000 miles on it.
For that reason, I’m not even sure if it’s quality enough to swap in the first place. Runs great, yes, but who knows. It could start slipping in a week.

So, fixing it… Just like you said. Weld the plug-in place, I would never need that plug. V groove the cracked area, clean it… I don’t know that you’ll ever get the transmission fluid out from the crack without completely blasting it with degreaser, which of course could get into the transmission.

The plan right now, is to take the transmission out and inspect it. Though, with mirrors and inspecting it myself, I think I know we’re gonna find.

See what our options are. Basically 3K to have another transmission installed. She’s been such a bad girl lately..

 

[Blue85]

I'm curious to hear experience with aluminum brazing rods. Some say it works better than TIG on (previously) oily parts.

If you could find an aluminum plug, it could get brazed over as well. Should a shop ever need access to that port - well, you're screwed, but having access to a port on a transmission you can't drive doesn't really do any good either.

 

[Chris Ziemer]

What an interesting video. Kind of what I’m coming up against is; I’m going to have to pay someone to drop the transmission and do the welding and or braising reinstall the transmission and then see if it leaks. If it doesn’t, money well spent! If it does, then I’m probably going to go to the rebuilt transmission route in which case I’ll essentially be double paying for labor.
Regardless, I think it is worth taking out, seeing if a guy can fix it.
Or option 105 is find a good used transmission and just put that in there. What a shit sandwich I’m eating.

 

[Wes Harden]

If your case is not a K case I wouldn't attempt to fix, just get a new K case and/ or rebuilt.

K case are the 4wd cases. Much stronger through the bell housing, and possibly the tail.

 

[Chris Ziemer]

Thanks Wes, I’ll double check, but I think it is a K case. Are you able to kind of visualize exactly where that crack is at?

 

[Wes Harden]

yes I saw your photo and the arrow. Not sure a K case is any better in that area than a 2wd case. Really does suck. As Blue said if the crack isn't that long maybe adding threads and blocking deeper in the port is a less expensive solution.

bit of drive, The Toy Shop in Pomona did my 700 working great 6+ years later. One man shop, Kendal, only does GM transmission.