Just cleaned up a 4speed z transmission and noticed a crack in the casing (see attachment).

I tried to turn the bolt to inspect further and it let go. Is this a common failure point?

Edited May 20, 201113 yr by Blue
removed '71 240z

Can't say anything about what it came out of most recently, but that is a Type B transmission. Introduced in US 240Zs in '72. All US '70-71 had the Type A (aka Monkey-motion) box.

Can't recall that I've ever seen a Type B break there, but 98% of my tranny experience is with the early boxes.

Edited May 21, 201113 yr by Arne
typo

Thanks! That actually helped a lot! I have 3 transmissions and I got the 71 4speed (monkey box) mixed up with that one.

I've never seen that failure, though I did have to swap my 260 trans after the case cracked where the rear seal seats. I had a dif break in a race and the vibrations must have cracked the case. The internals are fine, so I'll use it for parts if needed.

For what it's worth that looks pretty fixable, a good TIG welder could take care of it pretty easily (and cheap). I've welded a few transmission housings for different cars, it's nasty aluminum to weld, but with careful preheat it's very possible.

I think someone or something (the Force?) is telling you to get a 5 speed.

Just cleaned up a 4speed z transmission and noticed a crack in the casing (see attachment).

I tried to turn the bolt to inspect further and it let go. Is this a common failure point?

Yeah, I think that are common failure point. I hope that you can fix it.

That type of break is easily fixed with with a torch and the HTS 2000 welding rod. http://www.aluminumrepair.com. They are kinda pricy, but priceless for fixes like this. I have used them and love them! Think custom manifold creation...., repair that broken bolt hole in the corner on the front cover or head, that kind of thing is now childs play with HTS 2000 rods...