33 BB driveshaft?

[Mart]

I'd like to see a photo of the crack before offering any advice on whether welding it is a good idea.

Is this a shaft or a torque tube?

If welding a shaft, it will bow towards the weld when cooling. You can mitigate this by putting a roughly equal amount of weld on the opposite side to equal it up.

But not knowing where the crack is, it is impossible to offer good advice.

Mart.