Italian Carro Armato P40 tank secondary armament

I'd say there are more negatives to swapping out an MG34 for the Breda.  1) we assume that the co-axial Breda stayed the same.  2) You'd need to switch out different ammo racks for the MG34's ammo packs vs. the Breda's ammo magazines.

Plus, where would you stow the longish MG34 inside the hull?  Just some thoughts here

There is little doubt that the MG 34 was a superior weapon to the 8mm Breda. Ammunition supplies for the Breda would also be a concern for the Germans. However, after a considerable search both online and through my own books, I am at a loss to find a single photo of any Italian tank in German service mounting a MG 34 for AA defense. I'm not saying it didn't happen, but I sure can't find a photo.

I missed the mark on my question, sorry about that. The machine gun I was referring to replacing was the one on top of the turret, the commanders gun. I wasn't referring to the coaxial. Was not the mg 34 more reliable than the 8mm Breda?

Hmm....Never say never, but it sounds rather unlikely, IMHO. There are photos of a P40 turret which was used as a pillbox in the Gothic Line, sporting a German 7.5cm KwK 37 L/24, thereby setting a precedent for swapping the main weapon on this particular turret, (however, I doubt this was done for performance reasons.)

But swapping out the co-axial Breda for an MG 34 would require at minimum a redesigned and rebuilt mount, with possible modifications to the aperture in the turret. A field-modified AA mount for an MG 34? Easy. Co-axial MG replacement, not so easy. A lot of time and work would be involved for a rather modest gain in performance. I would think the machinists and mechanics would have had more pressing issues dominating their time.