I ordered a 1980 Brake MC from advanced. They sent me one that had no marking noting size like the old ones do. It looks a little bigger than the old one any easy way to tell if it is 15/16" . I crossed the part numbers with the 240z and it was different .

You may want to post a pic so we can tell what you are looking at.

You can measure the bore easily before you fit the MC to the brake booster. You can also see the difference if you hold them side by side and look at the plungers where they fit to the brake booster. There is almost 2mm difference in diameter.

Chas

Thanks chas . I think that's it . About 2mm is it . I thought they were not being made any more . I guess this a reproduction .

Dc