Either I'm not understanding what you mean, or I'm missing something. Let's take a typical gearbox like the one below. It's directly coupled to the engine, and its only external rotating part is the flange at the bottom, to which the shaft is connected. If you put the tape on that flange, or on the shaft connected to it, you certainly can measure the rpm, but with the two caveats of my post #13: 1) you can't check idle speed with gear disengaged 2) the rpm that you measure is affected by the g/box reduction ratio Mind, as I said I normally attach the reflective tape on the pulley, so the gearbox and its layout is totally irrelevant. In just one occasion, when the very tight space on the front side of the engine did not allow to keep the photo tach in a decent readable position, I attached the tape to the g/box output flange. I did have to consider the reduction ratio for calculating the actual engine rpm, though. If there is a third alternative (vs. either the front pulley or the g/box output), I'd be curious to understand what it is.