Yet another 904 rebuild thread, what kit?

Break out your digital calipers and measure the grooves in the frictions. I did. Grooved frictions have 20% LESS surface area than smooth ones. That means that 4 smooths have the same contact area as 5 grooved. But stock smooths are weak and they're too thin for third gear heat. The stock third gear frictions are thicker and grooved because the factory material can't take the heat, shifting at 6k rpm; whereas the forward clutch with its thins; is engaging at under 1k rpm. The solution is to run smooth thin .061 Red Eagles in both drums. You can add an extra plate plus get rid of the grooves in the third gear drum. It's like running six frictions instead of four. That kit is for dummies.