993GT

OP, if it's largely load based, my new first suggestions would be now trans mounts and cables at the trans (make sure they are fully clipped in)

docboy, yes that's the pressure plate

mdkelly1

Yes, it's the pressure plate. You can see the three cracks in the "diaphragm." In the old days with American muscle cars, it (they) looked more like "spring fingers," but the function is the same, to enable clutch engagement/disengagement.

In this particular case, the car was slightly hard to shift from third to fourth under moderately hard acceleration, but it wasn't necessary to force it into fourth, just a little difficult. As Kevin points out, continued use with this condition, especially when trying to "force" the shift will take a toll on the synchros.

This pressure plate diaphragm probably had a single crack in it for some time, before completely failing from the additional strain placed on it resulting in the two additional cracks. It failed in a hotel parking lot (while parking), at Daytona during the PCA Race a few years ago. By failing, I mean that the clutch would not disengage and you could not shift into or out gear while the engine was running due to the broken diaphragm.

As you might imagine, it made for some interesting maneuvering to get it out of the parking space in a tight parking lot and onto a flatbed. This failure is not necessarily an uncommon problem as Kevin points out. Other owners have encountered it as well. You can find a few threads on it in some of the forums.

It is interesting to note that the clutch disc was in excellent shape with lots of life left and could have been reused. I put a new one in, along with a new pressure plate, clutch fork, throw-out bearing, etc.

I don't know if it is the cause of the OP's hard shifting issue, but it is something to consider.

my04996tt

Seeing those pics of cracks am surprised it didn't break up completely. Hope I have to deal with that.
Last night I checked trans mounts, they look solid/tight, trans cables also are fine. Clutch engages and disengages smooth with no noise. Tonight will check hydraulics and slave cylinder. Since it was my 1st time inspecting the bottom of the car was glad to see everything appears dry and really clean.