915 shifter moves to "5th" but doesn't always change gear.
 

Anyone have ideas or suggestions about what might going on? 143K mi. Had worn 1st & 2nd synchros replaced at 90K. No problems since then. Changed fluid recently. Filled until fluid spilled out. Worked perfectly until yesterday.

How does the shift coupler look?

I actually haven't taken a look yet, but that is the place to start I suppose.

With no recent changes to the coupler I would check the ball cup bushing. It sits below the shifter and connects the shifter to the shift rod. They dry up and crack with age and will make the shifting loose and not allow the shift rod to move to the correct positions. I would check the coupler as well. It could need to be replaced or just adjusted. I put masking tape on the coupler/shift rod to make it easier to know how much I moved it.


Porsche 911 Shifting Improvements | 911 (1965-89) - 930 Turbo (1975-89) | Pelican Parts DIY Maintenance Article

Fig 2 shows the ball cup bushing

+1:)

Also lift the boot or cover and see where the shifter falls in neutral, maybe to aft?

Recently helped buddy replace his bushing at the shifter and we found his shifter was to aft not allowing it to get into gears.