Occasionally can't get 915 into 3rd.
 

I have an 86 915 gear box that was rebuilt by a local shop. I didn't install it until a couple of years later, so it's out of warranty. Sometimes shifting from 2nd to 3rd, it will not go into 3rd. I have to shift back to neutral, move shifter to the left (1st,2nd plane) and then try again. Usually doing this once or twice and I can get it into 3rd. Sometimes it goes right into 3rd without this ritual. Any idea what might cause this?
I have tried a Rennshift and stock shifter with the same issue.

Sounds like your coupler is out of adjustment
Ernie

2nd for coupler is either toast or needs adjustment. Take a look under the panel behind the seats.

How many miles on the rebuild....I had a similar balking issue on a rebuild that went away once 'broken in'...you are probably mixing new/old and it takes a bit to bed in. Mine was a second gear deal.
I would check the adjustment as advised too.

Only a couple thousand miles since the rebuild. It's a 915/916 914 setup with a 3.2. So there is no coupler. Just an adjuster under the center console that allows me to make adjustments. I tried every possible adjustment and the issue is still there. To much one way and I lose 5th and reverse. Too much the other way and I lose 1st and 2nd. Otherwise I can get into all the gears, with the way it's adjusted now.

I had the same issue on my 915. It turned out to be the internal selector forks had not been set correctly. I found the issue after I rebuilt the box myself after a previous rebuild a few years ago.

On my box there was insufficient separation between the two selector forks so essentially I was trying to engage two gears at once. With correct adjustment this issues is completely fixed.

I also spent much time adjusting the shaft coupler thinking it was this......

See this thread:

http://forums.pelicanparts.com/porsche-911-technical-forum/921412-having-trouble-adjusting-shift-forks-915-transmission.html

/\ this - I had the same issue, changing the coupler eliminated it.

There is no coupler on this car.

Thanks everyone for the help!! At the firewall i'm running the PMS shift rod bearing. A pretty precision setup, but has no slack.
914 Gear Shift Rod Bearing Kit - (1970-1976) PORSCHE 914-6/4 - Fire Wall / Bulk Head By Patrick Motorsports Porsche & Mid Engine Performance Specialists
I thought about removing it just to see if it would help. I'm leaning towards SUB8's conclusion, since I have no coupler and have fooled around with the side to side and fore and aft settings, to no avail.