911SC Won't go into 5th
 

Driving my 83 911 SC Targa today and it refused to go into 5th gear. I've had the car about 7 years and have, in the past, on occaission have had difficulty coming out of 5th gear. It has not happened in several years and only happened a few times when I came to a stop with clutch in but NOT downshifting to neutral until I was at a complete stop. I am thinking the shift coupler???

yes, or shifter bushings

Not sure what you're saying, but you should always remove the transmission from 5th gear, with a downshift to 4th, BEFORE you slow to below 55-60 mph. Your technique must be changed to solve the coming out of 5th issue.

Going into 5th is another matter entirely, and could be anything from a shift tower problem, to a bushing problem, to a coupler problem, or an adjustment problem. It's even possible that the shift rod in the tunnel is failing. Hands-on diagnosis is required for a problem like yours.

915 trans problems
 

I have a 1981 911sc so we have the same type 915 transmission. I have experienced difficulty with my shifting also. I cannot go into 1st unless the car is completely stopped. Even with the clutch engaged I can feel the gear teeth grind as I try to engage the gear. Also, I can shift into 5th, but I cannot downshift into 4th unless I go to neutral first, rev it a bit (double clutching) before entering 4th gear.

The problem is the synchros are bad. I have a great friend who is a trans expert and that's what he told me. Also, other research has brought me to this "synchro" conclusion. I only drive the car about 500 miles a year so I haven't fixed this problem on my car. I figure a 915 trans rebuild is $1,500 to $2,000 from a local shop (or maybe $2,500?). You could most likely save money if you buy the rebuild kit beforehand from Pelican or another good reputable supplier. It might save you "parts mark-up" from the shop. I also see complete good used transmissions for sale at nationwide dismantler shops.

So I guess the question is to spend some money or deal with the quirks.
By my own admission, however, I am not an expert.
"And that's all I have to say about that."

use a new shift coupler first. This drastically improves shifting if adjusted right, Its a pretty easy DIY

Replace the pin screw in there too, ask me how I know

Any issues with going into reverse?

Nope Seems to go into reverse fine. I ordered a new coupler and related parts from our host. Car gets detailed Monday, parts arrive tuesday, Friday to Amelia Island!

OK. I replaced the coupler. The old one seemed to be ok visibly. I adjusted the coupler and shift rod and still couldn't get it into 5th. No grinding, just resistance. Re-adjusted the shift rod. Now it wasn't any longer in 1st. No acceleration and clutch burn smell. Played with adjustment a bit more. Went for a drive and shifted into all gears fine! But only at low speed as there was rush hour traffic. I noticed that downshifting into 4th, even at lower revs resulted in a grinding sometimes. Waiting a moment or double clutching was fine. Also downshifting into 2nd was a little difficult at times(but that has been a quirk for 7 years-a little worse now. Took a better drive today at highway speeds-sometimes I can get into 5th, sometimes I can't...I didn't notice any clutch odor until I lifted engine lid to check oil level. It was faint so I figure it is left over from yesterday?

What about the bushings at the shifter end? Have you checked them?
There;s a lot of possibilities here but always best to start with the easy external things.

I had a similar problem - completely lost 5th gear in my '86. I followed the adjustment procedure, but couldn't get all of the gears to work at the same time. The problem turned out to be the shifter rod bushing in the tunnel. It was in pieces on the floor. I replaced it and the shifter adjustment procedure worked perfectly. Now it shifts fine.