I have a 79 911SC 5 speed manual transmission. Vehicle will not go into 1st gear with or with out engine. All other gear work fine. Checked linkeage and shifter coupling. Any one have any idea what my problem is? Thanks

 

is it only first gear ? if so it is likely a damaged gear set. synchro ring or dog teeth. But regardless it sounds internal if your other adjustments have been verified.

I am assuming all other gears are fine so that would eliminate the clutch release bearing and fork.

 

Could not tell if you have recently lost 1st gear or did some maintenance to coupler, bushings, etc.

Im not mechanic or engineer, but I replaced couplers in 2 Porsches and found the linkage to be very sensitive regarding getting all the gears to line up properly. Just the slightest adjustment is needed to find all gears. I recently changed out coupler on my Weissach, and finally got my mechanic friend to find all the gears for me, and its shifted perfectly ever since.

Not sure if bad bushings would cause your issue, but very inexpensive parts and fairly simple to change out.

Good luck.