Long post ahead. I've made a ton of progress on the transmission since I last updated this.
Installed the rear bearings and finished the gear/shaft assembly last week. Getting everything ready for the next level of assembly:
Shift rods, clutch forks, etc. installed. Ready to install the intermediate housing:
Intermediate housing on, shift rod ends installed, and speed drive gear in place Ready to install bell and extension housings.
Bell and extension housings assembled.
Front bearings installed...
...and covered.
Finished...
...or so I thought. After the silicone cured I decided to slap on a stock shift lever and test out the gears again. I quick row from 1-5 to neutral and everything checked out. Wetn to test reverse I found I couldn't get it to engage. I checked the other gears again and all were locked out. A quick spin of the input shaft told me it was already in reverse! I pulled the extension housing (and all it's pieces) off and discovered somehow I managed to shift into reverse while going from 5th to neutral. This morning a quick internet search showed this is quite common in Miatas and RX-7's though I'd never heard about it. Apparently this spring:
on the front of the 5th/reverse shift rod puts a good amount of force in the reverse direction. Shifting too quickly from 5th into neutral or too slowly from reverse into neutral seems to be the primary causes although some have reported this is worse with worn shifter bushings. I'm guessing what happened to me was when I released 5th gear into reverse (didn't 'guide' it) the force of the spring boosted the forward momentum of the rod, which somehow carried it into reverse at the precise moment I moved the selector rod into neutral. It probably didn't help that I had only 1/2 the shifter bushings installed and that the transmission was vertical so gravity was acting in reverse's favor. What's most annoying is there is a fix that can be done without removing the extension housing involving a screwdriver through the reverse switch port. Had I waited a few hours I would have discovered this and not had to remove the extension housing and associated pieces. Now I get to scrape off all the silicone and go through that process again. Either way, the transmission is essentially done so it'll be time to move onto the next task soon.