Note: before I get into the next disassembly step I want to address a difference between transmissions that may be encountered. Some transmissions, specifically S5 N/A transmissions, have a very large nut, weight, and c-shaped, wedge spacers on the mainshaft just in front of the speedometer drive gear. My understanding is this was added to damp vibrations caused by the higher engine speeds in those cars. I chose to go with the Miata mainshaft and forgo this weight at the recommendation of Mazdatrix who has been using this setup in their race cars for years without issue. If your transmission has these parts they're easy to remove (I used a large, adjusting wrench) but make sure you keep everything organized for resassembly.
Before the 5th/reverse gear housing can be removed there are some obstacles that must be cleared. Starting at the back the first is the speedometer drive gear. It's held in place with two snap rings.
Remove the rear snap ring and slide the gear off the mainshaft. Be careful not to lose the steel ball underneath that prevents the gear from spinning independently of the mainshaft.
Speedometer drive gear, snap rings, and steel ball:
Assembly note: there is no forward or rear on the drive gear. It can be reinstalled either way.
Next are the shift rod ends. Each of these is held in place with a roll pin. Using a hammer and punch drive out each pin and slide off the rod end. Start with 1st/2nd:
Next is 3rd/4th:
Last is 5th/reverse:
Assembly note: when reinstalling the roll pins make sure the "break" is facing forward or rearward (parallel to the axis of motion). This also applies to the roll pin in the control rod end removed earlier.
With the rod ends removed there should be nothing remaining in the way of the 5th/reverse housing. As with the extension housing and bell housing this is sealed to the bearing plate with RTV. Apply alternating taps with a rubber hammer and it will break loose. Slide it off the mainshaft and the "guts" of the transmission are completely exposed.
