Today I worked mainly on tearing-down the transmission. The car has had a bad habit of popping out of 1st gear (unless you hold the shifter in position). In fact, that's why I got such a good deal on her. Before mating the adapter plate and electric motor (and the new clutch I just got) I wanted to tear the tranny apart and see if I could diagnose and fix the problem. A good alternate approach here would be to just buy a new/used tranny, but I want to see whether I can fix it myself first before taking that route.
The shop manual has a very detailed description of the teardown/rebuild procedure, but again, I'm finding that my car is different from what they describe in a lot of details.
I also found a very helpful article on the subject at www.miata.net.
The first phase of this project involves removing the transmission "guts" from the casing. The casing consists of three sections: bell housing, middle part and rear (which includes the shifter turret). I followed the suggestion of the article referenced above and used a bolt through a 2x4 to push the works out of the bell housing. Unfortunately I followed the shop manual's instructions on removing the input shaft snap ring prior to pressing the parts apart. A tremedous amount of pressure was applied and the thing barely budged. I found that the jack shaft was completely locked up and even after I backed-off on the pressure things only turned reluctantly. The snap ring that actually needs to be removed is the big one that retains the outer race of the input shaft bearing -- then everyting presses out nicely with minimal force.
Here's what a naked 5-speed transmission looks like.
This is a closeup of the dog teeth for 1st gear.
This is a closeup of the same area for 2nd gear. I don't see an appreciable difference.
Another view of 1st with the selector moved so you can see the synchronizer.
Next, you drive a roll pin out of the selector fork and remove the shifting rod. (Actually, the selector fork was removed -- for visibility -- already in the pictures above.
While I was tapping out the shift rod for 1st/2nd a little curled-up piece of metal fell out on the table -- actually two of these came out.
In order to get the shift rod out, you remove the ball detent that locks the rod into one of three positions (for 1st, disengaged, and 2nd). I had to turn the tran upside down and tap a bit to get the ball to come out of the hole, and when it did, it was followed by these little guys. I think they live in the space between the 1st/2nd rod and the 3rd/4th rod...
(Note: After closer inspection, the thin pin passes through the 3rd/4th rod, there are actually two of the thicker guys that live on either side of the 3rd/4th rod -- collectively these things prevent any of the rods from moving unless the other two are in the "disengaged" position. It's a pretty ingenious setup.)
Beginning to remove things from the tail end of the main shaft.
Not shown: the drive gear for the speedometer -- since the speedo is now a Hall effect sensor, not a cable that snakes its way up to the speedometer in the dash, this is fairly stupid design (although it was probably cheaper to do it this way).
With the speedo gear out of the way, we next remove a snap ring, a washer, and a pair of "C" washers that are surrounded by a retaining ring. The "C" washers have a sharp and a more rounded edge -- sharp faces the bearing.