When I bought my clip I went ahead and got one with a 6-speed transmission, the C-160. I figured due to the closer gear ratios it would be more fun to drive in the long run. I knew there was some work involved in getting the 5-speed transmission installed. EricS has a great write up on his site for installing the C-56 transmission. With the C-160 though I have come to discover there is a little more work involved.
With the C-56 you are able to use the selector shaft out of the stock MR2 transmission (C-50 or C-52) by just turning it around, everything lines up (after drilling a hole to let the selector shaft come out the other side of the new transmission). This is not the case for the C-160 6-speed. The two shafts are shown below as well as the reason for the difference, 4 gear selectors, the extra one being for reverse:
Next I disassembled both shafts to see what the exact differences were and what I could and couldn’t use. I then test fit the 20v hardware onto the 16v shaft. Most of it fit except for the extra tab used to select reverse. By test fitting I found out that I could use the 16v shaft with 20v hardware, all I had to do was drill an extra hole in the 16v shaft for the reverse selector. Below you can see how the holes don’t line up:
The next item to figure out was which end cap I would need to use. It ends up I need to use the 20v end cap. It has a heavy spring inside that generates the “toughness” to get into reverse. This created another problem, the 16v shaft is a lot shorter on the end with the cap, so while in 5-6 gears the shaft would not clear the seal on the end cap. But while in reverse it would stick out past the seal. I ended up having the end cap welded to enclose that end while still allowing the shaft to slide in and out.
The selector shaft has now had a new hole added to it for the reverse gear selector. In a test fit the whole assembly seems to work like it should. Test fit shown below. The next step is to seal up the hole drilled (normal for 5-speed swap). After months of sitting around I finally got off my butt and took the transmission to Mazworks to get the hole I drilled adapted to fit the factory shaft seal. The seal fits very nice and looks clean. This is all that I can do to the transmission while it is out of the car, next will be setting up linkage and the mount once the tranny is in the engine bay.