Swapping a 5 speed tranny into a 1600. Not a hard swap as swaps go but removal of the engine and tranny is a must. You might want to replace the clutch while you have the motor out. I prefer the 2 liter clutch over the 1600. It requires a bit more pressure on the clutch pedal but is more robust than the 1600 clutch assembly.
A tranny swap requires additional parts besides the tranny. You will need the 2 piece 5 speed driveshaft and the 5 speed transmission mount that bolts to the crossmember plus the shift plate cover for a 5 speed. You should also get the 2 liter backing plate that goes in between the tranny and the motor. There is a big difference between the R16 with the 2 liter being thicker. If you use the R16 backing plate you will be putting undo pressure on your crank thrust bearings and will eventually damage them along with the engine. I know that from experience. I was lucky as we were troubleshooting an oil leak and I had pulled the motor. While at the machine shop they noticed the damage. The solution then was to have the pilot shaft removed from the tranny and turned down a few thousands to relieve the force. You cannot mix 4 speed forks and throw-out bearing collars with the 5 speed. Use the 5 speed parts and you will have no problems. Also you can use the 1600 speedo cable minus the angled piece that mounts to the tranny. Someone else recommended using a 2 liter speedo cable but I had no problems using my 1600 speedo cable. After you have aquired the correct parts it is simply a matter of bolting the 5 speed up, cutting the transmission tunnel to accept the five speed shift lever, reinstalling the motor, and adjusting the clutch. It is pretty straight forward.
NOTE: The early cars i.e. 65 thru 67 may require some additional rework to the tunnel where the speedo cable connects to the tranny. Careful measurements will give you an indication of where you need to bang the tranny tunnel out a bit. Using the R16 90 degree angle speedo adapter is also a requirement for the earlier cars. Thanks to Fred Katz and Datsunmike for pointing these facts out.
It is probably a good idea to either go through or have the tranny gone through before installing the unit. 5 speed transmissions are known for their 5th gear neutral syndrome. The early 5 speed 5th gears used a nut to hold the 5th gear in place. If this nut works loose you have what is called 5th gear neutral with no 5th gear available. Several of the vendors sell a repair kit for this or you could weld the nut in place. Just something else to be aware of concerning the roadster 5 speeds.
