ZBUM's Nissan Z31 300ZX Transmission Information Page
The Z31 came with three different manual 5 speed transmissions. All manual non-turbos used a 5 speed Nissan transmission (FS5W71C) which is quite reliable. The 84-86 manual turbos used a Borg-Warner T-5 5 speed (FS5R90A). The 87-89 manual turbos are internally, the same as the nissan transmission found in z32 turbos, trucks, pathfinders, etc (FS5R30A). All manual transmissions have synchros on all forward gears. If you change the gear oil in your transmission on a semi-regular basis it should give you absolutely no trouble at all. That is, provided you don't beat the poop out of it.
Automatics suck, but there are some people who still insist on buying them. All automatic Z31s used the 4N71B transmission. Change the fluid every so often, and check the level every time you change your engine oil. Also, if you overheat your car for whatever reason and it has an automatic, CHANGE THE TRANSMISSION FLUID IMMEDIATELY!!! If you don't, your transmission will blow up as a result of the fluid getting overheated in the cooler and burning inside the transmission, and this is bad. Of course, you could avoid this by putting in a manual transmission, and have more power and economy to boot! The overdrive switch in the automatics has a temperature sensor that does not allow the transmission to shift into overdrive until it is sufficiently warmed up to avoid possible damage. Level 10 makes an upgrade that will allow your transmission to hold 500+ hp. Click here for more details.
All Z31 transmissions are completely interchangable. They have no problems bolting up to the motor. One problem is they don't always mount to the body correctly. You may have to drill and tap new holes for the transmission mount. Another problem comes in when you try to mount the driveshaft. Each transmission has it's own output shaft size and overall length. Finding the appropriate driveshaft for a two seater is no problem. Just find another two seater that had the same transmission and take that driveshaft. If you have a four seater, you're going to have a more difficult time. Only in Canada did the North American market get a turbo four seater. And almost all of them were automatics. So you'll need to find the appropriate driveshaft for the transmission you just bought and have the driveshaft lengthened. If you get a FS5W71C, there are plenty of 2+2 5 speed models around.
The only thing left is to determine if your differential companion flange is correct for the driveshaft. The 84 to 86 had a different style than the 87 to 89 models. If you swap to the NA transmission, find the appropriate driveshaft for your year to save money. If you go from the FS5R90A (T5) to the FS5R30A (Nissan Turbo), you will also need to buy the appropriate companion flange.
There are several different manufacturers of lighter flywheels for the Z31. The non-turbo and the 84-86 turbo came with a 240mm flywheel. The 87-89 turbo came with a 250mm flywheel. This isn't the overall diameter of the flywheel, it is the diameter of the clutch surface area. The overall diameter of the flywheel is the same. Different manufacturers have made these different ways. Some will include the different mounting holes for the different sized/spaced clutches. You can use any Z31 flywheel in any of the manual transmissions. Just be sure you use the appropriate clutch. Be aware that using some of the FS5R30A clutches on the other transmissions may require you to grind down some of the inside of the transmission bell housing to fit properly.
Transmission Fluid Levels:
Fluid Temperature Ratings: