The optional automatic transmission is a JATCO (Japan Automatic Transmission Co., Ltd.) Model L3N71B It is used on all models except the D21-D series truck. The D21-D series trucks introduced in 1986 use a model L4N71B with the Z24i engine, a model E4N71B with the VG30i engine in 1986-87, and in 1988, a model E4N71B for 2wd models with the VG30i engine and a model RE4R01A for 4wd models.
All of these transmissions are fully automatic units, with a three element torque converter and tow planetary gear sets. The transmission shifts gears in response to signals of both engine speed and manifold vacuum.
While it is unlikely that you will ever disassemble the transmission yourself, there are a few adjustments you can perform which will prolong the transmission's life if performed accurately. The most important thing is to change the fluid regularly, which is covered in General Information & Maintenance .