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All T18's are basically the same. The following will allow you to rebuild this transmission while adding an adapter.

• Remove top cover, front bearing retainer and rear housing (2 or 4 wheel drive versions). Early "2" lever type units (identifiable by the rectangular top cover) have a tapered pin that retains the reverse shift fork located on the left side of the unit. Locate and drive this pin out from the front of the transmission with a small punch. Tap the pivot, that is retained by the pin you removed, out from inside of the unit. Now remove the lever. The later T18 has 3 aluminum levers.
• Remove snap rings from both front and rear shafts that retain the bearings. Using a puller remove the front and rear bearings. Let the front input (maindrive) hangout through the front of the unit. Lift the mainshaft (output) forward and up through the top of the case. Note that there is a thrust washer on the front end of the mainshaft. This is for the loose needle bearings in the maindrive to thrust against. DO NOT lose this washer.
• Remove the front shaft up through the case. Remove the flat retaining plate (rear of case) that is in-between slots in the counter shaft and the reverse idler gear shaft. Note the location of the "slots" on both shafts and the direction they are pointed. They must be the same when reinstalled. Drive the large countershaft (cluster gear) from the front of case out through the back of the case. Drive the idler gear shaft out the same direction from inside the case.
• Clean, dry, and inspect all parts. Grease the bearings or bushing inside the idler gear and reinstall the shaft making sure the "slot" is the correct direction. The cluster gear has 2 rows of loose needle bearings, 4 washers, and a sleeve. There is a thrust washer at the front of the cluster gear and a trust washer and spacer at the back of the cluster gear. Use heavy grease to hold the needle bearings in place inside the cluster gear with the small washers in between the rows of needle bearings and at the end of the needle bearings where they are exposed on both ends of the cluster gear.
• Use the heavy grease to hold the front thrust washer against the case. Slip the rear shaft into the case with just enough of it protruding inside to hold the spacer and the rear thrust washer in place. Gently roll the cluster gear into position between the thrust washers and drive the large pin through the case. Check the direction of the "slot" before moving the shaft. Install the retaining plate between the 2 shafts.
• Remove the gears form the mainshaft (output) taking careful note of how they are stacked. DO NOT ATTEMPT TO SLIDE THE 1ST REVERSE GEAR (big straight cut gear) OFF THE SYNCRO HUB. There are 3 balls with coil springs under this gear and they will fly out and either hurt you or get lost. If you have to replace this gear you can use a couple of long metal gear driven hose clamps by clamping them over the three syncro dogs (plates under the sliding low and reverse gear). This will keep the parts from flying. Clean and dry the parts.
• The mainshaft you are going to use must be clean (this will be the adapter shaft if you are using one). Make sure that the 3rd gear thrust is the same on both original and new shafts. Some use a snap ring and thrust washer others have the thrust built on the shaft. If this is the case DO NOT try and use your old thrust washer. Install all gears and syncros on the new shaft.
• Using heavy grease, install the needle bearings in the maindrive (input gear). Put it in the case allowing it to hang out of the front. Tip the mainshaft with gears up so that you can slide it into the case. Grasp the front maindrive and the rear mainshaft and push them together. Make sure the small thrust washer is in place and the 4th gear syncro ring is lined up with the 3 notches engaged with the syncro "dogs". Drive the front and rear bearings onto both shafts. The narrow bearing (20mm, some T18's use a wide 23mm bearing that is the same as the rear bearing) is the front bearing. Install the snap rings. If you have the reverse lever that goes in using the pivot (early style T18) install it now. Use a gasket sealer on the gaskets that are between the front bearing retainer and the rear adapter housing. Install and tighten bolts and or nuts. If you have the 2nd design 3 lever cover make sure the nylon fork pads are inplace on all 3 levers. Use the gasket sealant for the top cover gasket and install the top cover. Make sure that the transmission is in neutral. Line up the shift forks and bolt the cover down. It is ready to install.