Reassembling the A-series RWD gearbox


This details the final reassembly of the gearbox internals (late model ribcase type). It does not include instructions for reassembling the mainshaft, assembling the 1rst gear or the 3rd/4th gear sliding hub, or how to install the tail extension on the unit. Instructions on the rest of the installation will be uploaded by July 4th 2014. Smooth case gearboxes may be similar in reassembly proceedure. Click on an image to enlarge.

Clean the inside of the gearbox casing, tail extension and all other parts before reassembly Next locate the layger and the two thrust washers shown. The small thrust washer goes at the small end andteh big thrust washer goes at the large end. Now install a new bearing in each end of the laygear, and install the laygear and its thrust washers in the gearbox case. The large end of the layger faces the bellhousing at the front of the unit. Run a coathanger or other thin bar or wire through th elaygear and thrust washers to hold the thrustwshers in place.
Now install the input shaft. The input shaft goes in through the side cover and is gently tapped forward with a hammer and a long punch. Take care not to damage the ceramic coated surface that is part of the synchromesh mechanism. There is a groove cut around the outside of the front of the bearing that must clear the housing so that the circlip can be reinstalled. This is about where the shaft needs to be. Install the circlip and tap the inputshaft back into the gearbox so that the circlip rests against the housing. Now install the reverse gear, then the mainshaft and finally the referse gear shaft. The larger end of the reverse gear faces rearward, and 1rst gear on the mainshaft must be pushed forward as shown in order to clear the reverse gear when installing the mainshaft. Do not install the reverse gear shaft untill the mainshaft is in place.
Alignment of the reverse shaft and the mainshaft bearing housing is critical. Note the peg just to the left of the shaft. This must fit into a hole drilled into the tail extension. It is a good idea to test fit the tail extension to make sure that everything lines up. Once you are sure it is aligned, gently tap the housing into the casing with a small hammer. The slot cut into the reverse shaft is used to turn the shaft if needed when installing it so that the hole drilled into the front of the shaft lines up with the hole in th ebase of the unit. The small plug with a long shaft is used to hold it in place. Be sure to install a new fiber washer on the plug. Now that the gears are all in the transmission, its time to install the layshaft. Bring the laygear into mesh with the mainshaft and input shaft. Next replace the thin temporarty rod with the layshaft, taking care to not drop the thrust washers. Make sure that the end of the shaft that has a small portion where half of it is cut away is at the front of the transmission. Alignment of the cutout is critical, and must match up with the front cover. align it as shown here, and test fit the front cover.

Now fit the reverse gear selector fork as shown. The threaded hole faces down, and the fork fits into the grove at the small end of the reverse gear. This is the reverse selector fork installed. Now install the 3rd/4th gear selector fork over the 3rd/4th gear coupling sleeve as shown.
Next, the 1rst/2nd gear selector fork goes in over the 1rst gear wheel as shown. With the open side of the gearbox face up, install the reverse gear selector rod in through the lowest selector rod hole in the rear of the gearbox casing. Push the rod through the reverse gear selector fork and through the larger hole in the 3rd/4rth gear selector fork.
Push it all the way through the gearbox untill the small hole on the selector rod, lines up with the threaded hole on the selector fork. The locking screw and nut can now be installed through the drain plug hole in the base of the gearbox A view through the drian plug hole with the lock screw in place.
Back off the nut untill its agains the head of the screw, and then tighten the screw with an 11/32" socket. You may need to wiggle the slector rod untill the screw goes in all the way. Finally tighten the nut against the fork with a 7/16" open end wrench. Now install the plunger (factory part number 2A 3110) in the hole in the center of the rear of the side cover flange. This plunger is shaped a bit like a pill, rounded off at both ends.It is much largerthan the similarly shaped plunger 22G89. Drive the plunger all the way in and move the reverse selctor rod if necessary so that the plunger is as far in as it will go. Plunger 2A 3110 acts as an interlock that prevents both first and reverse from being engaged at the same time.
Now insert the 1rst/2nd gear selector rod through the top selector hole in the rear of the gearbox casing. Line up the hole in the rod with the threaded hole on the 1rst/2nd gear selector fork and install the locking screw and nut just as with the reverse gear selctor fork. Now push the 3rd/4th gear selector rod in the remaining selctor rod hole in the gearbox casing.
Push it through the selector fork, but don't push it all the way through just yet. Drop a ball (factory part number BLS 110) in the hole on the lower front corner of the side cover flange. Push it all the way in, and move the reverse gear selector fork, untill the ball is clear of the 3rd/4th selector rod hole. Turn the gearbox over so that the drain plug faces up, and drop a ball in the upper of the two holes shown. Drive the ball all the way in and adjust the 1rst/2nd gear selector rod untill the ball clears the 3rd/4th gear selector rod hole.
Here is a cross section of this assembly. The balls are interlocks, designed to prevent more than 1 gear from being selected at once. Now push the 3rd/4th gear selector rod all the way in. Line up the hole in the rod with the threaded hole in the fork and install the locking screw and nut just as with the other forks. Turn the gearbox so the drain plug faces up. Install the plunger (rounded end first) in the lower of the two holes shown.
Install the long shanked plug (factory part number 2A 3253) in the upper of the two holes shown. Make sure to use a new fiber washer. Next install the spring in the hole you put the reverse gear plunger in, and then the short plug (factory part number 6K 643) along with a new fiber washer. Now install the two plungers (rounded edge first) in the two front holes on the front edge of the side cover flange.
Clean the side cover flange and install the two springs as shown. Carefully install the paper gasket. Install the side cover using eight 1/4"-28 UNF nuts, eight 1/4" lock nuts and a 7/16" socket or wrench. Thoroughly clean the inside of the bellhousing (especially where the gasket goes), and install a new gasket. carefully measure with a caliper or a micrometer how much the front bearing sticks out of the casing, how deep the recess in the front cover is, and how thick the gasket is. Add together the depth of the recess in the cover and how thick the gasket is and subtract this from the depth of the recess in teh front cover. This is how thick the shim needs to be. 0.006" is common
Install the front cover. The shim goes between the outer bearing race and the front cover. make sure the shim is centered on the bearing race, or damage to the shim or front cover could result. Clean the back of the casing thoroghly. Install the paper gasket, and pull the 1rst/2nd gear selector back so that 1rst gear is selcted. The rear extension can only be installed with the gearbox in 1rst gear. It is not possible to geat the conrol lever (factory part number 22A 476) to engage the selector rods unless the gearbox is in 1rst gear. Next install the tail extension. You will need to twist the extension a little and wiggl ethe control lever to make sure it gets in teh selctor rods correctly.