If you have read the original 5 Speed 101 you know that it was compiled from a series of posts to the XANA forum on the SeattleX1/9 page. At the time I wrote it I had no idea that it would evolve into a single document hosted on several sites, including SeattleX1/9. With that in mind I thought it a good idea to write the 4 Speed 101 supplement as a single document for ease of use and readability. This supplement is not intended as a stand alone piece. It is written, as is titled, as a supplement to 5 Speed 101 therefore if you are undertaking such a project you will want to start with 5 Speed 101 and then read this document. 4 Speed 101 will only document the differences between the 5 speed and 4 speed transmissions and there will be many references to 5 Speed 101 so referencing it will be a necessity.
First, the differences in the 4 speed and 5 speed are few but significant. The most obvious difference, other than the lack of a 5th gear, is the CV axles. The 5 speed has modern, external CV joints that are separate components where as the 4 speed CV axles incorporate the inner CV joints in transmission’s differential and the outer CV joints combine the cup and stub shaft as a single piece. Internally, the two transmissions are very similar in architecture but there are differences in individual components. Obviously, the 4 speed will lack the 5th gear extension housing and gearset. These are the primary points that we will be dealing with. For the remaining information, 5 Speed 101 will apply.
Removal: Pulling the 4 speed is the identical process to the 5 speed with the exception of dealing with the half shafts. Instead of CV joints, which can be unbolted from the transmission’s stub shafts, the 4 speed inner CV joints ride inside the transmission case on a tripod carrier inside the differential. The axles pass through a rubber boot (often called a ‘gator’) that retains the gear oil. As in 5 speed 101, break the axle nuts loose, set the car on jack stands, remove the rear wheels and drain the gear oil. While working from above, remove the carb fan and hose and the clutch return spring from the clutch slave cylinder’s mounting bracket. The spring is quite strong so effort is required. I use a large pair of pliers and a big screwdriver to pry one end off. Next, unbolt the slave cylinder bracket from the transmission case. There are two 13mm bolts that hold it to a flange on the top of the transmission and a single 13mm nut on the end of a case stud at the other end. Once these are removed the slave and its bracket can be tucked out of the way behind the coolant tank. Next, break the two top bell housing bolts loose but do not remove them.
Working from under the car, unbolt the starter but do not remove it, unplug the reverse light switch and remove the splash panel from the left side inner wheel well. Now from the left side wheel opening, remove the axle nut and the brake caliper and tie it out of the way, then remove the three 10mm nuts which retain the half shaft boot to the transmission case, slide the boot back and turn the axle so that the tripod bearings align with the cutouts in the case opening. Next, remove the two 17mm bolts that attach the lower strut mount to the upright, swing the a-arm and upright down while pulling the half shaft out of the transmission. Finally, pull the half shaft out of the upright and lay it aside. Before laying the half shaft down, slide the rubber boot back over the tripod bearing to protect it. You may also want to wrap it with a clean shop towel.
From underneath the car, break the two lower bell housing bolts loose (one is by the starter and the other, usually a stud and nut, are by the left side axle), then place a jack under the engine oil pan to support it and remove the cross member and transmission mount along with the stamped steel backing plate/dust cover behind it. Next, remove the three 10mm nuts that retain the right side half shaft boot to the transmission case, slide the boot back and turn the axle to align the tripod bearings with their cutouts as you did on the left side. And as on the left side, remove the right side axle nut and brake caliper, unbolt the upright from the strut; swing the a-arm and upright down but this time pull the outer CV joint out of the upright. Once out, the entire half shaft can be pulled from the transmission. The rest of the removal is as documented in 5 Speed 101.
Disassembly: Disassembly of the 4 speed is much like the 5 speed once you are past the 5 speed extension. With the transmission on the bench, as with the 5 speed, first remove the three 13mm case bolts from inside the bell housing, then lay the transmission with the bell housing down. Now remove the six 10mm bolt that hold the end cap to the main case. You may need to tap the back side of the tab at the edge of the endplate to get the cap to come loose. Once it is off you are looking at the end of the driven and lay shafts and their bearings. Note that the bearings are retained on the shaft by a pair of snap rings instead of the 5 speeds 30mm nuts and there is another snap ring on the outer edge of each bearing that retains it in the case. Use a pair of flat nosed snap ring pliers to spread the outer snap rings that retain the two bearings. Once the snap rings are spread, a screwdriver can be used to pop them out of their grooves. Do not attempt to remove the snap rings that retain the bearing on the end of the two shafts. Next, remove the two 13mm bolts that retain the detent ball plate from the side of the case next to the reverse switch. Remove the springs and use a pencil magnet to retrieve the detent balls from their holes. Next, remove the 13mm case bolts that hold the two main case halves together and the cases can be separated just as the 5 speed. Note that, unlike the 5 speed, there are no stub shafts that must be removed before the cases can be separated.
With the cases separated the gearclutster and selector rods are exposed. The selector rods and shift forks can be removed, along with the driven shaft and lay shaft, just as described in 5 Speed 101. The procedure is identical. Once you have the two shafts out its time to disassemble the lay shaft (the lay shaft is the shaft that contains the main gearset and pinion gear). To disassemble the gearset it is necessary to remove the snap ring that retains the bearing on the end of the shaft. Note that the snaping also retains a pair of bevel washers that preload the gearset. Care must be taken when removing this snapring to avoid it going flying and injuring you. I use a heavy leather glove on my left hand covering the end of the shaft with my palm while using my fingers to hold a flat nosed punch against the inside of the snapring’s eyelets. I then use a hammer to gently drive the snapring out of its groove. I work gently on each side to drive it out evenly. It only takes a few light taps and the snapring will pop out of its groove releasing the bevel washers with a considerable pop. While working our the snapring keep your gloved hand over the end of the shaft to capture the snapring should it pop out. The snapring and bevel washers can now be removed from the end of the shaft along with the gearset. In many cases the bearing and gearset my be stuck on the shaft. They are easily freed by the same method described in 5 speed 101. Once the gearset is loose, remove each component and lay it aside in order as per 5 Speed 101.
Inspection: The 4 speed inspection process is identical to the 5 speed as documented in 5 speed 101. However, there are two important differences in the 4 speed and 5 speed gearset components. First, on ’74 through mid ’78 4 speeds, the 3rd and 4th gear synchronizers and slider are smaller in diameter than the 5 speed. Later ’78 4 speeds have the larger diameter synchros and slider as used in the 5 speed. This is important when ordering parts. They are easy to tell apart, the early 4 speed 3-4 synchros are 2 and 5/8th inches in diameter while the later style (as used in the 5 speed) is 3 inches in diameter.
The second difference in the 4 speed gearset is the 1st and 2nd gear slider. Specifically, the lay shaft reverse gear is the outer teeth on the 1-2 slider. On the 5 speed these teeth are positioned below the groove for the shift fork while on the 4 speed the reverse teeth are located above the groove for the shift fork. The reverse teeth must be inspected for damage just as in 5 Speed 101. Inspection of the other gear cluster components is identical to the 5 speed.
Re-Assembly: Restacking the gearset is as described in 5 Speed 101 with the exception of the 1-2 slider which must be installed with the reverse teeth positioned above the shift fork groove. The slider can be installed upside down but reverse will be non-functional. The exception to the 5 speed assembly process is the installation of the 4 speed’s two beveled washers and snap ring. After fitting the end bearing on the shaft, stack the two beveled washers with their outside edges against each other and fit the snapring on the end of the shaft (a new snapring is preferred). It is necessary to compress the beveled washers to seat the snapring in its groove. To do this, remove the snapring and bearing from the end of the input shaft and fit the bearing over the end of the lay shaft above its snapring and beveled washers. Next set a ½ inch drive, deep well socket (30mm works well) over the end of the shaft so that the edge of the open end of the socket sits on the inner race of the bearing. Next, insert a bellhousing bolt through the socket and thread it into the end of the lay shaft. Now use a 19mm wrench to tighten the bolt and compress the beveled washers. While doing so, turn the shaft so you can see the gap in the snapring and use a penlight to see when the snapring aligns with its groove in the shaft. Once the snapring and groove are aligned use a thin flat blade screwdriver and a hammer to gently drive the snapring into the groove. Work your way around the snapring finishing on the back sides of the eyelets to drive them together. Once the eyelets are closed nearly together, remove the bellhousing bolt, socket and bearing and inspect the installation of the snapring. Ensure the snapring is fully seated by using a flat nosed punch and hammer to further seat the snapring as necessary. When fully seated the two eyelets should nearly touch.
Installation of the gearset, selector rods, forks and linkage are identical to the 5 speed with the exception of the lack of the 5 speeds 5th/reverse interlock mechanism that fits under the intermediate linkage. Re-assembly of the case is the reverse of the disassembly process described above or similarly in 5 Speed 101. The same is true for re-installing the transmission in the car.