How-to, Part 2: Assembling the AX-15 Transmission and Final Details

     Once you have cleaned and inspected pieces, order the necessary new parts. In the AX-15-93 illustration (below), these are the “must renew” items, each replaced during a thorough manual transmission rebuild—this unit had over 200,000 miles on it!

     4WD Hardware has a blow-out diagram and available parts listing for the AX-15 transmission. For direct access online, click here!

AX-15-93: The must replacement items for any high mileage transmission include all bearings, synchro springs, seals, nylon parts like the shift lever bushing, synchro insert plates, the shift boot/tower seal and the synchro rings that are worn. I always replace the 1^st/2^nd rings as a matter of course on a five-speed manual transmission. There was no appreciable wear on the 3^rd/4^th and 5^th gear brass rings, and they tested to specification. This is common, and I reused these unworn synchro rings. 

             Assembly sequence is critical to the AX-15 and other modern transmissions. They have way too many interrelated parts for the installer who “doesn’t need a manual.” Unless you have thoroughly learned the procedure outlined here or within a factory workshop manual covering the AX-15, you really need to use this guide. Getting creative and cutting out steps will not work, either.

The steps I outline here are proven and the fastest way to properly rebuild the AX-15. With an AX-15 on the bench, my time to disassemble, clean, inspect and reassemble the unit is 2-3 hours—excluding the time out for getting parts, blasting corroded cases, modifying main/output shafts or taking hundreds of photographs. I know which tools to use, how air tools can save energy and time, when the hydraulic press is necessary, how to wash some parts while disassembling other subassemblies—the typical timesaving measures of any “flat-rate” professional truck mechanic. If you do enough of these units and have the right tools, you will reach such a pace. The first AX-15 rebuild will take much longer—for anyone.

              Have you cleaned all parts thoroughly? Checked for warp, wear and scorching? If you have lined up the pieces that need replacing, let’s get to work!

AX-15-94: The first step involves the hydraulic press. Use a sleeve that will just clear the input shaft. Press the bearing at its hard inner race. Do not allow the sleeve to contact the seal of the bearing! Make sure the outer race of the bearing rotates freely while installing the bearing.

AX-15-95: I hold the jack handle with a reasonable load when the bearing seats. Make certain the bearing is securely against a clean, flat bearing stop on the input shaft. There is no need for an oil slinger with this type of sealed bearing. The snap ring groove should be visible. The original ring should fit the groove, or you have not pressed the bearing fully into place. 

AX-15-96: Here, a snap ring of the same thickness as the original fits perfectly in the groove. This snap ring groove seldom changes shape. Bearings like a quality NSK, sourced through 4WD Hardware along with all of the other replacement parts for this AX-15 transmission, fit exactly and meet the original dimensions perfectly. Always buy quality bearings.

AX-15-97: The front counter gear bearing will require force to install. Note that the bearing is a three-piece arrangement. The thrust fits at the back of the bearing as shown. The insert/inner race fits inside the rollers. 

AX-15-98: I drive the bearing into place. The impact socket fits neatly over the shaft and taps against the inner bearing race. Force must be against the inner race only. Note the block of wood supporting the bottom of the counter gear/cluster. A slight amount of grease on the shaft, and the bearing moved into place with just the use of a plastic sand head hammer. More force than that, and I would be using the hydraulic press.

AX-15-99: Install the lock ring with channel locking pliers. The conventional snap ring pliers will not work well here, as the gap in the ring’s opening is too large. Make certain that the lock ring seats completely and is tightly secured in the groove. This applies to all snap rings, C-clips and E-clips. These rings must not loosen in service. 

AX-15-100: I coat the seal bore of the retainer with Super 300 sealant, a uniform film around the bore wall. Use a suitable driver or a socket that will fit safely between the inside of the seal jacket and the spring-loaded seal lip. I drive evenly with a sand head hammer, checking constantly to keep the seal square in the bore. Tap very lightly, or you may drive the seal too far! I grease and install the input shaft in the seal to confirm seal lip contact points. This is the correct seal depth, exactly where the seal ran before. 

     Caution—This seal should not be driven to the base of the retainer bore. The best criteria for setting the seal depth is by placing grease on the sealing surface of the shaft. I check alignment of the seal’s double lip by fully seating the input shaft. Check often as you drive the seal into position. 

AX-15-101:  I happen to have a driver that works well for the extension housing seal. The bore coated with Super 300, I drive the seal carefully. The goal is to seat the seal in its original location or flush with the bore’s face. (This places the top of the seal in line with the bore face.) Mating this transmission to the Atlas II transfer case input, I set the seal just slightly deeper, aligned with the lower edge of the chamfer at the outer end of the bore. Always grease the seal lip recess with quality chassis grease. This applies to the front bearing retainer seal as well.

AX-15-102:  Within the extension housing is the reverse pin. If you need to clean, service or replace the reverse pin, remove the plug at this section of the case. You can access the spring roll pin in this way. Drive the roll pin inward to release the reverse pin. (Note: On this AX-15, there is no need to service the reverse pin. I am simply demonstrating how to access the roll pin if you need to service the reverse pin.)

AX-15-103:  The reverse pin is readily accessible in the extension housing. Once the spring roll pin is driven through the shaft, you can remove the assembly. I am sharing this information to help clarify how the reverse pin comes loose. Inspect the spring tension and free movement of the reverse pin mechanism. This device is very durable, and unless damaged, it will continue to offer service for a long time. 

AX-15-104:  Here are the 1^st gear (right) and 2^nd gear (left) plus the synchronizer pieces, each in their order of assembly. The synchronizer’s outer sleeve doubles as the reverse gear. This is a busy and important assembly. Inspect the parts carefully after cleaning them. The 1^st/2^nd synchronizer assembly gets a workout on Jeep YJ and TJ Wrangler 4x4s! Note that I am installing new brass synchro rings and new insert plates and springs, each of these parts sourced from 4WD Hardware. Typical replacement parts are readily available for the AX-15.

AX-15-105:  Here, I detail how to assemble the 1^st/2^nd synchronizer. Begin by placing the sleeve in position. If you did not mark these parts for direction during disassembly, take note of the faint wear pattern on the hub’s inner thrust faces. Match the direction of installation with these patterns. For the 1^st/2^nd synchro hub, there are no other distinctions.  Install the sleeve with the offset shift lever groove facing toward the front of the transmission. Install the three inserts and one spring, exactly as shown here.

AX-15-106:  I spin the hub 180-degrees and install the second spring exactly like the first. The aim is to have the gaps in these springs facing opposite each other. (Since there are three inserts 120-degrees apart, it is impossible to have the gaps exactly 180-degrees apart.) This is the correct installation. Note how I place the spring ends just beyond the insert plates. Be sure that the plates, springs, hub and sleeve align properly. The springs will seat against the hub face when the synchro rings fit into place. 

AX-15-107:  Here, the brass synchro ring is in place. Notches align with the inserts. The synchronizer ring keeps the spring against the hub face. I oil the new brass ring’s cone-shaped braking face with 75W-140 Mopar Synthetic Gear Lube, just a film for now. If you do not oil these pieces, they could stick during initial run-in and cause balking shifts. These brass blocking or synchro rings are crucial to proper shifting. 

AX-15-108:  Note the distinction between the wear pattern on this inner hub thrust surface and the opposite side shown in the last photo. I use this as a final confirmation of the direction that this hub should face. With a new 1^st/2^nd gear synchronizer hub, match the direction with the old hub or note the inner splines’ slight recess and ramp that faces forward. (Rearward facing side of the hub has flush inner splines.) Used parts in a transmission that has not been apart before have an established wear pattern that serves as a guide for fitment. New brass rings and springs can go at either side. 1^st/2^nd synchro plates are reversible, too.

AX-15-109:  This is the 1^st/2^nd gear assembly together. Note that the 2^nd speed gear is to the left, the first gear to the right. The synchronizer sleeve has outer teeth. This is the reverse gear. A five-speed overdrive has limited space, and this is an effective way to establish a reverse gear. The synchronizer hub supports the 1^st, 2^nd and reverse gear functions. This is a considerable load and requires strong parts with close tolerances. 

AX-15-110:  This is the 3^rd-4^th gear synchronizer assembly. Distinguishing features determine its fitment and the relationship of parts. To the front, this synchronizer engages the input gear and drives power directly through the input to the main/output shaft. To the rear the sleeve engages 3^rd gear, using the cluster/counter gear as a means for reducing speed and increasing available torque. 

AX-15-111:  Look closely at the synchronizer hub. The inner hub has a chamfer that faces toward the front of the transmission. A chamfer on the outer sleeve also faces forward. There is no chamfer at the rear of the hub. Note how I inserted the plates and springs. The ends of the spring overlap two of the plates. This is the configuration for 1^st/2^nd and 3^rd/4^th gears on the AX-15 transmission. 

AX-15-112:  Here, I have pivoted the assembly exactly 180-degrees. Note that the spring appears in the same location as in the last photo. This side of the hub has no inner chamfer and faces rearward. The gap between the two spring ends is as nearly opposite as plates spaced 120-degrees apart will allow. If I pivot the hub 180-degrees to see the opposite side of the hub, the spring will once again appear in this location. This is the spring and plate arrangement—and how it should appear at opposite sides of the hub. The spring gaps face toward opposite sides of the hub.

AX-15-113:  I am holding the synchronizer assembly in place. The chamfered inner hub and outer sleeve both face forward. Brass synchro rings keep the springs and plates seated. This is not a complicated setup. If you follow the steps closely, especially the spring and plate locations, the transmission will shift properly!

AX-15-114:  Synchro assemblies properly together, the process moves along. Install the new needle bearing for 3^rd gear. This should slide onto the main/output shaft in front of the built-in machined thrust. Note that the bearing ends flush with the shoulder and fits properly on the shaft. 

AX-15-115:  Oil the bearing lightly with 75W-140 gear lube, and slide on the 3^rd speed gear with synchro ring. This should all go together easily, with no friction or resistance. Do not force any parts.

AX-15-116: I use a press to install the synchro hub and synchro assembly. I do so not only to ease installation but also to avoid jarring the synchronizer assembly. Note that I am supporting the 3^rd speed gear and its brass synchro ring to keep it in position as the hub comes down. The intent is to keep the brass ring from dislodging, which could allow the spring and plates to come loose. You can also do this by aligning the synchro ring with the plates as these parts come into contact, pressing on the hub very slowly to avoid crushing or damaging the brass rings, plates or springs. 

     Warning— Do not move the synchronizer sleeve, or the plates and springs could come apart. This applies to the assembly even after all parts are in place. Keep the sleeve centered! If you follow the approach that I illustrate in photo AX-15-116 to seat the hub on the main/output shaft, always use extreme care. Do not pinch your fingers! Make certain that the holding fixture will keep the shaft and gear assembly from shifting or coming apart under load. There is always risk when working with the forces of a hydraulic press. Move the hub slowly, watching for any irregular movement as the hub moves down the shaft and into position. Stay out of harm’s way!

AX-15-117:  Place the selective fit snap ring in the groove. It should fill the groove snugly. If there is side play in the groove, purchase a larger snap ring to fill the gap. One size does not fit all. Use the original snap ring width as a guide. Increase width from there as needed. Make sure all snap rings seat completely and securely.

AX-15-118:  Here I make a final check of clearance between the gear and the main/output shaft built-in thrust. You should be in the 0.004”-0.010” range. This reads a snug 0.008”, very acceptable for a transmission that has 200,000-plus miles on it and came from a 1990 XJ Cherokee (the same unit used in six-cylinder YJ Wranglers from late 1989 to 1995/96 and the 4.0L TJs through 1999) . The main/output thrust and gear side-wear is negligible for this kind of mileage. I did not need to replace a single gear, hub, thrust washer or shaft! You might guess by now that I like the AX-15. 

AX-15-119:  The 2^nd gear new needle bearing and all other new parts for this AX-15 were sourced through 4WD Hardware. Quality parts, I am confident of their match for OE quality. The bearings have the same manufacturers as OE pieces. Here, I slide the 2^nd gear needle bearing into place. New bearings are good insurance for a backcountry YJ or TJ Wrangler transmission. 

AX-15-120:  Second gear slides over a lightly oiled bearing. Note that the gear hub lines up flush with the end of the bearing. The bearing and gear line up with the shaft’s step shoulder for the 1^st/2^nd gear synchronizer hub.

AX-15-121:  Now I press the 1^st/2^nd gear synchronizer assembly onto the main/output shaft. Note how I once again support the lower synchronizer ring, as my press is stable and safe. If there is the slightest doubt about your safety, stay away and move the hub slowly, aligning the lower brass synchro ring with the plates as these parts come into close contact. 

AX-15-122:  Install the snap ring onto the main/output shaft. This secures the synchro hub for 1^st/2^nd gear. The fit should be snug with no side play of the selective fit snap ring. While a screwdriver might work for this ring installation, I find that channel lock pliers work better. When using a set of pliers, do not chew up the ring, shaft or any other parts! Use care, and place duct tape on the pliers’ jaws if necessary.

AX-15-123:  There is a nylon spacer that goes between the synchro hub snap ring and the 1^st gear bearing. If installed correctly as illustrated, the needle bearing will be near flush with the shoulder step of the main/output shaft. Excessive wear on the spacer will cause bearing misalignment and too much bearing end float. If that is the case, install a new spacer.

AX-15-124:  Install the lightly oiled synchro ring on the 1^st gear side of the hub. Keep the sleeve/reverse gear centered on the synchro hub. Install the 1^st speed gear and make sure it fits flush with the synchro hub’s thrust surface. There should be no resistance as the gear slides over the new, lightly oiled bearing.

AX-15-125:  Well, here it is! This is the tiny pin that flew out of the main/output shaft during the high-pressure parts wash. Fished from the floor of the washer cabinet, this pin goes in place now. The thrust washer will keep it in place. 

AX-15-126:  Slide the 1^st gear thrust into position. Note the wear pattern, and install the piece in the same direction as the original installation. Keep the thrust in position while installing the output bearing! If necessary, use petroleum jelly to “glue” the thrust washer to the 1^st gear thrust face while installing the bearing.

AX-15-127:  One way to keep the thrust washer and pin in place is to stand the assembly upright for pressing the bearing onto the output shaft. The hydraulic press makes quick work of this process. Always use a sleeve that presses only on the inner race collar of a new bearing. This will prevent stressing and damaging rollers, ball bearings, races or plastic shields. Lightly oil or grease the shaft before pressing the bearing into place.

AX-15-128:  The new bearing fully seated, you can check the side clearance of the 1^st gear. Place a blade feeler gauge in the slight gap between the thrust washer and gear. Allowable clearance is 0.003”-0.0197”. I can hardly get a 0.016” blade to fit, a healthy sign. The actual clearance is between 0.015”-0.016”, once again impressive for original parts at this mileage. 

AX-15-129:  Aside from the wear impressions, you can use the beveled internal splines as a guide. This side of the 5^th gear goes on the output shaft first. Look closely, and you will see the snap ring impression at the outer end. This will serve as a guide for a unit that is original and not previously rebuilt with questionable workmanship. Slight bevels help the splines engage.

AX-15-130:  The 5^th gear will supposedly tap into place. I find that the AX-15 spline engagements are a precise, interference fit. A press is the most sensible approach here. Lightly oil the splines and use a suitable sleeve to clear the output shaft. Seat the gear snugly against the output bearing’s inner race/collar.

AX-15-131:  The snap ring should always fit snugly in the gap of the groove. Here, the ring is accessible and a tap with the plastic hammer drives the ring onto the shaft. Check the snap ring for tightness and fit. It should be secure on the shaft and not rotate easily. With this kind of ring, I want to feel a bit of resistance when rotating the ring. Make sure it seats all the way around. 

AX-15-132:  Oil and install the new pilot roller bearing. Like all other bearings, this quality piece came from 4WD Hardware. The bearing fits the back bore of the input shaft and accepts the nose end of the main/output shaft. There is no need for thrust washers, as this rugged bearing has thrust ends and is fully self-contained—unlike free-floating needles and washers used on many transmissions. Install a new pilot bearing in the crankshaft, and if the transfer case input is stable, the shaft alignment of the input and output should remain true for a very long and productive service life! 

AX-15-133:  Place the 4^th gear brass synchro ring in position. Slide the input gear into position, making sure the lightly oiled synchro rings are in place. This is the entire input/main/output shaft assembly. Note that this entire assembly needs to go into the intermediate plate together with the aligned cluster/counter gear. Keep the synchro sleeves centered as you handle this lengthy gear assembly.

AX-15-134:  I set the intermediate plate securely in the Bench Mule fixture. Here, the cluster/counter gear rear bearing goes into the case. I tap gently at the outer race of the bearing. The snap ring came with the new bearing and matches the thickness of the snap ring on the OE bearing. Tap the bearing flush with the plate. Note that the cluster shaft surface serves as the inner bearing race. Make sure the shaft journal does not show scoring or visible wear. If in doubt, measure for out-of-round with a micrometer. 

     Caution—If you do not have a fixture like the Bench Mule, you will need to support the intermediate plate in a bench vise with protective rubber or aluminum covers over the jaws. Do not gouge or mar the aluminum. There will be a good deal of weight on the intermediate plate.

AX-15-135:  You may need assistance loading these two shafts together. They must remain aligned and uniform as you insert them in the intermediate plate. I did this by myself, finding (fortunately) that the fit is excellent. Once the cluster shaft engaged the rollers of the lightly oiled new bearing, I tilted the whole assembly upward to align the output shaft bearing with its bore in the plate. Shafts aligned, straight and level, I am able to push them into the plate far enough to support some weight.

AX-15-136:  Continue to keep the gear assemblies aligned. To “suck up” the rear bearing on the output shaft, tap gently at the intermediate plate just outboard of the output bearing. Tap while applying rearward pressure to the gear sets at the same time. The bearing will work through the plate, exposing the snap ring groove. Shafts and gear teeth should remain in alignment throughout this process. Do not force parts. This is a precise assembly, and when all is right, the parts fit.

AX-15-137:  Install the snap ring on the output shaft bearing. Make sure that both the output shaft bearing snap ring and the snap ring on the cluster/counter gear bearing are in position and seated fully.

AX-15-138:  Install the reverse idler gear by moving the lightly oiled shaft through the intermediate plate and the gear. Note the direction that the gear faces and where the shaft alignment groove sets. Do not install the gear backward! Align the shaft’s slot with the rear bearing retainer plate tab at the back face of the intermediate plate.

AX-15-139:  The rear bearing retainer plate should fit flush against the intermediate plate. The tab at the lower left engages the reverse idler shaft’s slot. Engage the plate in the slot. Use Loctite 242 on the bolt threads, and tighten the four plate bolts. Torque specification is 13 ft-lbs. (I prefer 14 ft-lbs.) Let hardware set for a few minutes after tightening and recheck torque.

AX-15-140: On the reverse shift rail, you will find a slot for one of the small interlock pins. Petroleum jelly will hold these parts in place during fit-up. This is the only way to hold several of the interlock pieces in place during assembly. Use a generous quantity; it will dissolve later in the transmission oil. Center the interlock pin.

AX-15-141: The reverse shift rail goes in the second bore from the bottom. Slide the rail through the bore. You can C-clip the rail once in position. I prefer to wait until all rails are in place. In you do not install the C-clip at this point, keep the rail’s fork against the intermediate plate. This will help prevent the interlock pin from dislodging.

AX-15-142: This is one of several ball bearings involved with the interlock system. Without petroleum jelly, this ball will simply not stay in position. I bring it into the bore below the reverse rail and insert the ball with the assistance of a screwdriver. The ball rests in the passage above the lowest rail bore. Gravity challenges this goal.

AX-15-143:  The larger interlock plug can drop through the vertical passage. With a magnet and lots of petroleum jelly, I slide the interlock plug into position above the reverse shift rail. 

AX-15-144:  There is one more small interlock pin. It fits in the 1^st/2^nd shift rail. Find the slot and insert the plug with a coating of petroleum jelly to keep it in place. Center the pin to keep it out of the way during installation of the rail. 

AX-15-145:  As you slide the 1^st/2^nd shift rail through the intermediate plate, make sure the interlock pin stays in place. Catch the lower hole of the 1^st/2^nd shift fork as the rod slides into the gear set area. When attempting to slide rods through, you will discover the value of rotating shafts and sliding them in ways that allow their deeper grooves to permit balls and interlock pins or plugs to move out of the way. Never force these parts through! There is always a “just right” position that permits fit-up. Keep track of the balls and interlock pins or plugs. Make sure they remain in position as you adjust and position rods. 

AX-15-146: Here’s one more interlock plug. Coated with petroleum jelly, the plug drops down the vertical slot. I use a pencil magnet for this purpose. The plug lodges just above the 1^st/2^nd gear shift rail. Make sure the interlock plug seats. 

AX-15-147:  Now the 3^rd/4^th shift rail slides through the intermediate plate. It picks up the upper hole in the 1^st/2^nd shift fork before reaching the 3^rd/4^th shift fork bore. Lift the 3^rd/4^th shift fork to align the rod bore. Slide the shift rail through the shift fork’s bore. Note the direction that these two shift rail levers face. In final position, their shift slots face toward the shift tower and shift lever. (Next photo shows the relationship of the two rods and the shift forks.)

AX-15-148:  Use Loctite 242 on all threaded hardware. The special setscrews for the shift forks thread into the shift rails. These two shift fork screws torque to 14 ft-lbs. Loctite will eliminate risk of this hardware loosening in service. Let setscrews set for a few minutes and recheck torque.

AX-15-149:  Each of these three rails has a C-clip lock. Make sure these locks fit securely and seat in their grooves properly. You do not want loose parts or the risk of anything coming apart in service. Take the time to secure these clips properly. 

AX-15-150:  Slide the 5^th gear rail (the lowest of the four rails) through the reverse shift fork’s lower bore and through the bottom bore in the intermediate plate. This will keep the lock ball in position below the reverse shift rail. The 5^th gear rail need only pass through the intermediate plate enough to hold the lock ball above the 5^th gear shift rail. This interlock ball serves between the 5^th gear rail and the reverse shift rail.

AX-15-151:  Move to the back of the intermediate plate. The 5^th gear thrust ring fits on the output shaft. There is a ball lock that fits in the shaft. Install the ball with petroleum jelly, and place the thrust ring with the broad surface facing rearward. When in doubt, observe the wear surfaces and match the parts up. This general rule applies to any OE transmission that has not been disassembled before.

AX-15-152:  Here is the 5^th gear synchronizer mechanism. This spring and insert plate arrangement is unusual. The two synchro springs fit on the same side of the synchro hub. Note how they overlap and tension the plates. Note, too, that the plates only fit one way.

AX-15-153:  The 180-degree turn around reveals the back view of the synchro assembly’s insert plates and sleeve. The sleeve goes on one way, the plates fit in one direction, and the two springs overlap at a plate to keep them from rotating. Note that the beveled engagement splines of the synchro sleeve are now at the opposite side, facing the brass synchro ring as shown in the last photo.

AX-15-154:  Assembled synchronizer and hub shows the plates in position and the springs overlapped at this plate. The brass synchro ring will keep the springs in position against the hub face and also lock the insert plates in position. 

AX-15-155:  This is the entire counter 5^th gear and synchronizer assembly ready for installation on the cluster/counter shaft. (The 5^th spline gear is lying in the foreground.) Lightly oil the parts and the bearing surfaces. Make sure brass ring has a light coat of oil on the contact surface with the gear hub. Oil will prevent drag upon startup of the newly rebuilt transmission.

AX-15-156:  The bearing at the counter 5^th gear is unique. No, it is not defective; the bearing actually has a split, two-piece cage. Grease the bearing with petroleum jelly or oil it with Mopar 75W-140 oil. This will prevent friction and dry startup.

AX-15-157:  5^th and counter 5^th gears are now aligned and engaged. This is the 5^th gear/overdrive system. The brass synchronizer ring is similar to the rings used at the 3^rd/4^th gear synchro assembly.

AX-15-158: At this stage, the 5^th spline gear must go in place. While it is suggested that the splined gear will tap onto the cluster/counter shaft, this may not be possible. I prefer not to exert much pressure on the counter shaft at this point, and setting the assembly in the press would be awkward if not impossible. I elect to use a deep set impact socket, an old ½- to 3/8ths inch adapter and my air driver with a blunted chisel point. This approach will ‘dance’ the splined gear onto the lightly oiled shaft splines while I hold the synchronizer brass ring in place. I am applying minimal force to the counter/cluster gear/shaft while backing the shaft up solidly at the opposite end. 

     Caution—When driving the 5^th spline gear onto the cluster shaft, make sure the opposite (front) end of the cluster gear is supported rigidly against a block of wood. You need to place the block against a solid, vertical backup. Keeping the cluster/counter shaft from moving forward will prevent damage to the rear cluster bearing. 

AX-15-159:  Unscathed, the 5^th spline gear is now in position. You can install the snap ring, which should fit snugly within the groove. Seat the ring fully and make sure it has good tension in the groove. You do not want these parts to move out of position in service. The splines make a tight fit of the 5^th spline gear to the cluster/counter shaft.

AX-15-160:  Now you can install the reverse shift head and rail. Note its relationship with the long shift rails and also the position of the shift head. With the assembly in position, install the locking ball below the rail. This ball will fit above the lowest (5^th gear) rail, interlocking between the reverse shift head’s rail and the 5^th gear rail. Use petroleum jelly to keep the ball in its bore. (The 5^th gear rail is barely through the intermediate plate at this stage, keeping an interlock ball in place at the plate.) 

AX-15-161:  Now I slide the 5^th gear shift rail through the reverse shift head bore. Note that the rail must fit with the interlock notches facing in the correct directions. The shift fork receives the rail, and the setscrew locks the rail in position. Note the chamfered edge at the setscrew thread in the rail. This faces the screw, aligning the rail’s notches properly. 

AX-15-162:  Use Loctite 242 on the screw threads, and tighten the screw securely. Always use a torque wrench for final tightening, this time the figure is 15 ft-lbs. You want these shift forks to go another 200,000 miles or more—in position! Recheck torque after hardware sets for a few minutes.

AX-15-163:  These three interlock bores reveal the notched recesses of the rails. With all synchro sleeves in neutral mode, the rails should align properly as shown. These bores each take a ball and spring, retained by the plug.

AX-15-164:  Balls go in place with petroleum jelly. All shift interlock balls are the same diameter. The only ball of a different size is the one that locks the thrust ring at the cluster/counter gear output behind the rear bearing. This ball is noticeably smaller. The lock ball springs are each the same length except the one that fits at the extension/adapter housing—a simple enough strategy.

AX-15-165:  Note that the correct length springs all fit out to the edge of the bore. The one shorter spring will not. Save it for the extension housing’s detent spring location and detent plug, as illustrated further along in this assembly process.

AX-15-166:  Use Loctite 242 on the outer plugs. They will require a Torx® bit to tighten. These plugs are each the same size and thread. Use Loctite in a manner that will secure and help seal the plug. In aluminum, Loctite 242 (medium strength blue) is appropriate. Do not use Loctite 271 (high strength red) on aluminum, as you will risk pulling threads loose upon disassembly. I use 242 throughout the AX-15 assembly. 

AX-15-167:  Final tightening is always with a torque wrench. 14 ft-lbs is the specification for these plugs. After tightening, allow them to set for a few minutes and recheck torque. A quality Torx® bit set is my recommendation if you perform this kind of work often. For work on a Jeep YJ/TJ Wrangler or XJ Cherokee, a full Torx® driver set is imperative.

AX-15-168:  Move to the reverse shift linkage. Install the E-clip at the reverse shift arm and shift arm bracket pivot. Some do this after installing the bracket; I perform this task first. Make certain that the E-clip seats securely and will stay in place! 

AX-15-169:  Mesh the reverse shift arm engagement block with the reverse idler gear groove. This block must remain in place when you install the reverse shift arm and bracket. After installing the bracket, make sure the block is still in this groove. 

AX-15-170:  Apply Loctite 242 to the bolt threads for the reverse shift arm bracket. Carefully install the bracket, keeping the shift arm engaged with the reverse idler gear. Once the assembly is in place, secure these two bolts with a torque wrench. The specification is 13 ft-lbs; I torque to 14 ft-lbs and recheck torque after several minutes. 

AX-15-171:  This is the final view of the shift rails at the rear of the intermediate plate. Note the relationship of the shift rail levers, with a pocket among them to receive the shift arm. Look over your handiwork and make sure your transmission shows these components in place.

AX-15-172:  Here is the shift rail and gear set view forward of the intermediate plate. Make certain your transmission assembly has each of these pieces in place and sequence. Note shift linkage for the reverse idler gear and the shift forks. Use this photo as a reference.

AX-15-173:  The full driver’s side (left hand drive models) view of the assembled gears should look like this. On a transmission this busy, sequence of assembly is essential. You simply cannot leave out or skip steps. Note the reverse idler gear and the block riding in the reverse idler gear groove. Use this illustration as a reference.

AX-15-174:  Now I take the intermediate plate loose from the Bench Mule. If you were using a bench vise with cushioned jaws, remove the complete gear and plate assembly now. Tilt the unit to make the front side of the intermediate plate accessible. Support the rear of the assembly safely to prevent damage or dislodging any parts.

AX-15-175:  Clean and dry the intermediate plate faces and main case face. Make sure there is no oil or residue on the mating surfaces and that the two dowels are in place and in good condition. Apply a bead of appropriate sealant to the clean and dry intermediate plate surface or the face of the main case. A 1/8-inch bead will suffice; it will spread when the plate and case contact each other. Sealant winds inboard of the bolt holes for maximum sealing. You do not want leaks! 

     Note—The original factory recommended sealant was Mopar Gasket Maker, which is an anaerobic type sealant. Another factory recommendation has been Threebond® Liquid Gasket. Check with your local Jeep dealership to see what is currently recommended and used by the service department. I used a specified alternative here. Historically, Permatex’s 518 Gasket Eliminator has worked well on aluminum transmission and transfer case housings where there is no gasket and an interference-type, machined fit.

AX-15-176: As busy as this assembly appears, if all of the rails, shafts and bearings are in alignment, the front case will drop into position. Never force parts! Guide the case onto the rails and front bearings, constantly watching the mating surfaces. Do not dislodge sealant prior to the case mating surface coming into contact with the intermediate plate. Watch the dowels to assure alignment. 

AX-15-177:  The front bearings will require coaxing of the case with a sand filled plastic hammer. Light taps around the outside of the bearing bores will “suck” the bearings into position as the case drops into place. This should do the trick. If not, something is binding or out of alignment. The assembly is so precisely fit that cases come apart and assemble readily.

AX-15-178: Snap rings now go at the front bearing grooves. Make sure that they seat properly and fit snugly. Note the ghost line of original sealant at the case face. I cleaned this case with a glass bead blaster, lightly, and this sealant trace did not lift. It is not advisable to scrape aluminum, and the sealant trace is so thin that it will not interfere with either parts alignment or face-to-face fitment. I chose to leave it alone.

AX-15-179:  Here is the sealant bead on the surface of the front bearing retainer. Make sure the seal is in place! A 1/8^th inch bead of sealant will do here. Note that I line sealant inboard of bolt holes to assure a proper seal. Sealant will squeeze outward in both directions.

AX-15-180:  I carefully set the retainer onto the case, protecting the seal. The seal lip recess has grease filling the groove. Align the retainer and set it directly to the bolt holes. Use Loctite 242 on the bolt threads to secure and seal the front retainer bolts.

Note: Advance Adapters can supply this iron retainer to convert from an earlier YJ or XJ hydraulic style throwout bearing to the later release arm with external slave cylinder approach.

AX-15-181:  Tighten the bolts in cross until the retainer is flush. Then go around the circumference with a torque wrench a few times. Specification calls for 12 ft-lbs. I tighten this iron retainer to 14 ft-lbs on the final pass and recheck at 14 ft-lbs after a few minutes. This retainer supports the front transmission bearings and also the clutch release bearing. Fitting flush, squarely and snugly is essential.

AX-15-182:  Repeat the sealant application at the rear extension/adapter housing. A 1/8^th inch bead will suffice. More is a waste and will only make a mess as it squeezes out in all directions. Make sure the extension seal is in place with grease filling the lip recess.

AX-15-183:  Be certain the two dowels are in place and in good condition. Dowels aligned with case holes, the extension housing should tap into place without great effort. Beating is not necessary and would indicate parts misalignment. I tap lightly in a rhythmic, circular pattern around the outer face of the housing. Keep parts straight and watch the mating surfaces come together.

AX-15-184: I install the backup light switch—with a film of sealant on the threads and a new OE-type gasket—before installing the bolt that holds the wire clamp in place at the extension housing. Note that I support the transmission at the intermediate plate to keep pressure off the installed extension housing. In one factory level book, specifications call for 27 ft-lbs torque at the switch, another factory reference calls for 32.5 ft-lbs. I use an open end wrench to tighten the switch securely—to the 30 ft-lb range. If you are not familiar with torque feel, a crow’s foot (open ended wrench-socket) would work with a torque wrench. 30 ft-lbs is plenty. These threads are aluminum.

AX-15-185:  The backup light switch secure, I install the extension/adapter housing bolts. There is a recommendation for sealant on these threads. Instead, I use a uniform coating of Loctite 242 on the bolt threads to make sure they stay put and seal. Size bolts carefully, matching the stick-out lengths to determine where they fit. Tighten in cross, making sure that the extension housing remains square with the main case as you tighten the bolts. 

     Note—When using Loctite 242 as a sealant/thread locker, I take two matching bolts and place Loctite on one’s threads. With the thread ends facing toward each other and parallel, I bring the threads together, side-by-side, and swirl the two thread sets against each other. This places an even, more uniform coating on the threads, highly effective and not wasteful. Try it!

AX-15-186:  Tighten to final torque with a torque wrench. The bolt torque specification is 27 ft-lbs for extension/adapter housing bolts. Tighten in cross then go around the 10-bolt pattern. Let parts set several minutes and recheck the torque.

AX-15-187:  Install the reverse shift rail detent ball and spring. The ball is common detent size; however, the spring is the short spring (at right) in the set. 

AX-15-188:  Note that the spring fits to the end of the bore. Use Loctite 242 on the detent plug threads to secure and seal the plug. Install the plug and torque to 14 ft-lbs. After several minutes, recheck torque.

AX-15-189:  Drop the last interlock ball into the top opening in the intermediate plate. The spring is the same length as the three interlock/detent ball springs that fit the side of the plate. 

AX-15-190:  Use Loctite 242 to seal threads and secure the access plug. Tighten the plug to 14 ft-lbs with a Torx® bit. Recheck after several minutes. This is the last ball, spring and plug. 

AX-15-191:  Insert the shift arm shaft, its oil passage bore facing to the rear. The threaded setscrew section of the shaft has a chamfer at one end. I install the shaft with the chamfered end of the threads facing upward. The shaft’s side oil hole will aim correctly. Here, the shaft fits through the shift arm’s bore. I will rotate the shaft to align the chamfered end of the threads with the setscrew hole in the shift arm. 

AX-15-192:  Engage the shift arm with the shift rail levers. Recall, there are three shift lever ends that form a pocket. The shift arm rotates and moves within the three levers. You can feel the arm engage the space among the levers. When aligned and centered correctly, the shift arm pedestal and the shift lever bore will face straight up. Adjust the shift arm shaft to align the chamfered end of the threads with the shift arm’s setscrew hole.

AX-15-193:  Install the setscrew with Loctite 242 on the threads. This screw torques to 28 ft-lbs. Tighten securely with a torque wrench, let the screw set for several minutes, then recheck torque. 

AX-15-194:  I coat the restrictor pin threads with a bead of sealant/adhesive—not Loctite. (Loctite on aluminum threads of this size could create a problem when removing these pins later.) An appropriate sealant with adhesive properties will seal well and form an adhesive bond as security.

AX-15-195:  Tighten restrictor pins to the minimum specified 14 ft-lbs. Here, I bring restrictor pins to near specification with a box-ended wrench. I will use a socket and torque wrench to verify final torque. Recheck torque with the torque wrench after pins have set for several minutes. I re-torque to 15 ft-lbs. 

AX-15-196:  Coat the shift arm shaft plug’s threads with a film of Loctite 242. This will serve as a sealer and secure the plug well. The plug faces the cavity of the adapter, and a leak here would allow oil to seep out of the adapter/extension housing bleed hole.

AX-15-197:  Torque the shift arm shaft access plug to 14 ft-lbs with a torque wrench. Recheck torque after several minutes. By now, you know that I recheck torque. Hardware seats and settles. Some mechanisms generate friction during tightening. A recheck of torque means this unit is secure and ready for a long service life.

AX-15-198:  Coat each side of a new shift tower gasket with Super 300 sealant. (I sourced the gasket through 4WD Hardware with the other parts.) Place these pieces carefully atop the adapter/extension housing.

AX-15-199:  I use Loctite 242 on bolt threads and run the bolts down quickly with a speed handle. Tighten in cross and evenly. Secure to a final torque setting of 14 ft-lbs. Let hardware and the gasket set for several minutes then recheck torque.

AX-15-200:  The shift lever and mechanism can be cleaned thoroughly and painted. The lever had rust that cleaned up nicely on the wire wheel. I installed a new plastic end bushing, sourced from 4WD Hardware, at the lever mechanism. The gloss black paint is rust resistant, a good idea for a Jeep 4x4!

AX-15-201:  Grease the shift lever bore with light chassis grease. The nylon seat bushing will benefit from grease. I also greased the new nylon bushing that engages the shift arm.

AX-15-202: Install the shift lever spring. I coat this part with grease to prevent rust and friction. The spring fits this way.

AX-15-203:  This retainer has slots on each side that engage the locating pins in the shift tower. Spring loaded, you can press down on the retainer, compress the spring then turn the retainer clockwise until the lugs engage. Release the retainer, and the spring will hold the pieces in place.

AX-15-204:  This is the position of the retainer when seated. Here, I have applied pure silicone spray to the shift boot center and very carefully slide it over the square end of the short lever. The new boot and gear shift knob were sourced from 4WD Hardware with the other parts; the boot will keep dirt and debris out of the freshly rebuilt transmission. 

AX-15-205:  Boot seated and secure, you can also see the new shift knob here. Fortunately, these parts are readily available to Jeep owners. If you find that parts are not available as OEM Authentic Mopar pieces, 4WD Hardware provides high quality replacement parts, including this knob. I found that these parts all met OEM standards.

AX-15-206:  The new front bearing retainer was unpainted. I use this rust-inhibiting paint to seal and prevent rust at the new retainer. This retainer will enable use of the external slave cylinder clutch housing and clutch linkage. In the engine installation chapter, I detail how these upgrade pieces fit together. The original internal slave cylinder/release bearing uses a bearing retainer without the release bearing extension. 1993-up YJs and all TJ Wranglers use the external slave cylinder with the AX-15.

AX-15-207:  Well, here is a like-new Aisin AX-15, ready to deliver years of trouble free service—like your buildup should! Here is the right side of the unit. I ran the shift lever through each gear position, rotating the input shaft and feeling output speeds at the output shaft. This transmission shifts beautifully!

AX-15-208:  Here is the left side of the freshly rebuilt AX-15. The shift lever extension and new motor mount will install with the transmission. In the engine chapter, you will find these details and the clutch installation as well. The AX-15 is a worthy, rugged light-duty truck transmission that will readily handle the high output 4.0L inline six-cylinder power. In rebuilt or good condition, this transmission should handle 250-275 horsepower under reasonable 4WD use.

AX-15-209:  My last step is to measure the stick-out length of the output shaft. Stick-out is the amount that the shaft end extends beyond the face of the adapter/extension housing. This measurement is 0.350” after my removal of material to accommodate the mate-up to an Advance Adapters Atlas II transfer case. The stock stick-out length will, of course, be longer. 

Well, that is the complete rebuild of an Aisin AX-15 transmission! I am impressed with the design and integrity of this gearbox. Quality new parts from 4WD Hardware or Mopar/Jeep can restore the stamina and reliability of such a 200,000-plus mile transmission. I would readily trust an AX-15 behind horsepower in the 250-275 range—when driven sensibly. If you want to raise the horsepower beyond this level, consider an NV4500 conversion. (See Advance Adapters for details.)

     Caution—Remember, in any five-speed overdrive transmission, 5^th gear on the main-output shaft faces the greatest load— yet this is the smallest gear of the forward speeds. Use 5^th gear prudently, and avoid overloading or taxing the 5^th gear!  

     Additional articles at this website will cover details on the installation of a new clutch assembly, clutch linkage and mate-up of the manual transmission to the engine—essentially the reverse of the transmission removal steps. I also detail crankshaft pilot bearing replacement, the clutch linkage upgrade to 1993-up design (external slave cylinder), clutch upgrade options to match a high output 4.0L or "stroker" six-cylinder engine’s horsepower, and how to service and safely install the flywheel. For now, we have rebuilt the Jeep/Aisin AX-15 five-speed manual transmission to professional, "factory" standards!

Copyright 2010 © Moses Ludel...Enjoy this comprehensive, color-illustrated article and photography by Moses Ludel. The article is available solely at the 4WD Mechanix Magazine website and can be viewed here as often as you like. If you wish to share the article with friends or professional colleagues, please refer them to 4WD Mechanix Magazine website: www.4WDmechanix.com. As copyrighted material, this article and the photography cannot be copied or distributed in any other form.—Moses Ludel