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How-to: Rebuilding a Jeep AX15 Transmission—Disassembly & Inspection

Jeep AX-15 transmission apart and ready for assembly.

     For the first-time rebuilder of an AX15 transmission, I recommend that you follow my step-by-step procedures outlined in this two-part article. There are no shortcuts. Steps must be followed carefully when disassembling or reassembling an AX15. Otherwise, you risk the chance of damaging expensive parts or winding up with an unreliable transmission.

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

     Caution: When purchasing synchronizer parts, make sure you match the 3rd/4th gear synchronizer pieces. Aisin changed the bronze ring and sleeve design in the late 1990s. Aftermarket rebuild kits may contain the earlier parts, which do not match the late synchronizer pieces and will cause problems. See the forum posts for more details—links available in the "Note" below...

  Note: You can gain a valuable understanding of the AX15's functions by watching this "third-party" YouTube video embedded at the forum posts on AX15 rebuilding issues. The presenter does an excellent job of describing the functions of this transmission. You will find this video helpful. View it as you diagnosis and follow my rebuild steps in this 2-part article! You also want to check out the synchromesh parts design issue for the 3rd/4th synchronizer assembly on the late AX15 Jeep transmissions. There is an excellent discussion at the forums regarding "earlier" versus "late" 3rd/4th gear synchro parts and a number of other AX15 issues, click here!Moses Ludel 

     I enjoy rebuilding the AX-15 transmissions. A more sophisticated unit than most domestic (U.S. design) Jeep gearboxes, the AX-15 borrows architecture from European and Asian transmission designs. Fitting parts precisely, taking careful measurements of the tolerances, and deciding whether to reuse or replace various parts are just some of the reasons why the AX-15 is a much busier, yet gratifying, transmission to rebuild. Look over my closely staged and illustrated steps and decide whether this is the kind of project that you want to tackle!

  There are two parts to the Aisin AX15 transmission rebuild. Follow Part 1 (below), then click here for "Rebuilding the Jeep AX-15 Transmission, Part 2". Get close-up details on assembling the AX15 to function as new!

     Note: Due to popularity and reasonable parts sources, the Jeep Aisin AX-5 and Jeep AX-15 transmissions remain serviceable. Jeep dealerships, 4WD transmission shops and Jeep owners rebuild these transmissions. Jeep dealers and the aftermarket can provide service parts. Having rebuilt light-, medium- and heavy-duty truck transmissions for more than four decades, I view the AX-series units as “busy” designs from a service standpoint. If, after carefully considering my 'how-to' steps and photos, you decide not to rebuild your original transmission, consider a replacement or a factory-remanufactured unit from sources like Mopar or Advance Adapters. This article and my accompanying studio-level photography will serve owners of the Jeep XJ Cherokee, Jeep YJ Wrangler and Jeep TJ Wrangler.

Moses Ludel    

Beginning the rebuild of Jeep AX-15 transmission.

AX-15-1: Here we go! This is the core AX-15 unit that will serve as our prototype for a rebuild. The destination for this 1990-circa, high mileage unit is an ’87 YJ Wrangler. An Advance Adapters’ Atlas II transfer case will mate to this renewed transmission. The engine will be a Mopar Remanufactured 4.0L long-block with the Mopar EFI/MPI conversion package. Good for 170-190 horsepower in this chassis, the engine demands a durable, rugged transmission. Let’s build one! 

Early style Jeep AX-15 has a hydraulic clutch release bearing.

AX-15-2:  The front view reveals the vintage of this AX-15. Note that in 1990, actually up through 1992, the AX-15 uses an internal slave cylinder/release bearing. The front retainer has no provision for a conventional release bearing. In the build-up, I will install a new, iron retainer that works with the 1993-up external slave cylinder, clutch housing and mechanical release arm mechanism. This is a simple, purposeful changeover.

Jeep AX-15 transmission with 23-spline output shaft. 

AX-15-3:  The rear view of this AX-15 shows the characteristic 23-spline output shaft. On the YJ and TJ Wrangler AX-15 applications, the output shaft extends nearly ½” beyond the rear face of the transmission extension housing. The NV3550 is typically an output shaft that ends flush with the rear face. The AX-15 must mate to the correct transfer case input gear. For an Advance Adapters’ Atlas II transfer case conversion, the output shaft of this AX-15 will require slight shortening. (See this step in the rebuild details.) 

Shift tower of an AX-15 Jeep transmission.

AX-15-4:  This is the shift tower. On AX-5 and AX-15 units, you can reach above the tower when the transmission is in the chassis, raise the shift boot, press down on the spring-loaded retainer, and rotate the retainer counter-clockwise to release it from the two pins in the tower. The shift lever lifts out readily once the spring-loaded retainer is loose. Inspect these parts for wear. Replace the old bushing at the lower tip of the level. This bushing wears or becomes brittle with age. 

Rebuild of AX-15 Jeep transmission requires metric tools.

AX-15-5:  Now, the rebuild begins. Follow my steps closely for quick, safe disassembly. Start with loosening the shift arm retainer bolt. Hardware is all metric on these transmissions.

Removal of restrictor pins on Jeep AX-15 transmission.

AX-15-6: Remove the two restrictor pins. These pins come loose readily. They have a spring-loaded ball bearing at the inner end and play an important role in limiting and tensioning the shift lever movement. This is where shift “feel” begins.

Removal of AX-15 Jeep transmission shift lever shaft plug.

AX-15-7:  At the front of the transmission case, loosen the shift lever shaft plug. This hex insert is 10mm metric. Use the correct tools to prevent damaging hardware. A stripped insert hex plug is extremely difficult to remove. Replacement parts may not be easy to find. The right tool will protect your transmission and ease the task. 

Jeep AX-15 shift lever shaft removal with a magnet.

AX-15-8:  The shift lever shaft is generally easy to remove. A shop pick-up magnet works well for catching the end of the shaft and sliding it out. The shaft should move freely. Do not force precision-fit parts. Note the oil hole in the shaft’s outer end.

AX-15 Jeep transmission shift lever shaft inspection.

AX-15-9:  Now the shift lever shaft and shift lever arm are free. Inspect the contact surfaces for wear and damage. This is a durable setup. The transmission has well over 200,000 miles on it, and this is the original shaft and arm—still reusable.

AX transmission detent ball removal on Jeep AX-15.

AX-15-10: The Aisin AX transmissions use several detent plugs with springs and balls. Interlock plugs and balls regulate shifts and prevent grabbing two gears at one time—a good idea! During disassembly, you will need to account for the access plugs, springs and the interlock plugs, pins and balls. Removing these pieces in sequence will prevent damage and permit shafts to move readily out of position. Here, I remove this plug with spring and ball.

Removal of backup light switch from AX-15 Jeep transmission.

AX-15-11:  I removed the extension housing/case bolt that secured the wire bracket for the backup light switch. The backup light switch is now ready for removal. Use the correct wrench, and protect the wire during removal. This switch still works after 20 years of service! Good stuff. 

Jeep AX-15 extension housing bolt removal.

AX-15-12:  Now, you can remove the rest of the extension housing bolts. Carefully circle the housing to make certain that you have located each of the 10 bolts. Never force parts. If you remove all of the extension housing fasteners, the case will separate properly. Note the length of the bolts and where they were fitted.

Jeep AX-15 extension housing removal.

AX-15-13:  You should now be able to tap the extension housing rearward. This unit had sealant/adhesive on the mating surfaces, and breaking the seal required carefully tapping at the flanges. Rearward of the hammer, there are small triangular tabs designed for tapping—gently. That was not working according to plan, so I tap at the heavier extension/adapter flange to avoid damaging or breaking the wing tabs. Do not use excessive force—this is aluminum!

Jeep AX-15 extension housing slides rearward.

AX-15-14:  Once the seal has broken, the extension housing should slide rearward. Keep the housing level, and slide it loose carefully. Do not force any pieces and avoid binding the parts. This is a precisely machined assembly and should be handled properly. Aluminum scratches readily, gouges and can even break if mishandled. Tough material when installed properly, these housings hold up very well over time. 

Removal of Jeep AX-15 extension housing seal.

AX-15-15: Extension housing free of the intermediate plate, you can place the housing on the bench. Place the housing with the seal and rear face upward. Pry or drive the old seal out. If you use a pry tool, do not gouge or scratch the aluminum! The seal will come loose readily. At this stage, inspect the reverse pin assembly closely.

Jeep AX-15 front retainer plate removal.

AX-15-16:  All retainer bolts removed, gently pry the front retainer plate away. Always brace against a surface that will not become damaged. Again, this is aluminum, so use extra caution. Force needed should be minimal.

Driving out front retainer seal from Jeep AX-15 transmission.

AX-15-17:   Drive the seal out of the retainer. A socket and plastic sand head hammer is a good tool for this task. The seal will come loose readily. Japanese and European seals have a different style jacket. Seals install and come out easily, stay put and seal well for a long time. 

Front bearing and snap ring on Jeep AX-15 transmission.

AX-15-18:  With the retainer out of the way, the front bearing and its snap ring are visible. I use a bill-type snap ring pliers to spread the snap ring. Spread rings evenly. Minimize distortion by only opening the ring enough to clear the groove. The Aisin transmissions use selective fit snap rings in several locations to align parts, set end float or establish gaps and clearances on precision fit pieces. Always identify and match up the location of these rings. Measure their thickness with a micrometer or accurate dial caliper.

Front counter gear snap ring on Jeep AX-15 transmission.

AX-15-19: Remove the front counter gear snap ring. The procedure is the same for this flat snap ring. Ends are easy to grasp with this type of snap ring pliers. Buy a good pair—this heavy duty New Britain set is 33 years old now and still working. I like the design for transmission work. Today, Stanley Proto makes a quality replacement pliers:  Click here for a link to Stanley's website tool listings.

Tap at flange tabs to prevent damage on Jeep AX-15 transmission.

AX-15-20: Tap at the flange tabs and carefully break the sealant seal at the intermediate plate. You want this intermediate plate to separate smoothly and straightly. Do not bind up the parts during this important step. Even after years in service, this AX-15 comes apart without a fuss.

Use of Bench Mule for Jeep AX-15 transmission work.

AX-15-21:  Note how I am supporting this transmission from the front face, using the Mark Williams Enterprises ‘Bench Mule’ as a stand. The entire gear assembly will move outward with the intermediate plate. I support the plate and gearset to keep the assembly level. Tapping lightly at the input nose and the counter gear with a plastic hammer, I make sure the assembly slides rearward, with the input and main/output shaft gear sets plus the counter gear all moving together. 

     Note—If you do not have a fixture like the Bench Mule, you will need to support the transmission in another way. The typical method for supporting the intermediate plate is a bench vise with protective rubber or aluminum covers over the jaws. Do not gouge or mar the aluminum. There is a good deal of weight on the intermediate plate.

Gear assembly removal from AX-15 Jeep transmission case.

AX-15-22: When the input shaft bearing and countershaft bearing clear the front face of the transmission, the entire gear assembly can be safely removed. Do not drag parts against delicate aluminum bores or casings. Keep the gearsets together and aligned. Lift the gear sets free. Be cautious, this is an awkward assembly to handle. (Glad I have a Bench Mule! This stand is more than a decade old and still highly functional, a great shop asset, especially if you work alone.) 

Relationship of gears and shaft in a Jeep AX-15 transmission.

AX-15-23:   Gears and shafts in alignment, you can see the relationship of the counter gear to the input/main shaft gear sets. Note that the entire gear train is still intact. Despite complexity of this assembly, the whole unit came free from the front case without difficulty—once I removed the appropriate parts.

Profile of gear assembly on AX-15 Jeep transmission.

AX-15-24:  This is a busy transmission! Note the shift rails, forks, gear sets, intermediate plate and small parts. On the edge of the intermediate plate, the plugs align for the shift rail balls, springs and interlock plugs and pins. Plugs make access and service quick and practical.

Use of Torx® sockets on AX-15 Jeep transmission work.

AX-15-25:  Plugs removed with a Torx® bit socket, you can now use a magnet to access and extract the springs, balls and interlock plugs. Again, proper tools are necessary for removing parts. While not expensive, tools like the Torx® bits and metric Allen sockets make this work easier and prevent damage to the transmission parts.

Removal of snap ring from AX-15 Jeep transmission.

AX-15-26:  Two screwdrivers placed evenly at the snap ring will enable a light hammer blow to drive the snap ring loose. Although I am using a blade and Phillips screwdriver here, the better approach is a pair of matching blade screwdrivers. Use a plastic head hammer to prevent tool damage. Expect the tensioned ring to come off with force.

Pry snap ring carefully from AX-15 Jeep transmission shaft.

AX-15-27:  When possible, move the snap ring this far out of the groove. Now you can place a blade screwdriver in the gap. Twist or pry the snap ring loose. Again, avoid damaging snap rings, as they must be intact for measuring thickness. These are selective fit and cannot be mixed. Note the location and thickness of the ring.

Reverse arm shift bracket removal AX-15 Jeep transmission.

AX-15-28: Two bolts hold the reverse shift arm bracket to the intermediate plate. You can loosen the shift arm’s E-clip retainer first, whichever is easiest. Here, I loosened the bracket before removing the E-clip.

E-clip removal from AX-15 Jeep transmission reverse shift arm bracket.

AX-15-29:   Now you can see the E-clip. Pry it loose with a screwdriver in one of the slots, and you can then detach the shift arm from the shoe. The shoe rides on the shift rail. 

Reverse shift arm free during AX-15 Jeep transmission rebuild.

AX-15-30:   Shift arm is now free. The shoe hangs loose from the rail. Once again, these parts must come loose in sequence, and these steps precede the next series of tasks. Follow the sequence to correctly tear down and assemble this unit. 

Jeep AX-15 5th gear fork setscrew removal.

AX-15-31:   Remove the 5th gear fork setscrew. Note that this is a metric socket. Follow the sequence, using the correct tools for each task. 

Jeep AX-15 5th gear shift fork removal.

AX-15-32:  Slide and remove the 5th gear shift fork. Do not force parts. You may need to slide parts out of the way. The fork should come loose without much effort.

Jeep AX-15 reverse shift head and rail removal.

AX-15-33:  Remove the reverse shift head and rail. This comes out as an assembly. There is no need to disassemble the shift head from the rail. 

Jeep AX-15 transmission 5th spline gear removal with puller.

AX-15-34: Here, I am placing the jaws of a two-jaw puller behind the 5th spline gear. (The gear also has two bolt holes at its face for use of a slotted rail or damper type puller.) This gear takes force to remove. If you use a hand wrench or socket and ratchet to rotate the puller stem, keep the puller’s jaws from rotating to prevent damaging other parts. I choose to lubricate the puller’s stem with hi-temp grease to prevent friction damage and carefully rotate the stem with a deep-set impact socket and my air gun set at light pressure. Wear goggles when applying impact force.

Jeep AX-15 counter 5th gear and synchronizer assembly removed.

AX-15-35:  The complete counter 5th gear and synchronizer assembly is now free of the countershaft. The gear and splined piece are not damaged and neither is this caged needled roller. Despite the ominous appearance of a “broken” bearing cage, this is actually a two-piece caged needle roller assembly. Always protect parts during disassembly. A few minutes of care may save a good deal of expense. These are precision parts. 

5th gear assembly removed from AX-15 Jeep transmission.

AX-15-36: This is the 5th gear assembly. There is a synchronizer on 5th gear and a rugged pair of gears for a light-duty truck transmission. 5th gear on the main/output shaft is much smaller and the most vulnerable gear in any overdrive transmission. However, the AX-15 has considerable stamina and gear integrity. These gears hold up very well. This 200,000-plus mile unit is a living testimonial. I am very impressed with how these designs have evolved. The AX-15 is way more durable than the T-5 overdrive transmissions found in 1980s Jeep CJ models! 

Jeep AX-15 5th gear thrust and lock ball.

AX-15-37: Behind the 5th gear you will find the 5th gear thrust and its lock ball. The thrust is extremely good material and built to last. The 5th gear on the main/output shaft is visible above the thrust and counter gear. Note the width and material of these gears. Although not comparable to an NV4500 one-ton truck design, for a lightweight XJ Cherokee, YJ Wrangler or TJ Wrangler, the AX-15 is quite impressive! I’d readily put 250-275 horsepower in front of this unit—once the rebuild restores the transmission to top condition.

Removal of rear retainer plate on Jeep AX-15 transmission.

AX-15-38:  Remove the bolts attaching the rear retainer plate to the intermediate plate. This steel plate will readily come loose once the four bolts are removed. Use the flat edge of a pry tool to gently lift the plate free.

Reverse idler shaft removal from AX-15 Jeep transmission.

AX-15-39:  The retainer plate holds the reverse idler shaft in place. With the retainer plate removed, you can slide the reverse idler shaft loose and free the reverse idler/sliding gear. I inspect the reverse sliding gear inner bushing for both wear and the degree of wobble between the reverse idler shaft and the bushing. 

Removal of 5th gear shift rail from AX-15 Jeep transmission.

AX-15-40:  When removing the shift rails, rotate them to free up pins, balls and interlocks. Here, I rotate and remove the 5th gear shift rail. Note that all ball, plug and pin pieces must be removed. Place them in a safe location. If in good condition, they can be reused. Do not force rails out. If they are not moving, there is an obstruction. Rotate and gently slide shafts to free interlock pins, plugs and balls.

Shift fork set screw removal from AX-15 Jeep transmission.

AX-15-41:  Remove the shift fork setscrews. Set the screws aside safely. This is all unique hardware and high grade steel. Finding replacement parts can be difficult and costly. Reusable parts must be preserved and not lost. 

Two scewdrivers remove C-clips on AX-15 Jeep transmission shift rails.

AX-15-42a:  Here, I am once again using the two-screwdriver technique to loosen the C-clips on the shift rails. This is the professional method for driving the clips loose. Apply uniform pressure to each end of the ring. Beware: These clips will fly off the bench if you do not catch them! Drive the clips away from your face and eyes. (Eye protection is always a good idea.) A light, controlled tap with the plastic hammer head will do the job. 

Last C-clip removed from Jeep AX-15 transmission shift rails.

AX-15-42b: This is the last of the three C-clips. I can generally push these loose by hand, without the need for a hammer. Press evenly at each end of the clip. Use flat blade screwdrivers.

Rotate to remove 1st/2nd gear shift rail from Jeep AX-15 transmission.

AX-15-43: Rotate and remove the 1st/2nd gear shift rail. Watch for interlock pins and small parts at the plug holes. Find the position of the rail that will free up the locks and allow the shaft to slide out freely. Never force these rails loose! Reassembly of parts is in careful sequence as outlined in Part 2 of this article. 

Keep track of small parts when rebuilding the Jeep AX-15 transmission.

AX-15-44: Keep track of small parts: plugs, interlock pins, balls and springs. These pieces are critical to keeping your transmission in gear. You must keep these pieces in a safe place after cleaning them. It is amazing how much delay can be created by misplacing or losing one of these small parts—then trying to find its replacement.

     Note—I place small parts in a special metal basket for cleaning in my parts washing cabinet. When I sent the AX-15 pins and small parts on a wash cycle, two small pins managed to find their way through the tiny holes in the basket. (45 PSI nozzles and pressure spray had a lot to do with this!) Once the machine cooled down, I spent 30 minutes with a magnet and long-sleeved glove, combing the washer floor by hand. Fortunately, I found both pieces. Tiny parts can be washed separately with a small pail, solvent and a parts cleaning brush!

3rd/4th shift rail removal from Jeep AX-15 transmission.

AX-15-45:  The 3rd/4th shift rail can now slide free. Rotate the rod to free up the small parts and find the point where the notches and parts become free. If the rail will not slide, something is in the way. Carefully catch forks and set them aside. 

Magnet gets workout when rebuilding an AX-15 Jeep transmission.

AX-15-46: Remove the locks, springs, pins and balls with a magnet. This mechanic’s pickup magnet has served me for over 35 years! It still functions well and fits neatly into the bores of transmission shift mechanisms. For transmission and transfer case work, you need a magnet like this one.

Use the right Torx® bits to prevent damage to AX-15 Jeep transmission parts.

AX-15-47:  Again, the Torx® bit socket fits snugly into a plug head. This head atop the intermediate plate will access the bore to the lower rail. If all of these springs, balls, pins and interlock plugs are difficult to track, do not be concerned. I will show how and where to assemble each of them—in proper sequence—during the assembly phase of this rebuild. 

Removing spring and barrel-shared interlock plug from AX-15 Jeep transmission.

AX-15-48:  Plug removed, the spring and barrel-shaped interlock plug come out. The magnet helps once more, removing parts deeper in the plate’s bore.

Reverse shift rail and fork slide out from Jeep AX-15 transmission.

AX-15-49:  Now the reverse shift rail and fork slide out. Rotate the fork to ease removal. There should be no obstructions. To be safe, check the bores for any small parts and lift them out with the magnet if necessary. Account for all pieces.

Profile of gear sets in a Jeep AX-15 transmission.

AX-15-50: Now you can see the gear sets! This is a nice setup and very well constructed. Although busier in a service sense, built properly, the AX-15 makes a very reliable and rugged transmission.

     Note the power flow and gear sizes. This is a “close-ratio” five-speed with nice, uniform spacing of the gear ratios: 1st-3.83:1; 2nd-2.33:1; 3rd-1.44:1; 4th-1.00:1; 5th-0.79:1 and reverse 4.22:1. With lower (numerically higher) ratio gearing at the axles and transfer case low range, the AX-15 is highly functional.

Removal of output bearing snap ring on AX-15 Jeep transmission.

AX-15-51: Remove the snap ring at the output bearing. Use a quality snap ring pliers. These revered pliers have been ground for special application use, and I’m due for a new set soon. (This pair will still serve for special uses.) Look for a set like this duck-billed steel type, a quality set could last for 35 years or more.

Counter gear rear bearing snap ring removal from AX-15 Jeep transmission.

AX-15-52:  Similar to the front of the transmission, the counter gear rear bearing snap ring is next in sequence. Snap rings secure bearings and precisely align the gears, bearings and thrust washers. Keep track of these selective fit snap rings and their positions. Lay out the disassembled parts in order. If necessary, make notes on duct or masking tape indicating the location where the snap ring fits. Tape notes to each snap ring.

Tapping counter shaft and main-output shaft ends of AX-15 Jeep transmission.

AX-15-53:  Tap the counter shaft and main/output shaft ends. Tap evenly, a light tap at each shaft to keep the parts moving out together. You want the gear sets to each drive through at the same time. Keep shafts and gear sets aligned.

Support shafts to prevent binding when working on AX-15 Jeep transmission.

AX-15-54:  Support shafts and prevent binding or jamming of parts. Do not allow synchronizers or gear components to knock against each other. Take your time here.

Use plastic head hammer when working on Jeep AX-15 transmission.

AX-15-55:  If necessary, tap the counter gear end with a plastic head hammer. This Stanley hammer has a sand filled head and packs a great wallop when necessary. At the same time, it can deliver a modest, controlled and deliberate kind of force capable of sliding parts like this shaft. The bearing stays in the plate as the shaft slides free. There should be no resistance between the bearing and shaft.

Empty plate during Jeep AX-15 transmission rebuild.

AX-15-56:  The plate is now empty except for the counter gear bearing. Select a socket large enough to tap against the outer race of the bearing. Tap straight to protect the bore. The sand-filler plastic hammer moves the bearing promptly from the plate bore. The case, shift mechanisms and gear assemblies are now all apart. The intermediate plate stands alone in the Bench Mule! 

Measure clearances carefully while rebuilding Jeep AX-15 transmission.

AX-15-57: Here, I move to the subassembly work. Begin with measuring the clearance of gears and thrusts along the main shaft. This is the check for 1st gear side clearance. For first gear, the minimum should be 0.003”, the maximum is 0.0197”—a wide spread. Measure clearances with a blade-type feeler gauge set. Place the feeler gauge blade(s) between the thrust washer and first gear. The thrust washer rides between the rear bearing and first gear.

2nd gear clearance measured on Jeep AX-15 transmission.

AX-15-58:  The 2nd gear clearance is 0.003”-0.0118”, a closer spread than the 1st gear clearance. Use the blade feeler gauges and insert the blade(s) between 2nd gear and the thrust surface machined into the main/output shaft. The feel should be a slight drag on the blade or blades that take up the clearance. This is the side clearance of the gear.

3rd gear clearance measured on Jeep AX-15 transmission.

AX-15-59:  For 3rd gear, you will press the feeler blade(s) between the main shaft thrust and the 3rd gear. This time, you will be on the 3rd gear side of the thrust. For 3rd gear, the clearance is again 0.003”-0.0118”. If the measurement is within specification, the side-face wear of the gear and the thrust will be acceptable.

      Note—The other concern is gear wobble or any looseness between the shaft (or inner race), the bearing and gear. For gear runout, these same three gears, with bearings in place, can tolerate a maximum of 0.0013” measured with a dial indicator. I like to see slightly less than even this small amount—especially with new bearings! Minimum runout is 0.0004”, closer to the expected oil clearance reading for a new shaft, new bearing and new gear. In simple terms, there should be no wobble felt.

Keep track of measurements when working with Jeep AX-15 transmission. 

AX-15-60: These were my findings, noted on the bench top. The 1st gear side clearance is approaching the wide limit but still within specification at 0.016”. (0.018” notation was the blade that would not squeeze into the space.) 2nd gear is better, and 3rd gear is the best. All three gears are within tolerance, and the thrust widths have not been read yet.

Note—If there is any wear at a replaceable thrust, these gears are even more within tolerance. Unless there is tooth damage or too much radial runout (clearance or play) between the main/output shaft, needle roller bearings and the gears, these gears all meet factory tolerances—even at this mileage.

Pilot caged roller bearing used with Jeep AX-15 transmission.

AX-15-61:  The pilot caged roller bearing is a familiar piece in manual transmissions. This bearing supports the nose end of the main/output shaft in the back bore of the input gear. The bore of the input gear, the nose end of the main/output shaft and the bearing itself each determine radial runout and shaft stability. I replace this bearing as a matter of course. Check the bore and nose end for wear and damage. Shaft alignment is crucial to transmission performance and reliability. The crankshaft pilot bearing and transfer case input gear are also involved in transmission shaft alignment.

Removal of output shaft snap ring on AX-15 Jeep transmission.

AX-15-62:  Remove the output shaft snap ring. This is the lock for the 5th gear and bearing. Selective fit, the snap ring aligns the 5th gear and positions the bearing on the output shaft. Keep these parts in sequence and make sure you know their location. You will measure the snap ring with a micrometer or dial caliper if there is a need to replace the ring. Use caution removing the ring; minimize spread and distortion.

Pressing 5th gear and bearing from shaft of AX-15 Jeep transmission.

AX-15-63: The 5th gear is generally tight on the output shaft splines. If you intend to reuse the rear bearing, do not pry against it. I was able to ‘dance’ the 5th gear from the output shaft with the use of my blunt-ended impact driver. Applying force at the output shaft’s end recess while holding the 5th gear stationary, I drove the shaft through the gear with minimal effort and no risk to parts. Easier yet is to press the output shaft through the 5th gear and output bearing at the same time. The press will remove 5th gear, the output bearing and the first gear—all in the single operation shown here. (See my ‘Note’ and ‘Caution’ below.) 

   Note—Press the shaft through the 5th gear and output bearing at the same time. I made a fixture to support the backside of the first gear during the pressing operation. The fixture’s two stands catch the gear’s backside safely without risk of tooth damage. My fixture stands are tall enough to allow the shaft to press out without hitting the press deck. The block of wood will catch the dropped shaft. 5th gear will come off with the bearing and gear. 

     Caution—When pressing the 1st gear, output bearing and fifth gear loose, watch for the tiny locating pin that indexes the first gear thrust washer to the main/output shaft. 1st gear will clear the pin as you press the shaft through the output bearing. Do not damage or lose this pin.

Disassembling the pieces from main/output shaft of Jeep AX-15 transmission.

AX-15-64:  Now the thrust washer, needle bearing, plastic first gear spacer and first gear will slide off the main/output shaft. Note that the thrust washer has a square inner notch that indexes with the pin on the main/output shaft. This finger press fit locating pin is removable—as I discovered the hard way. In washing all parts in my high pressure parts washer, the pin wound up with one of the shift detent pins on the floor of the washer cabinet. Rather than lose or fish for this part, remove the pin from the main/output shaft and set it aside safely. 

Insert plates from 1st gear synchro of Jeep AX-15 transmission.

AX-15-65:  Insert plates (3) at first gear synchro hub are a wear item. Inexpensive, replace them if there is the slightest indication of wear. Access these inserts by sliding the synchro sleeve/reverse gear from the hub. Parts should be marked for their positions if you intend to reuse any of them. Wear patterns may create quirks in shifting if these used parts, especially the brass synchro rings, are not replaced in their original positions.

Snap ring at 1st/2nd synchro hub of AX-15 Jeep transmission.

AX-15-66:  Remove this snap ring at the synchro hub for 1st/2nd gear. The hub is important, as the outer sleeve doubles as the reverse gear. Hub and sleeve wear could cause gear whine in reverse or cause erratic 1st/2nd shifting. Check hub and sleeve closely. Note the condition of the reverse teeth. Chips and damage are generally the result of grinding the transmission into reverse gear without the vehicle stopped. Reverse is non-synchromesh. Drive in a manner that protects this gear. Even a reusable gear will have some wear at the engagement end of the teeth. 

More press work in disassembly of Jeep AX-15 transmission.

AX-15-67:  This fixture is paying off! Here, I safely press against the backside of the free-spinning 2nd gear. Pressure on the main/output shaft, with the 2nd gear backed up, will free the splined first/second/reverse hub from the shaft. The 2nd gear rides on a needle bearing. This use of caged needle bearings at gear running surfaces is high-quality stuff, another impressive feature of these Aisin transmissions.

Caged needle bearing from main-output shaft of Jeep AX-15 transmission.

AX-15-68:  2nd gear caged needle bearing slides off the main/output shaft. Although costlier than transmission types that rely on hard metal-to-shaft surfaces to resist wear, the AX-15 features hard gears, hard roller bearings and hard shafts. The rollers reduce friction for some gains in energy efficiency. Their main purpose, however, is a long-life transmission with replaceable bearings. Although in some ways costlier to rebuild, these transmissions have a high reliability factor! 

3rd/4th gear synchro hub snap ring removal from AX-15 Jeep transmission.

AX-15-69: The 3rd/4th gear synchronizer hub is held in position with a snap ring. Note, again, my use of heavy-duty snap ring pliers. The ring eye, light duty snap ring pliers will not do a good job on these heavy tension transmission type rings. Do not stretch snap rings more than enough to clear the groove. Avoid distorting these rings. 

Press work for splined synchro hub removal on Jeep AX-15 transmission.

AX-15-70:  Again, the splined synchro hub will require the press for removal. The same fixture serves well here, using the 3rd gear as the backer for loosening the synchro hub. Do not damage the gear. Keep fixture platforms outboard of the main/output shaft machined thrust. Note that I catch the back of the gear only. Press carefully against the nose of the main/output shaft. The hub assembly will come free and the shaft drops. Catch the expensive shaft!

3rd/4th gear synchro, 3rd gear and caged needle bearing from Jeep AX-15 transmission.

AX-15-71:  Here is the 3rd/4th synchronizer assembly, 3rd gear and the caged needle bearing. Keep these parts in sequence for inspection and reassembly. If you intend to reuse any synchronizer parts, note their location, especially the brass synchro rings and the hub. 3rd/4th synchro rings generally do not take the abuse of 1st/2nd gear rings. I replace the 1st/2nd synchro rings but often reuse the 3rd/4th rings if there are no signs of wear and they function properly. These are proven, durable parts.

Front bearing snap ring removal from Jeep AX-15 transmission.

AX-15-72:  Work on the counter gear begins with removal of the snap ring that holds the front bearing in place. Heavy-duty snap ring pliers make quick work of this task.

Use of puller for front bearing removal on Jeep AX-15 transmission.

AX-15-73:  A 2-jaw, thin jaw puller will grasp the backside of this bearing. Note that my puller has lateral bolts to prevent the jaws from spreading. This is a universal puller that works well in tighter spaces. The jaw ends are thin, flat and somewhat broad, optimal for this bearing and its close proximity to the gear. I grease the threads to reduce friction and use an impact socket with light air gun force to carefully remove the bearing. Keep the puller from rotating when applying pressure to the screw! 

Front bearing removed from counter gear of Jeep AX-15 transmission.

AX-15-74: The front bearing of the counter gear, the selective fit snap ring and the thrust washer (still on the shaft) are visible. Check each of these parts for wear. Measure the thrust thickness and inspect it for wear. If you replace the snap ring, do so only with a ring of the same thickness—or thicker if the groove and ring indicate play. This is critical to counter gear and bearing alignment.

Removal of front input bearing snap ring from Jeep AX-15 transmission.

AX-15-75: Remove the front input bearing snap ring. You can see that this snap ring pliers has seen some duty. I have even notched and modified its bill to suit unusual applications. Despite removal of material, the quality steel of this tool keeps it intact. If you do a lot of transmission work, invest in transmission snap ring pliers with stout jaws.

Fixture for pressing front-input bearing from input gear of AX-15 Jeep transmission.

AX-15-76:  Pressing the front/input bearing from the input gear requires a fixture. My fabricated fixture works well once more. The force is solely against the backside of the bearing. When removing a bearing in this manner, a great deal of force against the balls or rollers takes place. It is assumed that if you remove the bearing, you will replace it. When installing the new bearing, press only against the inner race. This will prevent loading the rollers or balls within the bearing.

Assemblage of parts from a Jeep AX-15 transmission during rebuilding.

AX-15-77: Well, here it is! This is the AX-15 apart. Every piece is visible except the extension housing. The extension housing mount pad and mount threads had damage, and I will be replacing that section with a good used piece. (See evidence of the damage to this housing at  AX-15-85.) As noted, this is a very “busy” transmission!

Small parts and hardware for AX-15 Jeep transmission.

AX-15-78: Small parts and hardware, special fasteners and critical pieces—these are the crucial parts that need careful tracking. Account for each of them, and set the pieces safely aside. You will need each and every one of these parts during assembly—as I will share in detail.

 Liquid Electric Tape for sealing the backup light switch of Jeep AX-15 transmission.

AX-15-79:  This is a simple fix for electrical insulation/grommets that have deteriorated. Star brite® Liquid Electrical Tape cures to a tough, insulation like material. Use adequate ventilation with this stuff (avoid fumes) and clean the surfaces before applying. You can layer several thin coats to the wire or insulation as necessary. This backup light switch is still in good working order. Cleaned up with fresh insulation on the grommet, it will likely last another 20 or so years!

Checking tolerances of AX-15 Jeep transmission parts.

AX-15-80:  Each one of these parts should be checked closely for wear. You do not want to reopen this transmission any time soon! Do not try to save money by reusing a damaged part. Use good judgment and recall how these parts performed when shifting, under acceleration, and under load in each gear. What you heard and felt is now laying on the bench. This is the time to fix the problems.

Selective fit snap rings and grooves on Jeep AX-15 transmission.

AX-15-81:  Inspect input and other snap rings and check their widths. The width is the selective fit measurement. Press the brass rings against the conical gear hubs, and check for secure braking action. The ability of the synchronizer ring to grip the hub of the gear is what synchronizing gears is all about. Check bearings for roughness—after washing them thoroughly. Spin bearings by hand only, feeling for play, listening for noise and looking for etching or signs of wear or damage. Needles are slightly blue, a sign of fatigue and heat exposure. I will replace these bearings.

Inspecting forks, sleeves, rails and other parts for tolerance and wear on AX-15 Jeep transmission.

AX-15-82:  These are all wear parts. Fork edges, hub and sleeve grooves, rails, bores in the case pieces, arms, links and levers, each is a wear point and demands close inspection. Again, this is the time to replace questionable parts. Bearings should always be checked and compared to a new bearing if necessary.

Reverse idler gear bushing test on AX-15 Jeep transmission.

AX-15-83: The reverse idler gear, oddly enough, rides on a bushing instead of a needle bearing. Wear at the bushing or shaft is cause for concern and will create whine in reverse gear. While this sliding-reverse gear is only engaged and spinning during reverse operation, it does wear. Look for gear tooth damage and bushing wear. The bushing is not a service item; wear demands replacement of the gear and bushing together.

Checking over aluminum cases on an AX-15 Jeep transmission.

AX-15-84:  These cases were extremely oxidized and looked terrible. There was nothing wrong with them, however. I once again used my commercial glass bead blaster, and with an hour’s effort, returned the cases to like-new appearance and function. Make absolutely certain that no glass bead material remains in bores, crevices or castings. I thoroughly washed and flushed these housings after blasting. Hard to believe these are the same castings! 

AX-15 transmission extension housing thread damage requires replacement.

AX-15-85: Here is the original extension housing. I was very unsettled that this AX-15 core came with a broken pedestal and one thread section missing. Although the YJ Wrangler uses only two of these four bolt holes, I elected to find a good used adapter-extension housing. Note that the threads are damaged, with bolt holes wallowed out. The aluminum threads can be repaired readily with Heli-Coil® steel thread inserts. This would be my next step if I were reusing this housing. Aluminum simply will not tolerate abuse—especially over-tightening of bolts or cross threading!

Synchro sleeves are a wear point on Jeep AX-15 transmission.

AX-15-86:  Here is the 5th gear synchronizer sleeve, inserts and retainer springs. Inside the sleeve are the synchro insert plates from the other synchronizers. These inserts are inexpensive and available. Replace them if there are signs of wear. Inspect all synchro sleeves and synchro hub teeth for wear, excess play and damage. Replace questionable parts.

Thrusts and snap ring widths critical on Jeep AX-15 transmission.

AX-15-87:  Measure all thrusts and snap ring widths. This dial caliper is very accurate to less than 0.001” and is a quick means for identifying wear. Clean parts before checking thicknesses. If wear is evident or excessive, and if clearances are too wide, you can replace these thrust washers to close up measurements. The main/output thrust that is built into the shaft would require shaft replacement if worn badly. This is highly unlikely, though, and most worn shafts are the result of poor lubrication or bad bearings. 

Selective fit front bearing snap ring on Jeep AX-15 transmission.

AX-15-88:  Front bearing snap ring is selective fit. This width controls the location of the gear and the tight fitment of the bearing against the gear. The rule here is to always use the snap ring that will completely fill the width of the groove. You must keep the bearing flush against its stop. If the snap ring is loose or shows clearance in the groove, replace it with a thicker width snap ring. This is not likely at the front bearing, as the bearing is a firm press onto the shaft, and the snap ring simply keeps pieces in place. Use the original width snap ring as a starting point.

Checking shaft runout on V-blocks: AX-15 Jeep transmission.

AX-15-89:  Check shafts for runout and “true.” A pair of V-blocks will support the shaft as you rotate it. Use a dial indicator with a roller end if necessary. Here, I am using a non-roller end to get initial measurements. When switching to the roller end, I can rotate the shaft and check the amount of runout. Maximum allowable main/output shaft runout is 0.0024”, a relatively small amount if measured with the V-blocks placed at the shaft ends. Less than this amount of runout is desirable and expected.

Removing material from output shaft of AX-15 Jeep transmission.

AX-15-90: This is an extra step for using an Advance Adapters’ Atlas II transfer case behind the AX-15 transmission. Installation calls for removal of 0.125” of material from the end of the output shaft. Several commercial tools will accomplish this: an industrial (liquid cooled) band saw, a belt sander, lathe, or a surface grinder with holding fixture. I elect to use my reliable chop-saw with a fresh blade.

     Caution: I avoid forcing the cut, as this would heat the metal and destroy original and essential heat treating of the shaft and splines. My commercial tool of choice would be a liquid cooled band saw if there is enough material to allow the blade to make a groove and not run off the end. Operate the band saw at a slow cutting rate.

Avoid heating the shaft during shortening process: Jeep AX-15 transmission.

AX-15-91: Slowly moving the blade to avoid overheating and deflection off the end of the shaft, I gradually work my way through the shaft. Check measurement often. If you use a cut-off saw like this, watch for signs of heat discoloration. Move the blade up and down frequently to keep the cut true. The blade will want to move outward with an end cut of this kind. I spent half an hour slowly cutting this end, patiently allowing the blade to find true alignment and watching the sparks to determine material resistance and the amount of heat applied. 

     Warning—To protect heat treating, check the degree of heat frequently with an infrared surface temperature meter or gun. Always wear goggle-type eye protection when working with cutting or grinding equipment of this kind!

Trimmed end of output to accommodate an Atlas II transfer case with this Jeep AX-15 transmission.

AX-15-92: Yes, this is really the same shaft! After cutting the end flush and squaring up the face, all with the chop-saw, there were no signs of bluing. I used my bench grinder and platform to very carefully “chamfer” the spline teeth in a uniform, lightly raked pattern. (This will enable easier transfer case input engagement during fit up.) The material grinds easily, so if you attempt to do this, use extreme care and a steady hand to bring the shaft to the grinder and rotate the shaft uniformly at the same angle. A belt sander would be a practical alternative. 

     Note—This finished shaft end measures square, and there is no risk of an “imbalance” from removing material this far back of the rear bearing. Note that there is no “bluing” or indication of heat impact on the shaft end. Uniform chamfers make the spline ends nearly identical to the original shaft, although I made a steeper rake to minimize the amount of material removed from the splines. If you are not sure of your tooling or ability to do this, consider subletting the task to a machine shop. If you install an Atlas II transfer case, follow the most up-to-date instructions from Advance Adapters before modifying expensive parts like an output shaft! Take measurements carefully for a correct and safe fit-up of the transfer case input.

Click here for Rebuilding the Jeep AX-15 Transmission, "Part 2". Get close-up details on assembling the AX-15 to function as new! 

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 interested viewers to the 4WD Mechanix Magazine website at: www.4WDmechanix.com. As copyrighted material, this article and the photography cannot be copied or distributed in any other form. Thanks!—Moses Ludel

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