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
4WD Hardware has a blow-out diagram and available parts listing for the
AX-15 transmission. For direct access online, click here!
Note: You can gain a valuable
understanding of the AX15's functions by watching this
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. In particular, the "earlier" versus
"late" 3rd/4th gear synchro parts get discussed thoroughly,
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 1st/2nd rings as a matter of course on a five-speed
manual transmission. There was no appreciable wear on the 3rd/4th and 5th 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
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
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
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
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
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
1st gear (right) and
2nd 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
1st/2nd 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 1st/2nd 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 1st/2nd 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 1st/2nd 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.
1st/2nd synchro plates are reversible, too.
AX-15-109: This is the
1st/2nd gear assembly together. Note that the 2nd 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
2nd and reverse gear
functions. This is a considerable load and requires strong parts with close
AX-15-110: This is the
3rd-4th 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 3rd 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 1st/2nd and 3rd/4th gears on the AX-15
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
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 3rd 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 3rd 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 3rd 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-15-119: The 2nd 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 2nd 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 1st/2nd gear synchronizer
AX-15-121: Now I press the
1st/2nd 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
AX-15-122: Install the snap ring onto the
main/output shaft. This secures the synchro hub for 1st/2nd 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 1st 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 1st gear side of the hub. Keep the sleeve/reverse gear centered on the synchro hub. Install
the 1st 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
AX-15-126: Slide the
1st 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 1st 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 1st 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 5th 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
AX-15-130: The 5th 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
4th 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
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
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
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 1st/2nd 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
AX-15-145: As you slide the
1st/2nd shift rail through the intermediate plate, make sure the interlock pin stays in place.
Catch the lower hole of the 1st/2nd 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 1st/2nd gear shift rail. Make sure the interlock plug seats.
AX-15-147: Now the
3rd/4th shift rail slides through the intermediate plate. It picks up the upper hole in the
1st/2nd shift fork before reaching the 3rd/4th shift fork bore. Lift the
3rd/4th 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
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
AX-15-150: Slide the
5th 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
5th gear rail need
only pass through the intermediate plate enough to hold the lock ball above the 5th gear shift rail. This interlock ball serves
between the 5th gear
rail and the reverse shift rail.
AX-15-151: Move to the back of the
intermediate plate. The 5th 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
5th 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
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
AX-15-155: This is the entire counter
5th gear and
synchronizer assembly ready for installation on the cluster/counter shaft. (The 5th 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
AX-15-156: The bearing at the counter
5th 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: 5th and counter 5th gears are now aligned and engaged. This is the 5th gear/overdrive system. The brass
synchronizer ring is similar to the rings used at the 3rd/4th gear synchro
AX-15-158: At this stage, the 5th 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 5th 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
5th 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 5th 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
(5th gear) rail,
interlocking between the reverse shift head’s rail and the 5th gear rail. Use petroleum jelly to keep the
ball in its bore. (The 5th 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
5th 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
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
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
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
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
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
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
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
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
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
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
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
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
AX-15-179: Here is the sealant bead
on the surface of the front bearing retainer. Make sure the seal is in place! A 1/8th 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
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
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
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 1/8th 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
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
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
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
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
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
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
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
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
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
Adapters Atlas II transfer case. The stock stick-out length will, of course, be
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,
5th gear on the
main-output shaft faces the greatest load— yet this is the smallest gear of the forward speeds. Use
5th gear prudently,
and avoid overloading or taxing the 5th 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