How-to: Rebuilding a Jeep AX15
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
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
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
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
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!
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
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.)
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
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.
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.
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
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
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
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.
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.
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.
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
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.
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
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.
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.
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.
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
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.
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
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
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.)
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
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.
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
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.
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.
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
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.
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
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
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
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
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.
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.
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!
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.
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.
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.
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.
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.
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.
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
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.
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
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!
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.
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
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.
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
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
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.
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
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.
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.
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
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.
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.
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
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.
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.
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
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
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.
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
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.
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.)
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
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
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
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.
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
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
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
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.
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!
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,
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.
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!
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
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.
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
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
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.
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!
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.
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
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.
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.
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
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!
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
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.
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
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.
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
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
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
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
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
Click here for
Rebuilding the Jeep AX-15 Transmission, "Part 2". Get close-up details on assembling the AX-15 to function as
2010 © Moses Ludel...Enjoy this comprehensive, color-illustrated article and photography by Moses Ludel. The
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