AX15 Rebuild: Complete Step-By-Step Guide

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Introduction:

Rough shifts, clapped out syncros, grinding gears: AX15 Rebuild time. 

While the AX15 is an overall robust transmission, high road miles and hard off-road miles take their toll. Time for a trip to the repair shop?

Not necessarily. With a solid plan in place, a manual transmission rebuild is a worthy project for the garage mechanic. Read through this step-by-step rebuild guide to know just what an AX15 rebuild entails.  

Workspace used to rebuild AX15 transmission at home DIY in the garage
Disclaimer: I’m no professional. I hadn’t built transmissions before this writeup. But I do struggle with the concept of emptying my wallet on repair bills. Why pay someone to do the same work I could with a little know-how and time spent in the garage? 

This article serves as an in-depth tech writeup. A full detail AX15 transmission rebuild guide including step-by-step pictures. Plus, a few references to the better build videos and service manuals out there. The same ones that got me rebuilt and back on the road in no time. 

I knew the value of a fresh rebuild, after years of limping around a thrashed AW4 automatic transmission in the 2000 Cherokee Build (before it got swapped to the AX15). A tired gearbox can quickly become the weak link when hitting the trails and will grenade itself if existing issues are overlooked.

At the first sign of shifting or gear issues, an inspection and rebuild may be in order. Here’s the run down on a DIY rebuild:

Jeep AX15 Swap Rebuild Kit With Bearings, Gaskets, Replacement Parts Installed On 2000 Jeep Cherokee

Prep & Parts: 

If you’ve landed here – I’m going to assume your transmission is already overdue for a rebuild. Sticking gears, rough shifts, and metal in the fluid all indicate greater problems to come.

Everything you need to knock out a full overhaul in the garage:

AX15 Rebuild Parts List

Before reading up on the rebuild steps you’ll want to map out a parts and tools list. 

The rebuild process requires a few specialty tools beyond your typical toolkit (socket set, wrenches, etc). Make quick work of it with the right tools:

Tools Required For Manual Transmission Rebuild:

  • Fullsize Shop Press (Bearing Removal & Install)
  • Wrenches: 27mm, 24mm 12mm, etc.
  • 10mm allen wrench socket, Torx 40 socket
  • Hex socket set, extension set, u-joint extension
  • Large pry bar & rubber mallet
  • Channel locks, needle nose pliers, magnetic removal tool
  • Snap ring pliers / removal tool
  • Two equal length flathead screwdrivers (snap ring removal)
  • Bench vise (holds things in place during rebuild)
  • Bearing splitter
  • Feeler gauge (for tolerances of bearing/gear install)
  • ½” Torque Wrench and/or ⅜” Torque Wrench
  • Transmission Jack or Floor Jack, Ratchet Straps, Scrap 2×4 Wood

Additional Helpful Tools:

  • Battery Powered ½” Impact Gun 
  • ½” and ⅜” Breaker Bars, Metric Impact Socket Set
  • Oil Fill Pump Kit
  • Sharpies & Lots of Zip Lock Bags (Label EVERYTHING as it’s removed)
Tools required for AX15 transmission rebuild and swap into Jeep Cherokee XJ 2000
Ready To Wrench: Clean Workspace, Organizer Bins, And Ziplocks.

Pro Tip: Some of the tools needed (bearing pullers) can be rented from local auto parts stores (at no cost). Still, good tools are a good investment.

Supplies/Fluids:

  • Vaseline (for packing/greasing bearings)
  • Brake cleaner, degreaser (cleans outside of case well)
  • Transmission fluid: MT-90 transmission fluid or 10W30 synthetic oil
  • Replacement Oil Fill Plug & Crush Washer
  • Complete AX15 rebuild kit (bearings, syncros, gaskets/seals, etc)
  • Oil-Resistant RTV Gasket Maker
  • Replacement gears & parts as needed (chipped/broken teeth, catastrophic failure)
  • Replace While In There: Clutch Kit, Throwout Bearing, Master & Slave Cylinder, Manual Transmission Mount, Shift Boot, Shift Knob, Clutch Pedal Pad, Etc.

Sourcing AX15 Parts: Low-Cost Vs. High-Quality

The list above includes a mix of parts that can be sourced on the lower-cost side, and some that you won’t want to skimp out on. While I always start with local parts stores for selection and service in one, there’s a few other sources that I’ll frequent. RockAuto is a good source to check as well as Summit Racing.

If you are going the quick and easy route of Amazon or Ebay, you’ll want to give a second look at part numbers and compatibility. A wrong part can quickly throw a wrench at things during install.

AX15 install replacement transmission after rebuild installing into 2000 Jeep Cherokee Sport Manual Transmission

AX15 Transmission Removal:

The exact steps for removing the transmission from the Jeep will vary between models (Wrangler, Cherokee, Comanche, Etc). It’s best to consult a model-specific service manual to understand the step-by-step removal. 

The overall process remains the same: drain all fluids, disconnect all wires and shifter components (see below) and support the transmission (transmission jack or floor jack setup). Continue to remove the driveshafts and transfer case (4WD) as well as slave cylinder and clutch assembly.

Finally, while supported, unbolt the transmission bellhousing from the engine block and carefully remove. 

Sidenote: Specific to the Jeep Cherokee XJ there are two E12 Torx bolts that are often a pain to access (upper bellhousing to engine-block connection). Make sure to have an E12 socket on hand for removing these.

AX15 Rebuild Step-By-Step Guide:

AX15 factory service manual rebuild instructions with diagrams PDF link document free
AX15 Factory Service Manual Reference (No Affiliation With Craftsman Collaborative)

Before You Start: Prep Items

  1. Print out the full AX15 factory service manual – step by step guide.
  2. Clear a clean workspace – organization is king on any rebuild.
  3. Buy a healthy-sized box of zip lock bags and a sharpie or two.
  4. Keep a camera/phone on hand to take reference pictures as you go
Garage rebuild workspace for AX15 rebuild Jeep Manual Transmission Rebuild Kit Install DIY Home Garage

With the transmission removed, place it on a workbench and start disassembly. As each part is removed, label it, put it in a zip bag and organize it in order of removal. A well kept workspace is crucial here.

While the writeup below provides an expanded take on many items, the factory AX15 manual is unbeatable for its to-the-point steps during rebuild.

AX15 Rebuild Video Tutorial / How-To

The sections below detail each portion of the rebuild with step by step photos and instructions. It can be helpful to reference a rebuild video as well, here’s a detailed one we referenced throughout the build:

Youtube: @Ucandoit2 (Video Credit, No Affiliation With Craftsman Collaborative)

Removing Electrical Connections

The only electrical connector on the AX15 is the reverse light switch. Remove using a 27mm wrench, the full sensor assembly threads into the side case.

AX15 transmission rebuild removing reverse light switch sensor and replacing on 1998 Jeep Cherokee XJ

Removing The Shift Lever

This will likely be done before dropping the transmission out of the vehicle, but in any case we’ll detail it quickly here. The shift knob is threaded on and can be unscrewed with a counter-clockwise (lefty-loosey) motion.

Next, lift up the round rubber boot at the base of the shifter, exposing the metal locking mechanism. This metal keeper is spring loaded and needs dislodge by pressing down and turning an 1/8 turn to the left. It should pop up and allow the shift lever assembly to be removed, including the bushing.

It’s a tough one to describe – here’s a helpful video to give a better idea:

Youtube: “Power Addicts” (Video Credit, No Affiliation With Craftsman Collaborative)

Shift Tower & Pivot Rod Teardown

Looking down at the top of the transmission, loosen the 4 bolts securing the shift tower and lift it off (use a light mallet tap or pry bar as needed).

Shift lever base and gasket replacement rebuild install on AX15 manual transmission Jeep

In the pictures, the shift lever was left on. It can be removed prior as above.

Remove the two shift detents threaded in on either side of the shift tower base (24mm). These are the large blocky hex-head inserts pictured below.

Shift arm assembly and positioning with side detent plug pin bolts in place AX15 transmission rebuild Jeep

Remove the 12mm bolt securing the shifter arm (central bolt inside of the shift tower pictured above)

Rear view of output shaft and rear case on AX15 manual transmission using 10mm allen head hex plug to rebuild.

Remove the 10mm hex plug on the rear of the transmission, to the side of the output shaft (pictured to the left above).

With the rear plug removed, work the shift arm shaft rearwards. A screwdriver is initially helpful here (be careful not to use much force).

A magnetic tool can pull the arm the rest of the way out from the rear case.

Shift arm removal on AX15 rebuild Jeep Manual Transmission Service

The shift arm should now be lifted out of the shifter base and set to the side.

Rear Transmission Case Split/Removal

Location of detent ball detent plug on AX15 transmission rebuild with Torx 40 plug tool

Remove the detent plug/ball from the rear case. This is the Torx 40 plug, located in the center/upper/right of the photo above (between the two long case bolts). There will be both a spring and ball bearing inside of the plug. Use a magnetic tool and be careful not to lose the detent ball.

Noting which direction bolts go on an AX15 rebuild for a 1998 Jeep Cherokee Manual Transmission

Continue to remove the series of bolts connecting the rear case and center. These were numbered/labeled on our rebuild to keep in place.

Using a mallet and/or pry-bar, knock the case loose. It shouldn’t take much force, as only a thin layer of RTV / Gasket-maker is holding things in place.

Output shaft and 5th gear teardown on 1998 AX15 rebuild for Jeep Cherokee XJ

The output shaft and rear components will now be exposed. This is the first chance to inspect for worn teeth/splines and any additional parts needed.

Bell Housing Removal

Remove the slave cylinder with the 2 fasteners pictured above (this may be done prior to transmission removal). Additionally, remove the opposite side fastener that goes through to the clutch fork/ shift lever.

Original bellhousing and throwout bearing clutch fork on 1998 Jeep Cherokee XJ transmission replacement

Pull the throwout bearing and clutch fork from the input shaft. Continue to remove the series of bolts inside of the bell housing that secure it in place.

Front Transmission Case Split/Removal

With the input shaft cover exposed, remove the bolts holding it in place. This piece is held in with a bit of RTV and will need a light pry to come loose.

AX15 manual Jeep transmission with bearing plate removed and bellhousing removal completed looking at input shaft.

With the bearings exposed, there are 2 snap rings that will need removed. These clip into each of the bearings and secure them within the front case.

With the snap rings removed, the case can now be unbolted and separated by tapping/pulling forward, away from the bearings and center assembly.

With the bell housing, front, and rear cases removed we now have full access for inspection and rebuilding the inner works of the transmission.

AX15 Rebuild Inspection – What To Look For

The build pictured in this article was sourced from a 200k+ mile 1998 Jeep Cherokee at the local pick and pull. After dropping it from the vehicle, we cycled it through the gears by hand, while manually spinning the input shaft, and no gears felt locked up or otherwise noisy.

With no idea of the service history, we split it open as a wildcard on whether we’d need to replace any gears or parts beyond the standard rebuild kit.

Once we reached this point in the rebuild, we again looked over all components for any sign of metal on metal wear. Check gears for gouged or missing teeth, shift rods for any visible bends or alignment issues.

We lucked out with our rebuild just needing syncros and bearings, but each case will be different. If you queue up the video below from Mike/Ucandoit2, you’ll get an idea of what a damaged gear does look like on his AX15 rebuild:

Youtube: @Ucandoit2 (Video Credit, No Affiliation With Craftsman Collaborative)

Intermediate Plate Set Up

With the cases split, it’s time to tear into the gear set and bearing assemblies for further service. A quick trick here is to clamp things down in a bench or drill press vise to keep the transmission secure.

Be sure to use a bolt and nut through the bottom two holes of the intermediate plate to clamp into the vise. Avoid damage – do not clamp onto the mating surface directly.

Detent Ball Removal – Intermediate Plate

On the intermediate plate, there are an additional 3 detent covers/balls, beyond the one that was removed prior in the rebuild. These use a T40 Torx bit for removal. Once the cap is removed there should be both a spring and a detent ball inside. The ball may need removed with a magnetic tool.

The three detent plugs are pictured below, on the left side of the case:

Complete factory gear set on 1998 Jeep Cherokee Manual Transmission Rebuild AX15

5th Gear Shifter Assembly & Syncro Removal

Gear removal after using a gear puller to remove 5th gear shifter assembly on AX15 Jeep Cherokee Transmission
Pictured above with the 5th shift hub snap ring removed and syncro accessible.

The 5th gear is on the rear side of the intermediate plate, mated up onto the output shaft. The shifter assembly (syncro, syncro gear, shift fork, hub) is coupled below the 5th gear, on the lower gear shaft.

Remove the snap ring on the rear of the shifter assembly shaft (pictured above after removal).

Tip: Using two equal size flathead screwdrivers, line up the tip of each on the snap ring and tap both handles with a mallet to force the ring down.

Rear of AX15 output shaft with 5th gear removal during Jeep manual transmission rebuild DIY project

Next, remove the 10mm bolt from the shift fork. Pictured above, this bolt is to the front right side , securing the shift fork on the lower gear set to the rod intersecting the intermediate plate.

Use a standard gear puller to thread into the outer syncro gear face and remove. The syncro ring and outer gear can be removed and set aside.

Important: All pieces removed are directional. Be sure to mark which direction they face during removal. A sharpie or piece of tape with an arrow towards the intermediate plate makes a good note, take pictures too!

Syncro ring removal on AX15 rebuild 5th gear shifter assembly replaced with a rebuild kit on 1998 Jeep Cherokee XJ

The shift fork and hub that meshes over the gear can now be slipped off. Be mindful of the needle bearing in the hub, this will be replaced later on.

The 5th gear will be free to remove as well as the spacer washer behind it. There is a small ball bearing piece engaged in this shaft that needs to be saved and realigned during reassembly.

Main Shaft/ Reverse Idler Gear Removal

Remove the 4 forward facing bolts that secure the main shaft retainer in place (removed in picture below). Pull off the retainer plate and set aside.

AX15 output shaft with rear bearing retainer in place and rear cas removed during AX15 transmission rebuild
Reverse gear rod placement with fastener head securig with bearing retainer plate on AX15 rebuild Jeep Manual Transmission 1988 to 1999
The rod face pictured above is notched to lock into the retainer plate.

Moving to the front side of the intermediate plate (input shaft side), remove the reverse counter gear and idler shaft off by sliding it forward out of place.

Reverse gear inspection on Jeep AX15 determining when to replace a gear during the 1998 Jeep Cherokee AX15 Rebuild
Reverse gear shifter arm mechanism close up in AX15 rebuild manual transmission replacement part install on 1998 Jeep Cherokee

On the opposite (left) side of the idler shaft, locate the shift arm pictured above. Remove the two bolts securing it in place to the intermediate plate. Remove the bracket: The upper shift arm pivot point will slip out of place freely once the two bolts have been removed.

Next remove the shift arm by disengaging the spring clip on the lower pivot point and sliding out of place.

Shift Rod Removal

Remove the reverse shift head and rail located on the end of the shift rods (output shaft/rear side). This involves sliding the rod until the detent ball aligns – again you’ll want to watch a video clip of this to make it make sense:

Youtube: @Ucandoit2 (Video Credit, No Affiliation With Craftsman Collaborative)

With the reverse shift head removed, continue onto the shift rail removal. Again, this can be finicky with the detent pins and plugs that secure the rods in place. These detent balls can be of different sizes/shapes, so be sure to note which goes where as removing them and labeling/bagging.

The process here is best summarized in the AX15 factory service manual.

AX15 Rebuild Factory Service Manual Depicting Shift Rail Ball Plug Pin Position Placement And Removal
Shift Rail Detent Ball/Pin Chart – Factory Service Manual

Referencing the Factory AX15 Service Manual shows further diagrams here all those little interlock components can sure get your head spinning.

Sidenote: it is also possible to rebuild the AX15 without removing the shift rods from the intermediate case, and altogether avoid the interlock plug removal. More info on that in our FAQ section here.

Main Shaft & Cluster Gear Shaft Removal

With the shift fork and rods removed (or worked around as noted above) continue to remove the gear sets from the intermediate case for service.

There are two additional snap rings securing the intermediate plate bearings for each shaft in place. Locate these snap rings on the output shaft side of the intermediate case and remove with snap ring pliers.

Once the snap rings are removed, a light mallet tap is all that is needed to separate the two shafts from each other and the intermediate case.

Factory gear set shafts removed on 1998 Jeep Cherokee XJ AX15 Manual Transmission Preparing For Rebuild
Close up of input and output shaft connection on 1998 Jeep Cherokee XJ AX15 Rebuild DIY Project

The main shaft will easily separate into two sections – with a split between the input and output shaft sides. Carefully pull apart the sides and note the orientation of the syncro ring nested between.

Splitting the output and input shaft sides of the transmission gearset on a Jeep AX15 rebuild

Removing Syncros & Gears From Shafts

You’ve made it to the midpoint! It may feel like a lot, but with the transmission in front of you and a good organization system, it is a manageable series of steps. Now that we’ve gotten the full transmission apart down to the gear sets, we can replace the syncro rings and bearings.

If any replacement gears are needed, this is the time they can be swapped.

Factory bearing on AX15 input shaft being removed for replacement with a rebuild kit

Using a bearing splitter, press off the bearing from the input shaft. Replace it with the bearing from the rebuild kit, following the same orientation. Continue to reinstall the necessary snap rings, double checking alignment.

The main shaft will require more steps, but in a similar fashion: Remove the series of snap rings and bearings as well as gears until the shaft is stripped.

There is an alignment pin that will need kept in a safe place (don’t lose this).

It is also worth a reminder that most all of these gears and bearings are directional – use a sharpie or label to note the direction of each as you remove. Also pictures, lot’s of pictures.

Stripped and cleaned Gear Set input shaft and output shaft with gears removed on AX15 Rebuild
Both gear set shafts, stripped of bearings and gears. Ready to rebuild.

While in the midst of the rebuild, I didn’t get a good batch of photos of the gear set removal. It goes quite quick with good organization.

We followed the Youtube video referenced throughout this article, and recommend watching through the next video in the series as well. The series continues on to show the step-by-step removal of gears and bearings on a garage shop press:

Youtube: @Ucandoit2 (Video Credit, No Affiliation With Craftsman Collaborative)

Replacing Gears & Bearings

Once the gear set shafts have been fully pulled down and cleaned up, reinstall can begin. With the position and order of each gear noted from removal, reinstall in roughly the reverse order of removal. While most complete AX15 rebuild kits should include the major bearings and syncros, always double check the old and new parts match before install.

We went with Mobil 1 10-w 30 oil for our AX15 transmission fluid choice, and gave a quick soak of each bearing just before install as an extra step.

AX15 Input Shaft Rebuilt With New Bearing and Syncro Snap Ring Install
Using a shop press to remove and reinstall gears and bearings on 1998 Jeep AX15 Transmission Rebuild

We used the shop press to press the bearings and gears back into place. Careful to use the lightest amount of force needed to avoid any bent or broken pieces, the replacement components should slide right in.

The gears need pressed just far enough to allow for the snap ring to seat.

First Gear and Second Gear Service Replacement Syncro During AX15 Rebuild on 1998 Jeep Cherokee XJ Transmission

The single most important thing that kept this process headache free was noting the direction and order of all the parts during removal. We’d bag them and sharpie notes in which order and direction each piece fit, as well as referencing the photos that have become a part of this writeup.

For more detailed walk-throughs of each bearing removal/ install, again reference the AX15 rebuild video above – this covers it better than anywhere.

Pictures of more detailed parts of the gear install (click to enlarge):

With our rebuild kit, we did note a slight variation in the replacement pieces for the gear hub assembly pictured below. One of the inserts was different in length than both the originals and two others in the rebuild kit. Odd!

Writing it off as a wrong piece from the factory, we ended up using one of the original inserts as it was in perfectly usable condition. Good reminder to check all parts before blindly installing – compatibility issues do happen.

Rebuild Kit Issue Noted On AX15 Rebuild Kit For 1998 Jeep Cherokee XJ Transmission Gear Hub Key Insert

Stripping & Cleaning The Cases

Cleaned Stripped Aluminum Cases on AX15 Manual Transmission Rebuild Scotchbrite Degreaser 1998 Jeep Cherokee XJ Transmission Case

With the transmission pulled apart, it’s an opportune time to get in there and give everything a full clean for that factory fresh finish. Using a spray degreaser, scrub brush and a few other tools had things looking good as new. Do take caution not to leave any crumbs from Scotch-Brite pads, etc.

Replacing Intermediate Case Bearings

With the case cleaned up, the replacement bearings should slide right in place. Reinstall the snap-ring as removed earlier.

Gear-Set & Shift Fork Install

Applying break in oil Mobil 1 10W-30 motor oil on rebuilt AX15 transmission gears and bearings

With all parts cleaned and the gear-set shafts reassembled, the install continues as the reverse of removal – see the factory manual for details.

AX15 Rebuild/ Reinstall Video

Part 3 of this youtube series covers in detail the reinstall process with step-by-step narration. Doesn’t get more helpful than this:

Youtube: @Ucandoit2 (Video Credit, No Affiliation With Craftsman Collaborative)

Transmission Case Assembly

With a final inspection and bearing clearances/tolerances measured (detailed in factory manual and video above) the transmission is ready to bolt back together, fill with proper spec transmission fluid, and drive.

With the mating surfaces cleaned, use an oil-resistant RTV to seal things back up, making sure to get full coverage around all fastener points.

Rebuilt AX15 transmission case install with finished rebuild and new RTV gasket maker sealant.

Bellhousing, Clutch Fork, Throwout Bearing Install

With the transmission rebuilt, sealed and assembled, reinstall the bellhousing with the set of inner bolts removed earlier. Reinstall the clutch fork as well as a new throwout bearing for added assurance.

Replacement clutch fork and throwout bearing installed during AX15 rebuild manual transmission on 2000 Jeep cherokee

While You’re In There: Items To Replace/Upgrade

With the transmission already dropped, it’s an ideal time to replace the clutch assembly, pilot bushing, and bleed/replace the master and slave cylinder as needed.

As we were swapping from auto to manual transmissions on the XJ, we already had the flywheel removed. Some brake cleaner get’s it ready for the new clutch install real quick.

Final Transmission Install: Last Items to Check

With the transmission assembled and ready to install, it’s a good idea to reinstall the shifter assembly and make sure each gear shifts and engages freely. Spin the input shaft with each gear engaged, stop, shift to the next gear, and continue. Make sure no grinding/jamming is present.

If anything feels off, reference the notes and pictures from your teardown/install and isolate the issue to the select gear/parts.

A quick teardown and inspection is much better now, before the transmission is fully installed.

Rebuilt AX15 Transmission complete assembly ready to install in Jeep Cherokee XJ

With the final shift test out of the way, the AX15 can be lifted into place, aligned with the clutch assembly and bolted back up to the engine.

We opted to add our choice of AX15 transmission fluid once things were lifted in place – and that’s all. The rebuild is ready to get some miles on it!

AX15 Rebuilt Transmission Installed With Floor Jack On 2000 Jeep Cherokee XJ

Still have questions/confusion around the rebuild terms or details?

AX15 Rebuild FAQ’s

The time required for an AX15 rebuild varies depending on the skill/experience of the mechanic.

As a first time rebuilder, it took us a few spaced out days to rebuild at our leisure.

For a more ambitious tech, the project could be completed in or around a single day, with all parts on hand and the process dialed. We’ve seen practiced rebuilders claim 4-6 hours with the unit removed, if all goes smoothly.

Note the time required to drop the transmission, teardown, inspect, rebuild, and install. This time also varies on the detail of cleaning cases/parts, installing added parts like a clutch kit, and the condition of the donor transmission.

Look for a complete rebuild kit with all serviceable gaskets, bearings, and syncro rings included.

Our set was sourced from an independent eBay seller, and came with Japanese-made bearings (Nachi).

Simpler (low-cost) rebuild kits include the minimum bearings and gaskets.

Full service (master) kits include everything from needle bearings to shifter bushings.

We went with a full service AX15 rebuild kit similar to this one. 

Beyond the rebuild kit and parts list detailed above, the parts required will depend on the condition of the donor transmission. A good-condition high mileage AX15 will likely need just the rebuild kit w/ syncros, bearings, and fluids.

An AX15 with metal in the oil or clunky gears may require a replacement gear, on top of the parts noted above.

A general plan is to source a full service AX15 rebuild kit, and inspect the gear sets during teardown for replacement. If you know a specific gear is blown out, this gear can be ordered in advance.

Whether rebuilding or changing fluid on an AX15, you’ll want to avoid specific fluid types that will cause harm to the transmission’s syncro gears. Newer manual transmission fluids (GL-4 or GL-5) often contain higher sulfur contents that destroys these brass synchronizer rings.

Opt instead for a syncro-safe fluid. Many AX15 / Jeep owners report good luck with the Redline MT-90 manual transmission fluid. A synthetic 10W-30 motor oil can be used as well, as we did in our rebuild.

While the AX15 originally called for GL-3 manual transmission fluid, Chrysler updated the service spec to use synthetic 10W-30 motor oil some years later as GL-3 was superceded by GL-4 and GL-5 formulas (see above issues with these).

10W-30 Synthetic Motor Oil is regarded as a safe and preferred option for AX15 rebuilds and service.

We used Mobil-1 Synthetic 10W-30 oil in our rebuild, with no complaints. There are a fair amount of Jeep owners on the forums that report the same.

10W-30 motor oil or MT-90 Transmission Fluid: Which is the better choice for an AX15 rebuild or fluid change?

While Redline MT-90 has a solid reputation among Jeep owners with an AX15, a synthetic 10W-30 motor oil comes at a fraction of the cost. Both have been used with few reported issues, make your choice.

On our ’98 AX15 rebuild, we went with Mobil 10W-30. Not only did it provide a proven and affordable option, but it matches the same spec motor oil we run in our 4.0 engine. So? One less fluid type to pack for off-road trips – keep it simple!

For a DIY mechanic, an AX15 rebuild typically costs between $350 – $500+, including a rebuild kits, fluids, and other parts. If the transmission requires a gear replacement, this cost will run higher.

At a shop, the cost will depend on their labor rate and time billed to drop the transmission, teardown, rebuild, and reinstall. We’ve heard a ballpark ~$2000-$3000 number thrown around but it really depends on the shop (independent vs. dealer) and hours billed. There may be a Jeep-specific rebuilder in your area that will do it for less with the transmission removed.

While an AX15 rebuild will service the original transmission, there is also the possibility of swapping a new unit in its place.

The most reputable source comes from Advanced Adapters, who sell a factory-new AX-15 for ~$2100.

(Note, this AX-15 is specced for Wranglers and will not install without modification into an XJ Cherokee)

There are also a number of remanufactured units available online that range from $1300-$1600. Lower cost rebuilds may be found on eBay or locally, but take caution in reading vendor reviews and warranties before buying.

In addition to our AX15 rebuild tech write-up, where we note each stage of the process, we recommend the Factory Service Manual. This rebuild manual provides detailed AX15 rebuild instructions, illustrations and specs.

Find a .PDF of the AX15 Factory Service Manual Here.  

When preparing to tear into our AX15 rebuild with zero transmission experience, we found the Youtube series from Mike at Ucandoit2 to be unmatched. The series covers his garage rebuild step-by-step with reference to the factory service manual. Find the AX15 rebuild series here:

Youtube Channel – Ucandoit2

AX15 Rebuild Part 1 – Youtube Video Covering Teardown

AX15 Rebuild Part 2 – Rebuild & Gear Install

AX15 Rebuild Part 3 – Final Assembly & Bench Test

While we opted to remove the shift rails during our AX15 rebuild, this is not always necessary. As long as there are no issues with the movement of the shift rails and detent pins, the rebuild can be done with the shift rails intact.

After completing our rebuild, we found an article by Mean Max on Jeep Forum that details just this.

From the AX15 Factory Service Manual:

Shift Fork Set Screws: 20Nm (14 ft. lbs)

Lock Ball (Detent) Plugs: 19Nm (14 ft. lbs)

Reverse Shift Arm Bracket Bolts: 18Nm (13 ft. lbs)

Front Bearing Retainer Bolts: 17Nm (12 ft. lbs)

Rear Case / Housing Bolts to Intermediate Plate: 37Nm (27 ft. lbs) Apply silicone/sealant to threads.

Shift Arm Set Screw: 38Nm (28 ft. lbs)

Shifter Base Restrictor Pins: 19Nm (14 ft. lbs)

Shift Arm Shaft Access Plug: 19Nm (14 ft. lbs)

Shift Tower / Shifter Base Attachment Bolts: 18Nm (13 ft. lbs)

Reverse Light Switch: 37Nm (27 ft. lbs)

Transmission Fluid Oil Drain Plug: 37Nm (27 ft. lbs)

Clutch Housing to Transmission: 37 Nm (27 ft. lbs)

Clutch Housing to Engine: 38 Nm (28 ft. lbs)

Transfer Case to Transmission Nuts/Bolts: 35 Nm (26 ft. lbs)

Crossmember to Frame Bolts41Nm (30 ft. lbs)

AX15 Transmission Rebuild Outcome

We did a DIY garage rebuild of this ’98 AX15 to swap into our automatic XJ. As a first time transmission rebuilder, the process went smooth with plenty of research ahead of time, a thought out process to follow, and appreciation of OCD in zip bagging and labeling each and every part in order of removal.

The AX15 rebuild worked well with our selected rebuild kit. While the transmission was in decent shape from the start, the fresh bearings, seals/gaskets, and clutch kit insured for a solid build.

Ready to rip from trails to roadtrips and everything in between, this old Jeep had a new transmission and the full manual swap to go with it.

Done and done.


Related Content:

AX15 Swap – Jeep XJ Complete Conversion Guide

Jeep AX15 Transmission: Complete Rebuild Photos

2000 Jeep Cherokee Build – DIY Pop Top XJ Camper

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