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AX15: Early and Late Model 3rd/4th Gear Synchronizer Differences


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There has been a long thread of exchanges at Timmy960's topic on harsh shifting after rebuilding an AX15 transmission.  The problem around 3rd/4th gear shift issues has a basis in the redesign of the synchronizer sleeve, bronze blocking rings and the third gear cog teeth for the sleeve engagement.  Jason Logan and I had an exchange about this issue when he rebuilt his '99 TJ Wrangler unit.  That exchange was just prior to the launch of the forums.  For the benefit of all AX15 rebuilders, I am starting a new topic around this issue, beginning with the in-depth Q&A exchange that Jason Logan and I had...Since this exchange, Jason, Gary, Tim and I have been using the new forums to disseminate AX15 transmission rebuilding details...Here is the original exchange with Jason.  I have highlighted important facts:

 

Jason:  Hello Moses!  I have recently taken advantage of your detailed instruction on how to rebuild an AX15 manual transmission.  I am currently working on an AX15 manual transmission from a 1999 jeep tj 4.0L that has never been rebuilt.  I have a question regarding the stock 3rd and 4th synchro ring and the corresponding slider [sleeve]! The stock slider has an angle cut on one side and a straight cut on the other side. Also, the stock 3rd gear synchronizer is angle cut and the 4th synchronizer is straight cut. (I may have these backwards). 

 

Why is it that the dealer and aftermarket only show that both 3rd and 4th synchronizers are identical (either both are an angle cut or both are a straight cut).  I ordered a 3rd and 4th synchronizer from Chrysler and they are identical (straight cut), and when I ordered a set from the aftermarket, the 3rd and 4th were also identical but with an angle cut!  Should I use the Chrysler synchronizers (both straight cut), the aftermarket (both angle cut)  or should I use one of each to replicate the stock setup as described above?  I have put this rebuild on hold for weeks now trying to get some answers from many sources but nothing has been rock solid.  I was hoping you could help me and give me some clarification on what is the best set up and why?  Why does the slider [sleeve] have different cuts?  Why do the replacement synchros have different cuts, different part numbers and configuration of teeth? Thanks for any information you can give me. 

 

Jason Logan

 

post-1-0-24420400-1369259567_thumb.jpgpost-1-0-21811600-1369259569_thumb.jpg post-1-0-22514200-1369259571_thumb.jpgpost-1-0-56677000-1369259572_thumb.jpg post-1-0-90331100-1369259573_thumb.jpgpost-1-0-40956000-1369259575_thumb.jpg post-1-0-06700100-1369259589_thumb.jpgpost-1-0-90363000-1369259591_thumb.jpg

These photos courtesy of Jason Logan ("JayDLogan"), forum member...Note the 3rd/4th gear sleeve and cog design for his 1999 TJ Wrangler AX15 transmission. Click on each photo to enlarge image.

 

 

Moses: Jason, I would match synchronizers precisely to the originals and in their original locations.  Measure the diameters of the rings, their angles and, most importantly, their fit against the synchronizer hubs in their correct positions. Make sure you face the synchronizer sleeve in the correct direction.

 

Start with the original rings in correct relationship to the synchro hubs and sleeves.  Note the overall “width” of the synchronizer assemblies, and then compare this with the aftermarket (new) synchros from both generic and Chrysler sources. 

 

The goal is to have synchro rings that will behave and fit just like the originals.  Wear on the OEM rings is typically slight, perhaps a few thousandths, so you will know immediately if the parts are either wrong or in the wrong locations. 

 

AX15 synchro rings are not the same diameter, and the difference is slight, often confusing the assembly.  My article provides details on the kind of “fit” and end plays you should achieve during assembly. 

 

Take your time, Jason, you’re already ahead of the game by questioning the parts to make sure of their fit and placement.  The OEM layout and fit is your template.  Match this and you will “restore” that AX15!

 

Trust this helps…I’ll be at Moab through Thursday and out of communication.  Let me know your findings in an Email.  I will answer next Friday…Best of luck, I know you will do the right thing here…

 

Moses

 

Jason:  Thank you very much for all of your information and help - my dilemma is - when I have ordered the synchro rings from Chrysler (they sent me 2 identical 'straight cut' synchro rings) and when i ordered from the aftermarket (they have sent me 2 identical 'angle cut' rings) but my original synchro rings have 'one of each' cut (one ring is a straight cut and the other ring is an angle cut).  Although all synchro rings ordered are the same diameter, angles and fitment as my originals,  I'm not sure if I should be using what Chrysler sent me (the 2 straight cut rings) or what the Aftermarket sent me (2 angle cut rings) - or should I be using one of each cut to match identically up to the original set up?   I would have thought Chrysler would have sent me one of each (angle and straight cut synchro ring) based on the fact that my original rings are 'one of each' cut.  And my second dilemma is - the number of teeth and location of the teeth on each ring ordered are not set up identically to my original configuration of teeth on my original rings - does that matter?  I'm extremely grateful for your reply and value your expertise.  Jason Logan   

 

Jason added these parts details: I found some other information, Moses!  If you look at earlier years of the Jeep Wrangler 1997-1998 they have used part number 4897051AA (for both 3 & 4 synchro) or 4897052AA (for both 3&4) depending on the month the jeep was made.  Part number 4897051AA is a synchro ring that has teeth that are angle cut and part number 4897052AA has teeth that are straight cut (shaped like a house). The jeep I am working on is a 1999 that calls for part number 4897052AA for both 3 and 4.   It looks like at the factory, they have put part number 4897052AA for synchro 4 (near the input shaft) and 4897051AA for synchro 3 (near third gear).  Very confusing!  I also found, like I noted before in my second email, that the teeth of part number 4897052AA and 4897051AA are in a different configuration around the ring slightly than the originals as you can see in the pictures.  I have purchased many 3 and 4 synchro rings but none of the teeth patterns match up!  I had no problems matching up 1,2 and 5 synchros.  I hope this helps you understand what I am up against!  Thanks again!  Jason Logan  
 
P.S   I purchased part number 4897051AA today from Chrysler to clarify if it was angle cut and indeed it was! 

 

Moses: Hi, Jason, I’m just back from Moab, UT Jeep Safari…You sent great photos, this is all very interesting!  Since the gear/ring in question is really 3rd gear, my belief is that Chrysler/Aisin discovered downshifting to 3rd problems and implemented a remedy.  The angle cut would engage the shift sleeve differently, apparently allowing easier engagement on the downshift from 4th to 3rd.

 

It would seem like either ring would work, as they each engage the sleeve troughs accurately (taking a straight-on view).  The difference is that the angled ring would engage the sleeve with a different pressure and slight rotation of the ring.  Just a guess, but this seems the only identifiable issue.  Think about the third gear engagement: 

 

Shifting up, there is the lag in the shifter’s neutral gate and a “slower” engagement of 3rd gear.  Shifting down, however, would be a direct, quick movement of the shift level and fork.  Consequently, the sleeve would want to quickly rush over the brass ring teeth—without providing smooth or effective braking action at the gear hub.  This would cause harsher gear engagement.  Apparently, the slight angle makes the downshift to 3rd gear smoother, with better braking action and less risk of gear clash. 

 

Probably, either design would work if all drivers shifted up and down smoothly and without taxing the synchros.  However, American drivers (and others with Jeep vehicles) want to affect a quick downshift to 3rd gear.  The concern here, though, is to match the bronze rings with the updated synchronizer sleeve design.

 

Does this make sense, considering the parts layout?  The tooth spacing and offset on the rings has more to do with keeping the ring as close to square as it moves onto the gear hub. 

 

If nothing else, this is a testimonial to the precision design of Aisin transmissions, more like Euro types than U.S. gear products.  The aim with a wedge ramp instead of arrow teeth is the shift “timing”, and that’s a precise consideration.  This reflects the rest of the AX15 design quality and fitment.  These are more complex units for a reason.

 

I’m sure your build will be stellar, Jason!  Let me know how this turns out.

 

Regards,

 

Moses

 

Jason: Makes perfect sense Moses!  Would it make sense to you to use the angle cut synchros for both sides of the slider even though the slider on one side is straight cut and the other is angle cut?  I am still unsure if I should use both angle cut synchros, both straight cut synchros, or use one of each. The rebuild kit I purchased had two angle cut synchros, I am wondering if this is the upgrade? To me it is like rolling the dice on this decision!  Thanks for all your input.  Very much appreciated.
 
Regards,
 
Jason

 

post-1-0-24420400-1369259567_thumb.jpgpost-1-0-21811600-1369259569_thumb.jpg post-1-0-22514200-1369259571_thumb.jpgpost-1-0-56677000-1369259572_thumb.jpg post-1-0-90331100-1369259573_thumb.jpgpost-1-0-40956000-1369259575_thumb.jpg post-1-0-06700100-1369259589_thumb.jpgpost-1-0-90363000-1369259591_thumb.jpg post-1-0-15265300-1369259859_thumb.jpgpost-1-0-30743800-1369259862_thumb.jpgpost-1-0-88721900-1369259863_thumb.jpgpost-1-0-75657900-1369259865_thumb.jpgpost-1-0-51804400-1369259887_thumb.jpgpost-1-0-98982600-1369260307_thumb.jpg

Photos courtesy of forum member Jason Logan...Note the OEM synchronizer design for this late version of the AX15—Mopar parts.

 

Moses: I would follow the OEM approach if you’re sure the transmission is original, never before apart (which you believed from the start).  The model year is late enough in the game for the synchro "solutions" to be in place…I would match the bronze rings and synchro sleeve carefully to the OEM layout. If this transmission shifted well for all of those miles, I would take this approach!

 

As a final check, place the new synchro rings against the gear hubs to be sure the fit is aligned.  You can put a light film of grease on the ring contact surface to read the fit.  Wipe the grease away before assembly and coat the ring with a thin film of gear lube.

 

Let me know how this all turns out, Jason…

 

Best,

 

Moses

 

Jason: Thanks again Moses!  I hope you had a successful trip to Moab,  UT Jeep Safari.   I have wanted to go for many years.  Wish me luck on the AX15! 
 
Regards

Jason

 

Moses: Hi, Jason…Moab is breathtaking scenery, with contrast ranging from sandstone/slick rock to alpine peaks capped with snow this time of year, the Colorado River, arches and formations, all of it! I trust you’ll make it at some point, and if so, let me know.  I do make the Moab Jeep Safari each year…Like Canada, we live at a “winter zone”, 4400 feet elevation near Reno.  We look forward to winter’s end, and Moab Jeep Safari has become our annual end of winter/early spring gathering!

 

You’re going to do a great job on this AX15!  Follow the assembly steps faithfully, there are no shortcuts.  When completed, you’ll have a smooth-shifting unit, as new, and that will be very gratifying!  Let me know the outcome…

 

I launched a message board today with a large number of forums at www.4WDmechanix.com/forums.  It would be great to see your involvement if you have the time.  Tech forums need detail-oriented members!  It’s new, and I’d value your feedback about the forums you find interesting, the sign-up procedure, member validation and use.

 

Best,

 

Moses

 

Note...Jason and I moved this conversation to the new forums at this point...When rebuilding an AX15 that has never been rebuilt before, lay out the parts as you take the unit apart, identify the synchronizer design for 3rd/4th gear, and match parts to the original design. There is a distinct difference between "earlier" AX15 and "late" AX15.  The rebuild core in my magazine article and the A150 (Toyota version of the AX15) depicted at the Weber State University YouTube video (click for post topic threads containing the embedded video) are 1990-92 "early" AX15 design.  Later model Jeep vehicles with the AX15 use a redesigned 3rd/4th synchronizer assembly...Rebuild accordingly, matching and using the right parts! 

 

Jason has added charts from an Aisin direct dealer that show the synchronizer applications for 1998-99 AX15 transmissions.  Make sure you check your synchronizer rings and the synchro sleeve design for 3rd/4th gear.  Install matching rings for your transmission.  Be certain to install the synchro sleeve in the correct direction!  ("House" or arrow shaped points match the 4th gear ring with house or arrow point teeth.) Here is an approximate application list with Aisin part numbers (not Jeep/Mopar):

 

post-1-0-62834500-1369407655_thumb.jpg

Click on image to enlarge...Thanks to Jason Logan for the chart!

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  • 8 months later...

Great info.  I am in the process of rebuilding my AX15.  It has been a slow project as I don't have much time at any one moment to spend on it.  Before I ordered my rebuild kit I emailed the supplier and he informed me that all the kits he sells have the updated style synchros.  He stated they don't make the old style any longer.  My kit arrived and they are correct :)  Bummer part is I chipped away a few corners on my second gear while attempting to press it off.  I guess I'll be sourcing a new/used second gear. 

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If you can find a very original (in premium shape) 2nd gear used, that could be helpful.  Good gears are out there, this is a constant mesh gear, so the wear points would be the endplay thrust face and the synchro hub engagement teeth on the gear.  Unless the synchronizer was severely worn or abused, the 2nd speed gear will be intact.  A new second speed gear could be costly, hunt for a used one first...

 

Keep us posted, TTippetts, we're here to help with your AX15 transmission!

 

Moses

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  • 7 months later...

Moses, great site. I appreciate the effort and the How-to. My question is the same as above, but what I am getting from the discussion is that I should use what came with the transmission, assuming it was never rebuilt. My friend has a 96 Cherokee with the AX15, when he asked me to rebuild it I thought no worries, but when I got the rebuild kit from him there were indeed two rings with a single 45 degree cut in them versus the two 45 degree cuts that make a point which were what came out of the transmission. So should I install the old ones if they are in good condition or should I install the after market, single angle cut rings?

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Tim, my approach with synchronizer parts is a direct match.  What does not work is "mix and match" of various parts or designs.  If the original brass blocking rings, sleeves and hubs are still in good condition, with the braking ridges on the inside of synchros still capable of grabbing the gear hubs securely, I would reuse these parts. 

 

Measure the synchro ring to hub gaps or movement with parts in position on the shafts.  This is a clue about wear at the brass ring braking surfaces.  If these specs are within tolerance and the gaps are good, you should have no issues with these parts.  Correct gear lube is the other concern with synchronizer performance.  The right lube will allow smooth shifts and also permit the brass rings to "brake" against the gear hubs.

 

I am in the process of producing a narrated how-to HD video on the AX15 transmission rebuild.  It will be a feature at Vimeo On Demand shortly.  Watch for the release...

 

Moses

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Thank you for the reply, will do. Now I need to just hunt down the correct snap rings. So far a few common trends:

 

1. Companies list them in stock and they are in fact not, extremely aggravating to get the "we don't have those in stock, even though our page said specifically we do". I under stand their side of it. 

2. Omnix had there own part numbers on top of the FSM part numbers, a shame because even when listed it only tells you the thickness and not the application (1-2, 5th, input, etc.)

 

It's coming though. I'm rebuilding the 4.0 as well so I just hop around as parts come in. 

 

I look forward to the videos, although I have to say the pictorial how-to was amazing and allowed me to have a few beers and still keep on task if you know what I mean (no thinking ;))

 

I will, if I may suggest the following. My only one issues is orientation of some things. As in they could potentially get installed incorrectly like the hubs (which I figured out was pressed on from the chamfered side) and the sleeves. Those were my only points were I had to really think before I did. Other than that it was a well written and photo documented piece, much appreciation. 

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Thanks, Tim...I'll keep in mind your suggestions when I do the video.  By habit, I lay pieces out in order of disassembly and am oriented before parts cleaning.  Others may lose track, though, and you make a good point.

 

Keep us posted on how this works out for the XJ Cherokee project.  Also where you find the snap rings you need.  Keep in mind that they are selective fit thicknesses.

 

Moses

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  • 2 weeks later...
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Tim, thanks for the update on snap rings...Please keep us posted on your project.  

 

Last night, I phased out the AX15 article at the magazine.  The day before, I uploaded a 94-minute narrated HD video to Vimeo on DemandThe video is now a streaming rental.  Here is the trailer for that video:

 

 

During the frame-by-frame video edit, I kept your comments in mind, making clear the direction of orientation for each and every component.  Using verbal instructions with large, ultra sharp images and zoom focus is much easier to follow.  In the audio tracks, the parts descriptions and layout unfold while the viewer continues the hands-on work.  Audio-visual instructions simplify the entire process

 

I am pleased with the monumental amount of traffic that benefited from the two-part AX15 article over the past four years.  Over 80,000 viewers found their way to this material.  The 94-minute HD video offers even more detail. 

 

Vimeo apps enable viewing on everything from a cell phone or tablet to a laptop, PC or even a big screen HD television.  I did the final pass on a 40-inch HD screen, and the color and shading are vivid.  Visualize the images you worked with on the "page" of the article.  Imagine that same caliber of artwork on a big screen.

 

Thanks for your comments, Tim.  Looking forward to your continued involvement at the forums!

 

Moses

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  • 5 weeks later...

Took a break from my buddy's build after all, my Jeep is good to go ;).  I also spent some time upgrading my Raptor 700 for weekends where I want to go fast and have just completed college finals but now I am back at it.

 

Transmission is being put together as I type this. Front plate just went on, waiting for it to settle and I plan on backing off the torques then torquing in back down. Then I just have the rear/extension housing to throw on, exterior components, detents and shift arm shaft and it should be good to go. As for your video I am sure its very well put together if it even has a tenth of the effort you put into the written how-to.

 

It's been so long since I have messed with transmissions, and being my buddy's rig (didn't want to let him down and wanted to save him a buck or two as we are doing a full ground up rebuilt, Dana 60s, Atlas, engine and tranny rebuild, 3/4 link long arm, exo cage, etc.) I relied heavily on your how-to to ensure success and I thank you.

 

I will contribute and check in often to help other off roader's who need help. I'll be on here more often as I need the garage space to rebuild an arcade machine so I want his rig done ASAP! lol. 

 

 

Tim

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Very pleased to get your update, Tim...Glad you're past finals and the buddy build!  Looking forward to your participation and some insights into your Raptor 700 at the ATV/UTV forum.  Know you'll have a significant contribution to make there, and the segment could use your input and enthusiasm! 

 

Moses

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  • 4 weeks later...

Things have changed here recently. My buddy and I are moving to Nevada so I have been a bit busy lately. I think I already know the answer to this but the rebuild kit (AX15) came with extra seals that just seem to go nowhere. Keep in mind, I followed your guide so the leftovers were not pictured or talked about. One is a stepped seal (by outer diameter), one is a stepped seal that seems to be two pieces glued together (one black one blue) and the other is a metal sleeve with what I assume are oil grooves machined inside the inner diameter of it and it has one single hole drilled through the sleeve. I have no idea why they added these to the kit. Any input on this Moses? By the way, I just noticed you live in the Reno area. We are moving to the Fernley area (work at NAS Fallon). 

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Tim...Sounds like the kit includes parts for a RWD two-wheel drive Aisin AX15 version as well.  This would include the tailhousing or rear driveline slip yoke bushing and slip yoke seal.  The other seal could also be 2WD version related.  If you accounted for each of the parts in the AX15 article (now a narrated motion video rental at Vimeo On Demand), you should be home free!  Think of it, there were 2WD XJ Cherokee 4.0L models that use the 2WD/RWD version, also similar applications in GM Isuzu pickups and Toyota trucks.

 

Guess what...We'll be neighbors soon!  The magazine base is Fernley, 30 miles from Fallon.   If you're setting up at Fernley, watch for the '99 XJ Cherokee with the 6-inch long arm lift and Warn insignias at the rear quarter panels or the magazine's red Ram 3500 4x4 with signage.  Or maybe you'll spot me scorching across remote desert or minding the speed limits (highly recommended) on the Fallon Highway (50-E) with the Honda XR650R.  (Even the Honda XR350R can kick up respectable dust in the desert!)...We'll grab a cup of coffee and discuss AX15 transmissions till we're blue in the face!

 

Have a safe, productive move.  Welcome to the neighborhood, you'll like the greater Reno/Lake Tahoe Area and soon discover the Black Rock Desert and High Rock Canyon!

 

Moses

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Thanks for the reply, I figured as much. I wasn't the one who took the tranny apart so it just hovered over my head. 

 

Engine is almost done, we need to drop it in to get the right placement of the support that came with his long arm kit, in which we can then start tack welding in some of the control arm mounts and get the Currie Rock Jocks in so we can at least roll her up on a trailer to transport to Fernley where we can finish the build. 

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Exciting project, Tim!  Tow it safely to Fernley...We're on the map for parts and such, Reno/Sparks has a 4-Wheel Parts outlet, Summit Racing's western distribution warehouse is at Sparks with a retail component...Fernley just opened a Big R ranch supply that has a really good supply of everything you'll need to get through a Sunday project with your rolling stock, including hardware, welding, tool needs, electrical, air supply and Carhartt work clothes...See ya round town soon!

 

Moses

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  • 6 years later...

Hello Moses,

I'm rebuilding the AX15 from a 99 TJ and I've exactly the same issue than Jason : 3rd & 4th synchro are different. Do you know where can I buy the 3rd synchro ring with assymmetric teeth (my rebuild kit comes with symmetric teeth only) ? 

Thanks.

Jeremy

 

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Hi, Jeremy...Jason's comments came with part numbers.  (See copy-and-paste quote below.)  I did a quick search and came up with these two links.  The 4897051AA is readily available from Mopar still.  The 4897052AA is shown as "No longer available".  I did find that number from ZM Jeep (much lower price, too).  Not knowing that source, I suggest you call to confirm whether they have this part and maybe the other synchro ring as well.  The price is much less costly, and you can share both rings' features to confirm whether they have the one(s) you need.  There is also a possibility that Crown would have one or both of these rings.  Try them as well.

https://www.moparwholesaleparts.com/oem-parts/mopar-ring-synchronizer-4897051aa

http://stores.zmjeeps.com/blocking-ring-4897052aa/

You can also try eBay for NOS parts, they come up there, it's a matter of timing.  You can also check with a Jeep dealership to confirm whether the 4897052AA has a superseded part number.   If there is a superseded part, see whether you must also purchase a matching synchro sleeve and/or hub for that type synchronizer ring.  Determine whether the superseded ring fits with no other changes.    

"Jason added these parts details: I found some other information, Moses!  If you look at earlier years of the Jeep Wrangler 1997-1998 they have used part number 4897051AA (for both 3 & 4 synchro) or 4897052AA (for both 3&4) depending on the month the jeep was made.  Part number 4897051AA is a synchro ring that has teeth that are angle cut and part number 4897052AA has teeth that are straight cut (shaped like a house). The jeep I am working on is a 1999 that calls for part number 4897052AA for both 3 and 4.   It looks like at the factory, they have put part number 4897052AA for synchro 4 (near the input shaft) and 4897051AA for synchro 3 (near third gear).  Very confusing!  I also found, like I noted before in my second email, that the teeth of part number 4897052AA and 4897051AA are in a different configuration around the ring slightly than the originals as you can see in the pictures.  I have purchased many 3 and 4 synchro rings but none of the teeth patterns match up!  I had no problems matching up 1,2 and 5 synchros.  I hope this helps you understand what I am up against!  Thanks again!  Jason Logan"

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