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AX 15 shifting problem after rebuild


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#1 timmy960

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Posted 09 May 2013 - 10:47 AM

I rebuilt an AX 15 in a 99 Wrangler.  It went back together fine, it shifts tight, only 1 problem.  Shifting from 2nd to 3rd is fine and from 3rd to 4th is good.  I just can't get it to go from 4th to third.  I am guessing it may be a ball or shift plug out of place in the rail or intermediate plate.  Any thoughts?

 

Thanks

 

Tim



#2 Moses Ludel

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Posted 09 May 2013 - 09:20 PM

Hi, Tim...The shift balls, springs or plug theory could be happening, parts out of order; however, before you tear a freshly built unit down, try feeling the detents for each gear.  If the third gear and fourth gear detents make a distinct "click" into place, the detents might be okay...

 

This could be a binding or cocked shift fork or sleeve.  Did you replace brass blocking rings, bearings, and so forth?  Third and fourth gears have a much better engagement on the AX15 than 1st/2nd does.  The shift sleeve for 3rd/4th moves thoroughly over the gear cogs, which the 1st/2nd sleeve does not in some AX15 applications.

 

Is there gear clash?  That would be more symptomatic of plugs out of place or missing, as the shifter would be trying to catch two gears at one time.  3rd/4th is on the same rail and should not cause a sticking problem unless there is cocking or binding, something like the synchro hub springs and keys not indexing properly.  This would allow a key to raise out of its notch in the hub, which is a real possibility with what you're experiencing. Properly positioning the synchro hub springs and keys is essential.

 

Let me know more details, we'll kick this around...Moses



#3 GARYT53

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Posted 18 May 2013 - 04:29 AM

MOSES, I WONDER IF TIM'S SHIFTING PROBLEM  FROM 4TH TO THIRD COULD BE RELATED TO THE CHANGE THAT WAS MADE—LIKE ON THE AX15 I REBUILT. IN MY PHOTOS, SEE THE ANGLED SYNCRO TEETH ONLY ON 3RD GEAR, SLEEVE AND RING.

 

MAYBE TIM REPLACED THE ANGLED TOOTH SYNCRO RING WITH THE STRAIGHT/ARROW CUT VERSION THAT COMES IN A REBUILD KIT? MAYBE THIS CAUSED THE  GEAR AND SYNCHRO RING TO HAVE GOOD BRAKING ACTION, BUT IT IS UNABLE TO MATCH TEETH ENGAGEMENT FROM THE SLEEVE TO GEAR...JUST A THOUGHT...

 

GARYT

 

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#4 Moses Ludel

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Posted 18 May 2013 - 06:54 AM

Gary, welcome to the forums!  Thanks for providing AX15 parts photos...Tim talks about a 3rd gear downshift problem.  Your photos suggest that Aisin may have addressed a downshift to 3rd gear problem.  The angle cut you describe and share in your photos would engage the shift sleeve differently. This would allow easier engagement on the downshift from 4th to 3rd.
 
From a practical standpoint, either ring would work, as they each engage the sleeve troughs accurately (taking a straight-on view).  The difference is that the angled ring teeth would engage the sleeve with a different pressure and slight rotation of the ring.  This is the readily identifiable concern...

 

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 would work if all drivers shifted up and down smoothly—without taxing the synchronizers.  However, American drivers (and other Jeep 4x4 owners) want to affect a quick downshift to 3rd gear.  Another consideration is driving in low range of the transfer case—the 3rd gear downshift problem would be even more exaggerated!
 
If nothing else, this is a testimonial to the detailed design of Aisin transmissions, more like European types than traditional U.S. gear products.  The aim with a wedge ramp instead of arrow-shaped teeth would be the shift “timing” and precise angle of engagement.  This reflects the AX15's overall design quality and close-tolerance fitment.  Aisin and European transmissions are more complex units for a reason...  
 
Does this make sense, considering the parts layout?  As for the tooth spacing and tooth offset on the brass rings, this would keep the synchronizer blocking ring square as it moves onto the gear hub.

 

Great to have you at the forums, Gary!  Looking forward to your sharing...Moses
 



#5 GARYT53

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Posted 18 May 2013 - 04:20 PM

MOSES I THINK IT WOULD BE GOOD TO SHOW THE FULL ENGAGEMENT OF THIRD GEAR AND NOT SO FULL ENGAGEMENT OF FIRST AND SECOND ON THE AX-15 TO SEE IF ANY OTHER BUILDERS HAVE NOTICED OR SEEN THE SAME ISSUE DURING THEIR REBUILD.

 

GARYT



#6 Moses Ludel

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Posted 18 May 2013 - 08:15 PM

Agreed, Gary...See the YouTube video:

 

 

In this video (above), an instructor at Weber State University shares the gear functions of a manual transmission and synchronizers.  For the benefit of AX15 builders, the demonstration unit just happens to be a Toyota version (A150) of the AX15 transmission...As Gary notes, and you all will see within this instructor's 24-minute video, the synchronizer sleeve for 1st/2nd gear does not engage the 1st and 2nd gear cogs as deeply as the 3rd/4th gear synchronizer sleeve engages the 3rd/4th gear cogs during shifts. Although the view is not as clear, the 5th gear sleeve engagement also appears shorter than 3rd or 4th gear.

 

Note: To save time, view the shift sequence and parts alignments from approximately 7:30 to 23:00 minutes.  The entire video is helpful if you want to understand the functions of a synchromesh transmission and how gear speed ratios work...As an automotive technology instructor, I would like to thank Weber State University and the instructor for making this video available as a "public" YouTube download.

 

The unit in this video is a 1992 version.  The unit I step-by-step build at the magazine article is also from the 1990-91 era.  Note the shape of gear cog teeth from that period.  Cog teeth are all arrow shaped, none are the angle shape found on the later 3rd gear in Gary's photos from a 1999 AX15.

 

Our concern here is whether this short sleeve engagement is inadequate for 1st or 2nd gears (possibly 5th, too).  Gary noted the short sleeve throw while rebuilding a 1999 TJ Wrangler AX15 transmission: The 1st/2nd gear shift sleeve does not engage the 1st and 2nd gear cogs to the same degree as the 3rd and 4th gear sleeve engages the 3rd and 4th speed gears.

 

Has anyone else made this observation during an AX15 rebuild?  Both Gary and I question this short throw of the 1st/2nd gear synchronizer sleeve when engaging either 1st or 2nd gear.  Does this lead to trouble?  In particular, can this cause the transmission to jump out of 1st, 2nd or even 5th gear?   

 

Moses



#7 timmy960

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Posted 21 May 2013 - 10:42 AM

Moses

Thanks for your suggestions.  Also thanks to Gary.  I am able to smoothly go through the gears with the engine off.  I think that validates the detents being ok.  I drove it again today and it will not go from 4th to 3rd.  If I slow down to 15 mph and double clutch, it slips in.  I replaced bearings and syncros when I had it apart.  You mentioned hub springs and keys, but would it still shift into 3rd and from 3rd to 4th if that was the issue.  I guess there is something that will not let it slide one way at high speed from the 4th to 3rd (front to back) direction.  I will probably pull it apart in the near future because it is only an annoyance at the present, but it would be nice to have an idea of what needs to be changed to fix it. Could I have reversed the hub?

 

Thanks

 

Tim



#8 GARYT53

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Posted 21 May 2013 - 04:23 PM

MOSES AND TIM...I THINK IT STILL IT HAS SOMETHING TO DO WITH THE MISMATCH WITH THE SYNCRO-RINGS IF IT IS WHAT I BROUGHT UP EARLIER ON THE ANGLED DESIGN MATCH-UP.  GARY



#9 Moses Ludel

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Posted 21 May 2013 - 05:41 PM

Tim, we're each being thoughtful about the AX15. The aim is to make rebuilds perform as new—perhaps better. Gary and I have batted ideas back and forth about improvements to the 1st/2nd synchro and sleeve assembly. 3rd/4th has presented less of an issue, though there is the puzzling Aisin changeover to the angled 3rd gear cog ramps and bronze synchro ring tooth shape...This indicates something inherently challenging about the 3rd gear shift.

You are spot on with your detent analysis if each gear position produces a shift lever feel of "holding" when the lever is in the selected gear position. The 15 mph with a double clutch downshift indicates that the problem is synchronizer related. Essentially, at that road speed and with a double clutch effort, you can synchronize the input and output shaft speeds to the speed of 3rd gear.

As a segue, I once owned a '51 F3 Ford truck with a "spur gear" four-speed transmission (totally non-synchromesh on any gear with rugged straight-cut gear teeth). I taught myself to use the clutch pedal only at complete vehicle stops. Once moving at all, I could shift up or down through every forward speed without depressing the clutch pedal—and without clashing gears. While this may sound unique, it really wasn't.

Older truck and car drivers (well into the 1930s) downshifted straight-cut, non-synchromesh transmissions by either braking the vehicle or accelerating enough in neutral to sync the engine and output shaft speeds for a desired gear's ratio. At the correct vehicle speed, engine speed and output shaft speed, the clutch pedal was dipped, shifter moved to neutral, then the clutch pedal released momentarily in neutral. Only if necessary, the throttle was blipped to change the engine speed slightly to match the output shaft speed for the next gear down. The clutch pedal was dipped again (the "double-clutch" effect), and the driver moved the shifter into the downshift gear before smoothly releasing the clutch pedal.

For a non-synchromesh gear, the trick is to have engine speed match the desired gear speed and the output shaft speed. In good time, you can learn to shift flawlessly and "know" when to affect a shift to each gear—braking and accelerating as necessary to "synchronize" shaft and gear speeds.

Along came synchronizers—for Ford light truck buyers, the solution came with the 1952 introduction of the T98 four-speed transmission. I'm forever grateful for that '51 Ford F3 "learning experience" and have instructed four-wheelers on how to get home from the backcountry with "clutch-less" shifting—like when the clutch mechanical or hydraulic linkage fails...In your case, Tim, you discovered the "sweet spot" for third gear downshifting when the synchronizer proved ineffective.

Your problem is definitely related to the 3rd/4th synchronizer assembly. Unless you have the wrong lubricant in the unit (please share details so we can determine whether that's a factor), the problem will be the hub springs, keys/plates or a thrust washer out of position or missing. In the case of the hub springs, they must be staged properly.

Click here to the magazine page on the AX15 rebuild. Read Illus. AX15-104 to AX15-113 carefully. I describe the alignment of the plates (keys) and springs in detail for both the 1st/2nd and 3rd/4th synchronizers. Throughout the assembly discussion, I outline the direction that the gears and synchronizer hubs face—plus the location of thrusts and critical thrust endplay measurements.

In the Weber State University video, the instructor talks about bronze ring gap measurements as a determinant for ring wear. There is also the issue of placing the correct ring at the correct position. The brass rings in an AX15 can look very similar; however, when placed in the wrong position, the ring will mate with the gear hub incorrectly and not create the needed braking action for "synchronizing" the gear's speed with the hub/shaft.

I am confident that you will find a distinct problem with either the 3rd/4th synchromesh assembly or the 3rd gear/brass ring fit-up. When you do, please share with us, as your comments could be beneficial to others.

Do not hesitate to post questions. The AX15 is not a simple transmission to rebuild. When I decided to share rebuild steps, I knew this unit was complex and took a "textbook" or "blueprint" rebuild strategy. Anyone tackling an AX15 rebuild will be challenged. Everything has to fit correctly and precisely, clearances are critical, and parts alignment is only correct if every single step falls into place properly...

I have been rebuilding manual and automatic transmissions professionally since 1969, methodical and painstaking when rebuilding transmissions with close tolerances. The AX15 is much more a European kind of gearbox than a historical Jeep unit. Tolerances are closer, the cases will only fit with all parts aligned—and that's just the beginning. The AX15 has a steep learning curve...

Moses



#10 Moses Ludel

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Posted 21 May 2013 - 06:58 PM

Postscript on GARYT's comment...If the 3rd gear has one kind of ramp design, and the synchronizer ring has another, this could cause an issue as Gary suggests...Tim, do your remember the design of your AX15's 3rd gear cog teeth: an angled ramp or arrow-shaped?  Do you recall the design of the 3rd gear bronze ring teeth: either angled teeth or arrow-shaped teeth? 

 

Moses



#11 timmy960

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Posted 22 May 2013 - 06:53 AM

Here are the old syncs, and one of the new ones that came in the rebuild kit.

TimAttached File  IMG_0113.JPG   145.57KB   22 downloadsAttached File  IMG_0114.JPG   154.14KB   20 downloads

#12 Moses Ludel

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Posted 22 May 2013 - 10:20 AM

Hi, Tim...There are two photos here, each looks like an original, worn brass ring.  The one at the right shows the plates/keys cutting away at the brass.  The damaged ring was rotating considerably.  What was the condition of the plates/keys at the 3rd/4th gear synchronizer? 

 

The ring at the right has straight "arrow" shaped teeth; the ring at left has offset/angled teeth.  The ring at the right should be 4th gear for your later, 1999 AX15 unit.  Correct?

 

Since I cannot see the new ring (please upload the third photo), I'm not able to determine whether the new bronze ring has straight arrow shaped teeth or offset teeth.  As Gary suggests, on these later AX15 units, 3rd gear has a unique cog tooth arrangement (angled ramp shape, not arrow shaped).  This fits with a unique brass ring design (which has offset crowns on the teeth). 

 

The generic aftermarket rebuild kits apparently do not have offset teeth at the 3rd gear bronze synchro ring.  Aftermarket kits often pattern a specific year(s) design.  The earlier AX15 has arrow-shaped 3rd gear cog teeth and arrow-shaped teeth on the bronze ring—not the offset or ramping design.  Both my magazine rebuild article and the Weber State University video demonstrate an earlier version of the AX15: 1990-92 vintage.

 

This 3rd gear synchro issue came up in JayDLogan's AX15 build, which is also a later Wrangler application.  He and GaryT discovered that Chrysler/Mopar offers a unique part number for the 3rd gear bronze synchro ring plus a unique 3rd speed gear for these later AX15 applications.  (I can furnish Mopar part numbers for the '99 3rd speed gear and the 3rd gear bronze synchro ring if you need these numbers, Tim.)  In this topic's threads, GaryT uploaded photos of the later 3rd gear design found in his '99 TJ Wrangler AX15 rebuild.

 

GaryT, Jason (JayD) Logan and I have each raised questions about the bronze ring for a later AX15 3rd speed gear.  The angled/ramping gear cog teeth may require the offset-point bronze ring teeth like in your photo at left (presumed to be the 3rd gear bronze ring?).  Please clarify which ring fit where in your AX15, Tim.  4th gear appears to be the badly damaged ring at right with straight-arrow shaped teeth.

 

Aftermarket suppliers may need to offer an "early" and "late" rebuild kit—or specific "early" and "later" 3rd gear bronze synchro rings to accommodate the 3rd gear cog/teeth design change.

 

For some solid insight here, I started a brand new thread (click here) on the 3rd/4th synchronizer design change.  Jason Logan (our fellow forum member JayDLogan) and I began an exchange just before these forums launched...I revisited that Q&A and added our exchange as a new thread. 

 

At the new thread, you will find some insightful photos by Jason plus a valuable clue: the later AX15 transmission uses a different 3rd/4th gear synchronizer shift sleeve.  If installed backward, especially with the wrong synchronizer ring match, this sleeve would raise all kinds of trouble with shifts between gears! 

 

Take time to read and review the photos at the new thread, Tim.  Our discussion should resonate...

 

Moses



#13 jaydlogan

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Posted 22 May 2013 - 04:00 PM

Hello guys! I don't know if this helps but it is possible that your synchro rings (blocker rings) for 3rd and 4th are not indexing properly. Meaning that the synchro ring teeth are not meshing with the slider. This can be caused by bad keys and springs. Also, the key slots in the synchs could be worn or not in spec. I got in contact with Aisin with regards to 3rd and 4th synchs. Prior to 1999 the third and fourth synchros where the same, straight cut (house). In 1999, they changed third synchro to an angle cut and fourth synchro to a straight cut. My slider had a angle cut on one side with a corresponding angle cut synchro and on the other side was a straight cut (house) with a corresponding straight cut synchro. The AX15 I have been working on is from a 1999 TJ. If you have an AX15 transmission after 1999, I can give you OEM part numbers for third and fourth synchros Note that Aisin changed the straight cut synchro (house) as well after 1998. There is a slight change in the teeth pattern. Hope this helps!

Jason



#14 jaydlogan

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Posted 22 May 2013 - 04:37 PM

Hey guys! I found that the aftermarket synchros for third and fourth are angled cut and are identical for THIRD gear synchro for 1999 and later. I spoke to Aisin and I was able to get some information. If you opt to use OEM, then for third gear use part number 4897051aa (angle cut) and for fourth use 4897052aa (straight or house). These part numbers match up identical to Aisin specs for 1999 and later. I have done a considerable amount research on this issue and it has been very exhausting. The best thing to do is pay attention to the design of third and fourth and if falls within this variation I have found then these part numbers should be useful. Aisin has told me that prior to 1999 the third and synchros should be identical (straight cut). I have noticed that it is possible that the synchros should be matched up with same cut as the slider. Do not go by the factory OEM part breakdown! Maybe Moses can add to that!

Jason



#15 Moses Ludel

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Posted 23 May 2013 - 09:17 PM

Jason did a thorough job of identifying the features of a late (1999) Aisin AX15 transmission used in the Jeep Wrangler.  Jason, your photos are very detailed and helpful, and I posted them at the new topic I started yesterday, discussing the 3rd-4th gear synchronizer differences.  Click here to see the new topic post and Jason's photos.

 

My two cents worth: If the transmission has never been apart before and shifted normally to this point (aside from wear factors requiring the current rebuild) then match up the synchronizer rings, the sleeve and the gears to exactly the OEM layout.  Do so by taking the transmission apart carefully and laying out all parts in the factory orientation.  Match up original parts and new parts to duplicate the original designs and layout.

 

According to Jason's comments, it sounds like the change year is 1999.  Not surprising that we have a rash of issues, and all of the transmissions in question are 1999 AX15 types.  Apparently, Aisin made the 3rd/4th synchronizer change to solve a shifting issue.  The aftermarket has yet to identify these parts differences, and based on Jason's experience, Mopar had difficulty cataloging them properly.  That would leave only one solution for transmission builders: Match new parts to the OEM design—hunt down parts until they match the original equipment (OEM) design.  Jason's numbers are certainly a place to start.  Like Jason, you need to match what you order and receive to the original parts found in your transmission.

 

     Note: I've not tested whether the use of an earlier 3rd gear and earlier 3rd/4th synchronizer assembly and synchro sleeve will work in these late Aisin gearboxes.  If the earlier parts do fit and work properly, that would be another solution—this has not yet been tested by any of us.  If Jason is correct, and if the parts in his transmission were only used in 1999, there is a problem brewing.  It will become increasingly more difficult to source replacement parts for the late AX15 3rd/4th gear synchronizers used in TJ Wranglers—and likely the XJ Cherokees from the same model year(s).

 

Look closely at GARYT's and Jason's photos.  Gary's photos are within the threads for this topic.  I added Jason's photos at the new post that I started yesterday on the 3rd/4th synchronizer differences: click here.  Open the photos by clicking on each one.  Note the features of Jason and Gary's 1999 transmission parts.  Compare these to the photos in my article on rebuilding the Aisin AX15, Part 1 (disassembly/inspection) and Part 2 (assembly).  In my article, the core transmission is from the early '90s era.

 

Moses




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