Jeep Enthusiast Forums banner

AX-15 Rebuild Kit

6K views 26 replies 4 participants last post by  Opihi59 
#1 ·
I need to to replace the synchros in my Ax-15 due to grinding in 2nd, 3rd & 4th. This rebuild kit seems like it will do the job:

Rebuild Kit

Has anyone had any experience with it? If so, are the components quality parts?

Also, how do you know when the synchro hub(s) need to be replaced?
 
#3 ·
If you haven't seen Mean Max's writeup on the AX-15 rebuild, it may answer that question. But you'll have to wade through a lot of excellent info to find out.
[URL="http://www.jeepforum.com/forum/f12/major-repair-ax-15-rebuild-1032480/"[/URL]
 
#4 · (Edited)
I read that thread at some point. I recall Southwest Gear in El Paso was recommended somewhere & I called them. They didn't have anything in stock but they suggested Transtar. It seems everybody has Transtar stuff and the eBay part used that part number. Any further input would be great.
 
#6 ·
Not familiar with the Nachi brand, but SKF is top shelf. My three most trusted bearing brands in no particular order are SKF, ***, and Timken.
 
#7 · (Edited)

Attachments

#8 ·
Sort of a dealer's choice. It may be okay with a bushing type pilot if there is enough surface area that the bushing bridges across the scoring, but in long term, the part of the bushing that doesn't wear could embed somewhat into the groove and make it challenging to pull the transmission. Since you have the small snout 0.590" version, you may be able to get this sleeved and finished out to the 0.750" size and go with a different pilot bearing.

Gotta mention though, you have a '93 YJ, and the 93 YJ came with the 0.750 snout rather than the 0.590 snout. There must be some interesting history in your Jeep, since that couldn't be the original transmission in that rig. Tell us more.
 
#9 ·
Gotta mention though, you have a '93 YJ, and the 93 YJ came with the 0.750 snout rather than the 0.590 snout. There must be some interesting history in your Jeep, since that couldn't be the original transmission in that rig. Tell us more.
It started life as a 4-cylinder. The engine and transmission are supposedly from a 1991 Cherokee (block is cast 53008405 4.0L-4 10*18*90).

The input shaft's pilot surface is definately smaller than 0.75". The scoring looks like it is from the cage of a pilot bearing. I didn't yet look to see if it currently has a pilot bushing or bearing; I was just thrilled to get it out last night.

This YJ is set up with an internal slave throwout bearing. Are there other differences in the early/late model transmissions of which I should be aware?

If I buy a new input shaft, should I buy the 0.75" version (if the crank shaft will accept the larger pilot bushing/bearing)?
 
#10 ·
You likely have (had....) a pilot bearing rather than a bushing in yours. A bushing would not be hard enough to chew into that pilot snout in that manner. You'll see it better when you pull off the clutch stuff. A 91 XJ would have had the AX 15 with the small pilot snout, 0.590" so that is consistent with that history. If you were to upsize to 0.750" you would need a different pilot bearing, and may need to remove the larger slug pressed in the rear of the crank that the bearing is then pressed into, but there are differences in front main bearing sizes that may be hard to match up a larger input shaft. The one you linked above is for a T-90 transmission though. Honestly if you do go the route for a new input shaft, it would be cheaper than the costs associated with having a machine shop sleeve your current one.
What would be worth your time and effort would be to convert over to external clutch slave, as you will not find a reliable internal slave unit any more, and if you're going thru the effort to fix your transmission, do something that will help prevent you pulling it out 2-3 X until you happen to succeed in finding an internal slave unit that lasts more than a few months.
Another thought, how is your transfer case sitting? The T-case mount holes on the XJ AX 15 extension housing were drilled 10 degrees (counterclockwise) from how they were drilled for the YJ, so an unaltered XJ transmission would have the Transfer case drooping well down on the driver's side requiring a big hole in the skid plate, or a T-case drop so to speak where your skid plate is lowered at least an inch or so. Take a photo end-on of the back of the transmission, and I'll tell you from that if it's drilled XJ, or YJ configuration.

Start looking for parts to convert to external clutch slave configuration.
 
#11 ·
Quick search on Google and I'm finding repair sleeves that could work for your input snout. A company called Fitzall makes sleeves for a variety of applications. http://www.fitzall.com/KPBD57HD.php I'd give them a call and find out what they have for you. Likely a kit that upsizes your snout somewhat, with a matching pilot bearing, etc. There are other companies that make similar repair sleeve products, or have such items in their product line like Felpro for example. SKF also makes input shaft repair sleeves (Speedi-sleeve), so you can also search about and find out what products they have available for your situation. Also National seal/bearing Redi-sleeve, and I found one on ebay for other applications, but you could also contact them and find out what they may have for you.
 
#12 · (Edited)
Thank you Opihi59. The input shaft is in fact 0.59". Upon further inspection, noting the wear on the input shaft, it appears the damage occurred with a pilot bearing prior to the one I removed. The current pilot bearing was not damaged, but there was lateral slop in the input shaft.

Thanks, I've noted the sleeves as well while searching. I think I'll polish it with fine emery cloth since I believe the needle bearings are largely riding on the smooth surface of the shaft.

This tail housing is also drilled for the YJ transfer case bolt pattern & is clocked correctly.

Surprisingly, the inside looked very clean, with the exception of the expected brass particles. I did note wear on the reverse idler & reverse gear; no chipped teeth. Going into reverse from neutral would grind unless I went to 1st then reverse to slow the counter shaft. Could the grinding simply have occurred due to a worn reverse synchro? Should I file the rough spots on these parts to try smooth them out and/or reshape the gear points, or replace them?

How do you know when to replace the synchro hubs, etc.?

This kit actually has NSK, Nachi, & Koyo bearings. The caged roller bearings are unmarked.
 

Attachments

#13 ·
Good pics. Somebody re-drilled that tail housing to accommodate it being grafted into a YJ, and did a nice job. Must have been a previous Jeepforum member......
There is no reverse synchro in the AX15, to get that you'd need to go to an NV3550 like went in the 2000-2004 TJs but honestly I think the AX15 is better since it is so simple to work on and rebuild. I have the 3550 on the floor in my garage awaiting rebuild; I took it from one of my '04 Rubicons and retrofitted an AX15 I had rebuilt. You just have to get accustomed to waiting for the internals to quit spinning before going into reverse, and going to first is a good technique, then slip gently into reverse. The wear you show on the reverse gears is minimal, not a worry. No need to smooth, etc.
Your synchro hubs will not be worn, I promise they'll be fine, so just put on new synchros. The 3-4 shift sleeve (the part the shift fork moves back and forth) has some very subtle markings around the rim, you must carefully mark which side points forwards, and make sure it goes back together that way. It will go on either way, but will only work under load ONE WAY. Etch it, center punch it in non contact surface, grind X into it w die grinder etc but make sure you mark it before taking apart, you'll thank me later.
 
#15 ·
Have you done Mr B's thing so you can see Photobucket images? If not, it's stickied into the /f176/ forum. I have a step by step tutorial on assembly of the shift rails, interlock plugs and balls, etc in our FAQ section that will require that update to be able to see the images. It should be real helpful in getting the shift rails/interlocks back into the right configuration.
 
#16 · (Edited)
Thanks again, Opihi59. Yes, I have the plugin and your thread will be helpful.

I noticed Mean Max used aviation sealer in his thread here to seal the transmission cases. I know Permatex Ultra Black and Permatex Anaerobic Gasket Maker 51813 are often used too. Which is the best?

Can Permatex Aviation Form-A-Gasket also successfully be used on the NP231 transfer case halves?
 
#17 ·
You know, I really like that permatex aviation sealer, I like to put it around the rim of seals before I drive them in as it acts both as a sealer and lube. I've seen it used in assembling aircraft engines, as a sealer between the block and crankcase after a silk thread is laid down in it--yeah, odd. I've never used it as a sealer though on Transmission or Transfer case housings though. It just somehow to me seems inadequate. I just feel more comfy with stuff like FIPG, like from Toyota, or the Red or Black Permatex RTV stuff.
In restoring vintage metal case chainsaws, such as the old Roper 3.7s that have the fuel tank formed by putting the case halves together, I use Yamabond which is fuel safe, whereas RTV had dissolved in the gas, and leaked. I have not found this necessary to use in transmission or transfer case assembly though, and use the Black or Red RTV without any issues. I've built up a ton of transmissions in the last decade or so, and have had no leaks. Mean Max has also built up a ton as well, and never said he had a problem with Aviation Sealer; I just can't seem to make myself trust it though. Sorry Max, wherever you may now be.

The Ultra black is good stuff, just wear rubber gloves when you put it on as it seems to get everywhere and is a challenge getting it off your fingers, out from under fingernails, and ear holes when you make the mistake of itching your ear hole when you have it on your fingers. Oh, sorry, "external auditory canal," of course.
 
#18 ·
After taking some time away, I'm back at this project...

On assembly, I noticed third gear had strange cupped wear where the bearings ride. The bearings were all flat-spotted as well. Is this a common problem?

The trans worked fine (except grinding on shifts). No strange vibrations were present. The main shaft is fine. Any idea of what could have caused this or if it should have had symptoms associated with it?
 

Attachments

#19 ·
That is the way it is made, it's to allow passage of lube. It isn't wear.

Wait......you referring to the 4 cups on the gear face, or are those thin lines in the bore of the gear what you're referring to. If you're talking about the thin lines where the needle bearings ride in the bore, then that IS abnormal, especially if you are able to "feel" them when you rub your finger across. What does the shaft look like where that gear/needle bearings ride? If it is also worn, both the gear and shaft should be replaced.
 
#21 ·
I concur w getting a new 3rd gear there. Yes, the wear pattern is real strange. I didn't see any heat changes, but how it wore that way as if the needle bearings were embedded into the bore is odd.
 
#23 ·
A new third gear arrived & I got the transmission back together. All in all, as a first transmission rebuild, it was relatively easy (I used this video series ).

The only hang up was it was stuck in reverse. Apparently, the reverse shift rail was pushed forward upon installing the case half or when the shift shaft & lever were reassembled.

The easy fix was to remove the lever & reverse light switch, then push the reverse rod back into proper neutral position. It now bench tests fine by shifting through all the gears...Now onto the T5 & Toploader projects I've had sitting around...But first I'll get this AX-15 back in place to enjoy some wheeling.
 
#24 ·
You'll find some of the older style transmissions more of a challenge. If anything like the Borg-Warners (T10), or Muncie M22s, the shafts are separate from the cluster, and have double rows of little needle bearings front and back, etc.......gotta pack them in with grease and hope you don't dislodge them when sliding the shaft back in. Shift shafts are more simple though since they're external so to speak. I haven't done a T5.

Congrats on the rebuild, they're fun and can be addicting.
 
#26 ·
I put about 100 miles on the rebuilt trans and I've noticed some difficulty down shifting from 3rd to 2nd & 2nd to 1st. All others are smooth. Upshifts are just fine. Prior to the rebuild it was grinding while shifting into all gears but 5th, so I never really downshifted it. At low speed (~10 MPH & roughly 900 RPM; almost stopped) 3rd to 2nd works but not smoothly (4.10 & 31" tires). It takes more effort than it seemingly should. While stopped, engine running and clutch pedal pushed in, it shifts and down shifts through all the gears just fine.

I've not forced the 3 to 2 shift, but when that fails, after putting pressure on 2nd & then trying 1st, it will go into 1st. 2nd to 1st will go, but it requires some effort. Of course, 2nd to 1st goes pretty easy at < 5 MPH.

Is this shifting typical or should I have replaced synchro hubs or shift sleeves too? All bearings, synchros, keys & springs were replaced as well as 3rd gear and the first gear thrust washer.
 
#27 ·
Give it a chance to "bed in" so to speak. The AX 15, and for a fact, a ton of manuals, don't like the 2nd to first downshift unless you are going slowly, or carefully rev match and let it drop in. The 3rd to 2nd will improve. If you used a synthetic lube, it will take a lot longer to bed in, but if you're running 10W30 dinosaur oil it will bed in quicker. Just don't force it, learn to rev match, and it will slowly improve by around 500 miles or so......which is about the time you want to change your break-in oil.

Unless you had some sort of visible wear or damage, there would have been no reason to have replaced synchro hubs or shift sleeves.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top