AX-15 Transmission Fluid Report

Gary747

Gary747

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Lancaster, CA
I now have about two years on my second AX-15 manual transmission, with about 400K miles on the Jeep. I had problems with the synchronizers not working very well, especially when hot. The gear grinding tendency was bothersome when downshifting, and it was difficult to engage higher gears when accelerating.

I decided that, what the heck... it's only a transmission, so I replaced the 75W90 gear oil with Mopar automatic transmission fluid.

After the first 100 miles to "wash" the thick oil out of the system (synchro rinsing, if you will), I replaced it again with fresh auto-trans oil. One year later, just to examine the oil effects, I again replaced that transmission oil with auto-trans fluid.

Here are the results:

After a year, the drained auto-trans fluid was as bright of red as new. No evidence of degradation.

At the first replacement I noted an immediate improvement to synchronizer meshing. My hard and grinding shift issues went away. Two years later, the transmission still works great.

I park on a concrete surface, and I've no trans fluid leaks on the driveway. The AX-15 seals all seem to be compatible with auto-trans fluid. I check the trans oil level at every engine oil change with no evidence of fluid loss. It stays full, right up to the bottom of the filler hole on the right side.

Cold weather driving is the same as warm weather in terms of transmission operation. It always shifts smooth. Interstate or desert dirt roads all shift easy, either up or down shifting. By the way, I live in the high desert in Southern California, with summer temps exceeding 112° F, and winters down to 17°F

The thinner oil seems to provide plenty of internal lubrication, although I've had no reason to drop the transmission for any maintenance. No unusual sounds or vibration. When the time comes, I will pay close attention to the internal shafts, gears, etc for any indications of heat or lack of lubrication.

My biggest problem is having to explain all this to a shop before they discover the "wrong" oil and replace it with 75W90. Also, some oil change shops won't service the 1990 Jeep with fluids not approved by the manufacturer... even on a 30 year old Jeep.

I would be interested to hear other owner experiences concerning similar oil substitutions. As for me, in the absence of any new problems, I'm going to use automatic transmission fluid in my manual transmission forever more, happily ever after.
 
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To show how little I know about oils I recently found out that Chrysler made a change long ago to the recommended oil for the AX-5 and AX-15 transmission. They say to use 10w30 motor oil instead of the 75w90 gear oil. So I looked into it and found the viscosity between the two is not on the same scale and those weights are actually close to being the same but one is on the gear oil scale and the other is on the motor oil scale.

I have read that ATF will work and in many cases last longer because it's designed for the higher temps of an automatic but never reaches that in a manual trans and still provides good lubrication. I would still change it on the same schedule as the regular fluid but it should last and do a good job.

My only question is will the gaskets and factory RTV sealant hold up. When I rebuilt my AX-5 and put new seals in the NP231 T-case I found that Permatex recommends a specific sealant for the ATF applications where the regular RYV will dissolve. The NP231 T-case uses ATF fluid as a lubricant.
 
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Flyer58 said:
To show how little I know about oils I recently found out that Chrysler made a change long ago to the recommended oil for the AX-5 and AX-15 transmission. They say to use 10w30 motor oil instead of the 75w90 gear oil. So I looked into it and found the viscosity between the two is not on the same scale and those weights are actually close to being the same but one is on the gear oil scale and the other is on the motor oil scale.

I have read that ATF will work and in many cases last longer because it's designed for the higher temps of an automatic but never reaches that in a manual trans and still provides good lubrication. I would still change it on the same schedule as the regular fluid but it should last and do a good job.

My only question is will the gaskets and factory RTV sealant hold up. When I rebuilt my AX-5 and put new seals in the NP231 T-case I found that Permatex recommends a specific sealant for the ATF applications where the regular RYV will dissolve. The NP231 T-case uses ATF fluid as a lubricant.
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Yeah that's been around forever, however I don't follow it. The story is as follows: Aisin-Warner recommends 75W-90 GL3 for the transmission THEY created. Chrysler messes that up and fills them all at the factory with 75W-90 GL5 and prints that in the owner's manual as the fluid to use. Of course that causes problems due to the sulfur in the GL5 fluid. Knowing that, they later came out with the TSB and for some weird reason started telling everyone to use 10W-30. While this works half decently, it is still not the official recommendation by the manufacturer of the transmission. The official fluid to use is 75W-90 GL3, which in modern day has been superseded by GL4 which is basically the same as GL3 ever was which is now extinct. So, really and truly the proper choice is 75W-90 GL4. For that reason, I choose Redline MT-90. I have also tested motor oil and Redline is better. People will argue all day long that "the factory says to use 10W-30", but really that's just Chrysler, the same company to mess this all up to begin with when they filled them all up with the wrong fluid to begin with. It is indeed correct that 10W-30 and 75W-90GL4 are on similar viscosity settings, but GL4 has extra additives meant for gears, bearings, etc, that are not in motor oil. I don't think you'll ever kill the trans with motor oil but it certainly won't shift quite as well. Take that for what it's worth to you. Just thought I'd clear up what a lot of people don't seem to understand.

Long story short, I prefer the transmission manufacturer's recommendation over Chrysler's. What most people miss is that the GL5 was never what the manufacturer told anyone to use to begin with. They start not paying attention to details and mix up GL5 with the proper GL3/4 in their discussions.
 
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Thanks for the 10W30 info... I did NOT know that Chrysler changed that transmission oil recommendation. I do know that I failed (locked up) my first AX-15 using 75W90 and that the heavier oils make the transmission shift harder.

I was concerned about AX-15 seal compatibility with ATF, and spoke a shop owner in the area about it. He had knowledge of numerous Jeep owners with manual transmission who switched to ATF and never complained. I literally decided to risk the transmission to conduct my own trial. There are plenty of AX-15's out there, and if I didn't break something, mine could be overhauled and re-sealed.

That was over two years ago. No leaks, no losses. Just smooth shifting.

Moving on, I recently started a new thread titled "Transfer Case Gearbox Changed" that approaches your NP231 comments, only backwards! Forever, as you mentioned, I used ATF in the transfer case and got 397,000 miles out of it, occasionally adding ATF to top off operational losses. However, my newly purchased (rebuilt) 231J Transfer Gearbox came with the warranty requirement that ONLY 5W30 motor oil be used. You can check that thread for more info, but in this case, the oil swap is backwards... instead of replacing lube oil with ATF, now I'm replacing ATF with lube oil! Again, no leaks. After about 700 miles on the new Transfer Case, I drained and replaced that 5W30 just to flush out any potential manufacturing debris and to check the oil condition. It was perfect.

The only devices that I currently use 75W90 in are the axles, but I've no reason to use anything different in them. They were installed at the factory in 1990 and have endured 398,000 problem free miles. I do change those oils regularly and add the limited-slip additive to the front.
 
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Not knowing any different I went by the service bulletin and put in the 10w-30 motor oil after I rebuilt it with new synchros and bearings. When cold the first shift into 2nd gear seem a little stiff but once I drive about two miles it shifts great the rest of the day. I'm not going to change it but will try the Redline next time around.
 
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machoheadgames said:
Yeah that's been around forever, however I don't follow it. The story is as follows: Aisin-Warner recommends 75W-90 GL3 for the transmission THEY created. Chrysler messes that up and fills them all at the factory with 75W-90 GL5 and prints that in the owner's manual as the fluid to use. Of course that causes problems due to the sulfur in the GL5 fluid. Knowing that, they later came out with the TSB and for some weird reason started telling everyone to use 10W-30. While this works half decently, it is still not the official recommendation by the manufacturer of the transmission. The official fluid to use is 75W-90 GL3, which in modern day has been superseded by GL4 which is basically the same as GL3 ever was which is now extinct. So, really and truly the proper choice is 75W-90 GL4. For that reason, I choose Redline MT-90. I have also tested motor oil and Redline is better. People will argue all day long that "the factory says to use 10W-30", but really that's just Chrysler, the same company to mess this all up to begin with when they filled them all up with the wrong fluid to begin with. It is indeed correct that 10W-30 and 75W-90GL4 are on similar viscosity settings, but GL4 has extra additives meant for gears, bearings, etc, that are not in motor oil. I don't think you'll ever kill the trans with motor oil but it certainly won't shift quite as well. Take that for what it's worth to you. Just thought I'd clear up what a lot of people don't seem to understand.

Long story short, I prefer the transmission manufacturer's recommendation over Chrysler's. What most people miss is that the GL5 was never what the manufacturer told anyone to use to begin with. They start not paying attention to details and mix up GL5 with the proper GL3/4 in their discussions
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machoheadgames said:
I know this is older but people still search for answers and you are giving bad advice 10w-30 full synthetic is recommended by many rebuilders of AX15s as they test this stuff regularly But MT90 is good as well. Royal Purple HPS 10w-30 is literally designed for AX15s per Royal Purple
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Not to argue with the consensus but Ive ran both "gear oil" and motor oil in both 5's and 15's. In cold weather like today @ -1 degrees, shifting with the gear type oils feel painful to the trans and is near impossible. I personally don't care for redlines stuff so I'll pass, so Ive been running 10/30 in the 5 for a few years and it works fine. BTW, places like Jegs or Summit sell G4 gear oil for manuals. Regarding the T case there is some info on Advanced adapters website IIRC that suggests many are having good results with 10/30 in their T cases. My bud had almost 400K on his 01 Ram 4x4 diesel and he tows a 32' 5th wheel across country and has never touched the T case. I figure why mess with what works.
I will mention your comment about shops trying to convince you your wrong. #1, places like jiffy lube are what they are. Pay $150 for a "gold service" and you get what's coming to you. Seriously, I wouldn't let the likes of a quickie lube, peppy boys or the rest touch a lawn mower. Like anything old or high maint from use or abuse, do it yourself and have a first hand understanding of its workings.
 
Gilaguy23 said:
Not to argue with the consensus but Ive ran both "gear oil" and motor oil in both 5's and 15's. In cold weather like today @ -1 degrees, shifting with the gear type oils feel painful to the trans and is near impossible. I personally don't care for redlines stuff so I'll pass, so Ive been running 10/30 in the 5 for a few years and it works fine. BTW, places like Jegs or Summit sell G4 gear oil for manuals. Regarding the T case there is some info on Advanced adapters website IIRC that suggests many are having good results with 10/30 in their T cases. My bud had almost 400K on his 01 Ram 4x4 diesel and he tows a 32' 5th wheel across country and has never touched the T case. I figure why mess with what works.
I will mention your comment about shops trying to convince you your wrong. #1, places like jiffy lube are what they are. Pay $150 for a "gold service" and you get what's coming to you. Seriously, I wouldn't let the likes of a quickie lube, peppy boys or the rest touch a lawn mower. Like anything old or high maint from use or abuse, do it yourself and have a first hand understanding of its workings.
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I completely agree with your "Do It Yourself" advice and did so for years. I found though, as I age, it's not as much fun as it used to be to climb under the Jeep on the driveway! So for basic maintenance items such as oil changes, I farm it out. The local "Grease Monkey" is the business that REFUSED to put my ATF oil selection into my 1990 transmission, nor would they add my "Amsoil Synthetic" brand engine oil. Surprisingly, "JIFFY LUBE" does exactly what I ask. I know they use "affordable" parts and their business model pushes "suggestive" selling, but knowing that, I have no problem saying "No Thank You" to their offer to exchange the coolant, suck oil from the axles, or even air the tires. What they DO do is add my preferred engine oil that I bring in with me, use my NAPA oil filter that I bring in with me, and top off the AX-15 transmission with ATF fluid. In return, I pay them as if they had used their "House Brand of the Day" oil and I pay for their "Lower Quality" oil filter, both of which they can keep. They happily follow my instructions for obtaining my requested oil sample which I send in for laboratory analysis. They drain and bag my used oil filter so I can take it home and cut it open. I even brought in a new oil pan drain plug with a copper seal which they installed without question. Last visit was $52 dollars. I think the secret is to "have courage and be kind". They can tell if you know what you're talking about.

I last updated this thread about 2 years ago, Now I have over 4 years on my AX-15 transmission using only red ATF in the case. No leaks, no noises and it still shifts like new. The transmission checks "full" at each engine oil change.
 
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I understand on the getting older and feel the same. I kinda cringe when its at the point in life I wont, or cant climb under a vehicle to fix it or service it. I built a platform for the ATV's to get them at waist level which is great. As the years tick by I might have to consider a lift in the barn for the vehicles either that or a couple Clydesdales and a big wagon for shopping runs. ;)
 
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Gary747 said:
I completely agree with your "Do It Yourself" advice and did so for years. I found though, as I age, it's not as much fun as it used to be to climb under the Jeep on the driveway! So for basic maintenance items such as oil changes, I farm it out. The local "Grease Monkey" is the business that REFUSED to put my ATF oil selection into my 1990 transmission, nor would they add my "Amsoil Synthetic" brand engine oil. Surprisingly, "JIFFY LUBE" does exactly what I ask. I know they use "affordable" parts and their business model pushes "suggestive" selling, but knowing that, I have no problem saying "No Thank You" to their offer to exchange the coolant, suck oil from the axles, or even air the tires. What they DO do is add my preferred engine oil that I bring in with me, use my NAPA oil filter that I bring in with me, and top off the AX-15 transmission with ATF fluid. In return, I pay them as if they had used their "House Brand of the Day" oil and I pay for their "Lower Quality" oil filter, both of which they can keep. They happily follow my instructions for obtaining my requested oil sample which I send in for laboratory analysis. They drain and bag my used oil filter so I can take it home and cut it open. I even brought in a new oil pan drain plug with a copper seal which they installed without question. Last visit was $52 dollars. I think the secret is to "have courage and be kind". They can tell if you know what you're talking about.

I last updated this thread about 2 years ago, Now I have over 4 years on my AX-15 transmission using only red ATF in the case. No leaks, no noises and it still shifts like new. The transmission checks "full" at each engine oil change.
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You got lucky there are thousands of people on the fb groups complaining about their trans because the wrong fluid damaged it. MT90 or 10w30 is all rebuilders recommend
 
I made the mistake when I first got my Jeep YJ with AX-5 of putting 75w-90 in it and it had such a hard time shifting into first that I changed the fluid after 100 Milesish. After that I had pretty good luck with using Valvoline synchromesh. I did find however that after running it for a while I started getting the symptoms again, but upon checking it on an actual level surface I had overfilled it. Now that it is properly filled it’s been smooth shifting ever since.
 
petey said:
ANY one have a resource for finding transmission fill plugs and gaskets?
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Crown sells them. I always reuse the gaskets and never have had a single problem, in case that’s what you’re concerned about.

83500623 - Fill plug
83500512 - Drain plug
83500513 - Gasket
 
machoheadgames said:
Crown sells them. I always reuse the gaskets and never have had a single problem, in case that’s what you’re concerned about.

83500623 - Fill plug
83500512 - Drain plug
83500513 - Gasket
Click to expand...
I have contacted Crown. They only sell direct to dealers. Contacted 2 dealers, no luck.
 
I run GL4, in mine and shifts like new. GL4 for tractors sold at tractor supply house and omg even wal-mart*, in the huge blue jug. GL4 , 2 gallons
do not use GL5 axle oil.
most stores do not sell GL4 because 99% of cars have no manual boxes, now. yours does.
yes GL3 was upgraded to GL4, and GL3 is not sold now, ever. (unless relic NOS jugs , hah) , and MT1 lube is only for 1959 bus crash boxes ok? (zero synchro)
the rear says API GL4 , and is NO LIE it is.

tractor hydraulic & transmission oil. see rear panel for vast tractors in fact.

If the synco rings are worn out they will grind or balk, I've replaced many in all my cars from 1964 to now, some rings even split, 2nd gear loves to fail in city driving.
not told do all forward gears grind or just 1. does it grind shifting easy too.? (yes downshifting is harder)
the rings inside cones wear out, and go from grooves, to failed glass like flat surfaces.(EOL) the synrcos are designed for only 1 type of lube

My JK has synchos that only work with SYnthetic lube and look alien to me , in my hand. them. (composite syncros, not brass!)
USE ONLY GL4 and win.
The rings do not last for ever, (brass) (<captain obvious sure)
Good luck finding the fix.

the copper gaskets on drain plugs are sold in any size you want, shopping online. MM I.D. matched. the plugs will be hard to match . but diameter is easy to measure in mm, but the pitch is very hard to read on such short distance there.
do not pull the side plugs marked do not remove. or over-tighten any.


do not use GL4 synthetic oil some are so slippery the syncro rings are now hopeless to the max. use Dino GL4 (API grade only)
use a viscosity for you climate matched. or as jeep told you.
 
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I fill mine by volume injected as my tranny has drop plate lower the transmissions. lower. (get the tranny level some way first, just it)
I use a 500ml, injector piston plunger device to shoot my GL4 in. (from right side filler plug)
the whole engine and tranny dips way down from stock. on mine.(pinion angle drop kit) so I jacked up the rear of the car to counter that effect.
GL4 is best, dino grade. works best, synthetic can make syncro fail for way to slippery lube.
the other brands marked synchro-mesh are in fact just GL4 , nothing wrong with those. do not use GL5

one sneaky trick I heat my GL4 in the microwave until warm so it injects way more easy.
wife not at home sure. (grin)
(tactics lots)
 
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Gilaguy23 said:
Not to argue with the consensus but Ive ran both "gear oil" and motor oil in both 5's and 15's. In cold weather like today @ -1 degrees, shifting with the gear type oils feel painful to the trans and is near impossible. I personally don't care for redlines stuff so I'll pass, so Ive been running 10/30 in the 5 for a few years and it works fine. BTW, places like Jegs or Summit sell G4 gear oil for manuals. Regarding the T case there is some info on Advanced adapters website IIRC that suggests many are having good results with 10/30 in their T cases. My bud had almost 400K on his 01 Ram 4x4 diesel and he tows a 32' 5th wheel across country and has never touched the T case. I figure why mess with what works.
I will mention your comment about shops trying to convince you your wrong. #1, places like jiffy lube are what they are. Pay $150 for a "gold service" and you get what's coming to you. Seriously, I wouldn't let the likes of a quickie lube, peppy boys or the rest touch a lawn mower. Like anything old or high maint from use or abuse, do it yourself and have a first hand understanding of its workings.
Click to expand...
"Techs" At a lot of these Jiffy Jim Bob Shade Tree Emporiums are regulated and trained about the same level as Carnies if you get my drift..........

6116894d1d926.image.jpg
 
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