Swapping my old AX15 for a new one

Pravius

Pravius

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Detroit, MI
Currently in analysis paralysis trying to figure out a sane order of operations from both a logical and also a financial perspective on a light resto I am doing.

Just picked up a 1999 Sahara, only 83K miles currently, mostly all original, 2.5'' (I think) sky jacker lift. Bought it knowing it needed some work done. Gasket was blown and oil was leaking down the passenger side, 33'' tires were rubbing so added some wheel spacers, fluids flushed (incl diff inspection and fluid change).

My AX15 has been acting a little strange, very hard to get into 1st and 2nd if I am in a higher gear and need to downshift, almost impossible to go from 3rd to 2nd or 1st if I am moving, becomes much easier if I am not in motion. Have also had some minor issues getting into first from red lights intermittently. After taking it to the shop, local mechanic used Syncromesh to see if that helped at all. It seemed to help a little but I think it's possible the synchros are starting to go. Shifting into 3rd, 4th, 5th is fine and no issues, so I don't think it's clutch related and there has been very little to no grinding. Looking at a complete replacement with a new AX15 from Novak or Advanced Adaptors.

I plan to keep this Jeep for a long time, using it mainly as a toy but sometimes as a driver, my wife and I share a lease, we both work from home. I may even give this to my daughter when she is old enough to drive, 13 years or so away, lol. I am pretty OCD and like to make sure my vehicles are in very good working order.

The remaining items I would like to do on the Jeep:

- Wheels and tires
- Paint (Need touch up's, minor scratches / dings, some big chucks down to bare metal on grill from a winch that did not fit the stock bumper.
- Replace front end / re-do lift / replace front and back shocks (its working, steering is a little loose but this may be normal, weird sounds sometimes when turning. I have no idea when this was done last, parts appear to be a bit worn.
- Trans Swap / Clutch replacement with new Flywheel.

Obviously, this is going to get expensive. I can do and have done quite a bit of minor stuff mostly cosmetic but all of this I would leave to a professional.

What is your opinion on the order in which this should be done or prioritized. Just looking to get some opinions and wisdom from your past experiences.
 
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The first thing I noticed when I purchased my 97, was the shifting in the AX15. It was just as you described above. I got several suggestions to change out the fluid, and put in Red Line MT-90. Between that and just getting used to the shifting, I haven't had issues with the transmission. Its worth a shot. AX15 is a pretty good transmission.

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DaYooperTransplant said:
The first thing I noticed when I purchased my 97, was the shifting in the AX15. It was just as you described above. I got several suggestions to change out the fluid, and put in Red Line MT-90. Between that and just getting used to the shifting, I haven't had issues with the transmission. Its worth a shot. AX15 is a pretty good transmission.

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I have been reading a lot about MT90 on the forums for the AX15. Thanks for suggesting this, I am going to drain out the syncromesh and fill with this to see if there are improvements before committing to a new AX15.

Do you know the typical mileage you can get out of an AX15? I have read some have as high as 200K+ on these transmissions which makes me think at 80K replacement is kind of nuts.
 
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I'm doing the exact thing you describe. My 1998 Sahara has 160k on it, and while the AX-15 still shifts decent, you can tell that it has worn synchros, and 1st is a bit tough on a cold day. Part of this is from the PO running the wrong fluid in it, as the AX-15 needs GL-4 for the brass synchros. My Jeep needs a clutch, so I have the Luk clutch kit, a new flywheel, and a new AX-15 from Novak waiting to go in when time allows.

With that said, at 80k miles I doubt your trans is worn, and the Redline MT-90 improved the shifting in mine by a lot, even after it had the wrong fluid in it for however many years before my ownership.
 
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jeepguy03 said:
I'm doing the exact thing you describe. My 1998 Sahara has 160k on it, and while the AX-15 still shifts decent, you can tell that it has worn synchros, and 1st is a bit tough on a cold day. Part of this is from the PO running the wrong fluid in it, as the AX-15 needs GL-4 for the brass synchros. My Jeep needs a clutch, so I have the Luk clutch kit, a new flywheel, and a new AX-15 from Novak waiting to go in when time allows.

With that said, at 80k miles I doubt your trans is worn, and the Redline MT-90 improved the shifting in mine by a lot, even after it had the wrong fluid in it for however many years before my ownership.
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Thanks for this. It's possible I may need a new clutch assembly as well (this could be as simple as the throwout bearing or something dumb like that). I just keep thinking, if I am going to keep it forever and replace the clutch, might as well spend the money on a new trans while it's out for clutch replacement for piece of mind (and to save on labor) and keep the one I have as a spare just incase. In reality though, it's about $2.6k for trans/core/clutch/install labor.... that is where I go into analysis paralysis considering all of the other things I want to do. I have the money, do I want to spend it, no, but I will if it ensures I have a solid Jeep for the next 15+ years or so.
 
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JKP said:
Jeep and Aisin now recommend you run syn 10w-30 in the AX-15 if you can't get GL4 lube. So if you want to do a cheap flush of the trans, this is a lot cheaper than using MT90.
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Chrysler recommended 10W30 after they incorrectly filled with and recommended GL5 to from the start of using the AX15 in 1989. Aisin Warner still recommends 75W90 GL3/4 as they have all along.
 
I bought my ‘97 with an AX-15 at 150K and it had pretty much what OP describes going on. The rec redline fluid improved it a lot, though still notchy 1-2, and 2-3, especially when cold. I’ve daily driven it for 10k mi and it’s no worse. Although I may get the Novak unit someday (if things get worse), my bet is it’s fine for a while and the $ could be better spent.
 
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My AX15 has 206K and I bought my 1999 new. I ve changed gear lube every 60k and shifts great. I m using RL MTL rather than MT as my research showed it helped more especially in cold weather.

It’s not cheap but I d drain it and give the MTL a try. Unless the PO /s abused that AX15 it should have lots of life left!!
 
Had my AX-15 since new from Rockland Standard Gear in NY. And 2nd gear has always been a little difficult to get into. But inconsistently. Sometimes easy, sometimes not. Less notchy and smooth, Ive noticed, when going up a hill and shifting into 2nd.

Ran great w Pennzoil synchromesh, but not as awesome with the Redline everyone recomments. So damn odd, but true. Even getting slightly notchy in 3rd now. That said, Im planning on going back to Pennzoil.

OP, I don't think your trans in ready to be dumped yet. The AX-15 is basically a truck tranny, if Im not mistaken. Its a rugged, durable trans. Someone correct me if they opine differently or can school me.
 
I had a clutch go out in my YJ (actually, it was the throwout bearing) in my AX15. When I drained the tranny fluid, not much came out :( It was always pretty whiney...it had about 200k miles when this happened

I replaced the clutch with a Luk, filled the transmission with 10w30 for a few miles, then MT-90. It still whined in every gear but 4th. The local transmission shop said 4th gear uses none of the other gears, it's a straight shot to the output shaft...hence, no noise. All my other syncros were gone.

Bought a rebuilt AX15 for $950 two years ago, been happy with it. The Luk clutch kit is great, and I replaced the flywheel too. I believe it was less than $200 for the clutch and flywheel. I would imagine you could run an AX15 into the ground...they are pretty solid. Kinda a perfect match for the inline 6 cylinder 4.0
 
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Thanks to everyone for the opinions. I am going to spend my time and money focusing on my suspension right now and this weekend I will drain out the synchromesh and put in RLMT90 to see if I notice any improvements. I have no grinding at all currently, I drove it a bit yesterday paying close attention to shifting and noises and my biggest issue right now is downshifting from 3rd or 4th to 1st, it's impossible to get it into first from those gears if I am moving, when I try I hear a slight whine from the trans the harder I push the louder the whine.

I only ran into one issue yesterday as I was approaching a red light in fourth gear, I started to slow, the light turned green. My speed dropped down to about 10 mph, put it in neutral, tried to get into first at 10mph, no dice so went to second and was able to get around it. Chances are it's not likely for me to have to go from 4th or 3rd to first often and if I need to, I can try to use 2nd. If I am completely stopped, everything seems to work just fine, way better after the synchromesh was added and can only imagine RLMT90 will slightly improve it even more.
 
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I can slide into first when Im slowing down but rarely do I do it, and only when Im creeping to a halt. From what Ive been told, it's not good practice to downshift. Guess it depends who you talk to, but this was explained to me by someone at Rockland Standard Gear.
 
fourpointzero said:
I can slide into first when Im slowing down but rarely do I do it, and only when Im creeping to a halt. From what Ive been told, it's not good practice to downshift. Guess it depends who you talk to, but this was explained to me by someone at Rockland Standard Gear.
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I'm not sure what the "proper" way is to drive a manual, but I've driven several over the years and never downshift while coming to a stop, that's what brakes are for. I've driven everything from tractors, farm trucks, Jeeps, BMWs, etc. I only downshift to help slow down on a hill with a loaded farm truck, but that's kind of a different scenario. I wouldn't do it with an AX-15, it's easier just to put it in neutral and coast while using the brakes.

Who knows, I'm sure I've been doing it wrong this whole time lol.
 
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I very well could be using the wrong terminology. Typically when coming to a stop I always pop it into neutral and use the brakes to stop, I typically do not "downshift" to slow. Just for clarification for anyone who may read this thread down the road, I am mainly talking about scenarios where I am slowing down for a red light (or something else), pop into N, but then say the light turns green and I have to accelerate again.

So in essence say I was in 4th (45MPH) —> Neutral (Brakes to slow) —> Light turns green (going about 15-20MPH)... it's only then I cannot get it into gear which is why I believe it could be synchro related.
 
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Pravius said:
I very well could be using the wrong terminology. Typically when coming to a stop I always pop it into neutral and use the brakes to stop, I typically do not "downshift" to slow. Just for clarification for anyone who may read this thread down the road, I am mainly talking about scenarios where I am slowing down for a red light (or something else), pop into N, but then say the light turns green and I have to accelerate again.

So in essence say I was in 4th (45MPH) —> Neutral (Brakes to slow) —> Light turns green (going about 15-20MPH)... it's only then I cannot get it into gear which is why I believe it could be synchro related.
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In those situations I usually just go right for 2nd, but I also have 3.73 gears and 31s and sometimes I have issues getting into gear as well.
 
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Remember that straight 6 has good low end torque, rarely do I need to go down 3 gears…. Usually 1 or 2. In mine those changes typically easier than spinning everything in the tranny with a 3 gear down moving shifting!

But I m an old guy too so never in a hurry !
 
I downshift, but only one gear at a time as far as 2nd gear. I wouldn't expect to be able to go easily from 4th or 5th to 1st. I go from 2nd to 1st only when I'm stopped, or just before I stop.
 
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You guys got it right. I think we're all on the same page. Of course we all down shift if say you're going up a hill and you see the RPM's going down and the Jeep slowing. Then ya pop it into the gear below.

I honestly just think that the AX-15 is a clunky trans. Powerful but clunky. Sometimes its smooth as silk and, maybe on a cold am it either feels like it hits a notch and you have to tug into 2nd. And other times its a smooth perfect match after its warm. And then sometimes its the same again with 2nd and even a little slow going into 3rd. Never a grind, but just a trans you can't always feather. And again, mine is low miles new. Maybe 20k on it at best. Original clutch master cylinder, though.

Alternatively, I have a buddy who also has an AX15 in his 89, as far as we know its original. He's owned it for approx 14 years and recently (2020) changed the clutch master cylinder at close to 200k. Interestingly enough, we noticed his clutch engages much later than mine. Meaning, he has to let up off the clutch more for it to engage. And mine is almost immediate.

Not even sure, but I don't believe the clutches are adjustable on these Jeeps. Can anyone confirm?
 
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