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Discussion Starter · #1 ·
'89 4.2 with ax15

I can't shift into first if I'm going over 10mph. When I slow down it shifts fine, but over that nothing. It doesn't grind or anything, it just won't go.

1st to 2nd grinds most of the time, every once in a while it will make a loud pop and go in, and sometimes it shifts smoothly with no problems.

2nd to 3rd grinds every time, but just a little. It's almost inaudible, but I can feel it through the gear shift.

3rd to 2nd it won't do ever. No grinding, just nothing. The gear shift just stops short like it's hitting a wall.

4th and 5th always work perfectly.

Any ideas as to what could be the cause of this? I checked clutch disengagement, and made sure fluid was full.
 

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'89 4.2 with ax15

I can't shift into first if I'm going over 10mph. When I slow down it shifts fine, but over that nothing. It doesn't grind or anything, it just won't go.

1st to 2nd grinds most of the time, every once in a while it will make a loud pop and go in, and sometimes it shifts smoothly with no problems.

2nd to 3rd grinds every time, but just a little. It's almost inaudible, but I can feel it through the gear shift.

3rd to 2nd it won't do ever. No grinding, just nothing. The gear shift just stops short like it's hitting a wall.

4th and 5th always work perfectly.

Any ideas as to what could be the cause of this? I checked clutch disengagement, and made sure fluid was full.
Not sure what method you used to check clutch disengagement as you state, but everything you describe is indicative of incomplete clutch disengagement.
 

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I agree with clutch disengagement but it could be as simple as improper gear lube and or fluid level. It shouldn't downshift into 1st gear above 10mph at least both of mine never do. Could try shifting slower if you're trying to shift it fast both my AX5/15 don't like that either.

Many use 10w-30 full synthetic motor oil in the AX transmissions definately don't want to use GL5 gear oil. It's not yellow metal safe and will eat the syncros.
 

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Discussion Starter · #4 ·
For clutch disengagement, I jacked the rear axle up, put it in gear, and let out on the clutch until the rear tires started to move. It took about 3-4" from the floor before the tires began to move.

I'm pretty sure it just has standard gear oil in it based on the smell.
 

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So first thing, a little more information is needed.

1-Is this a new problem that showed up rather quickly or suddenly?

2- Are you sure this is an AX-15, 89' was the transition year from the BA-10 if I remember correctly. My 89' originally had a BA-10.

3- If it is an AX-15, is it a swap and does it have an external slave cylinder. (Both the BA-10 and the early AX-15's had internal slave cylinders)

I agree that it does sound more like the clutch isn't fully disengaging. If the incorrect oil was used and the synchros where shot he should still be able to shift, there would just be more grinding.

No matter the answer to the above questions I would look at the following.

Check the clutch fluid level. If it's really low that could have let some air in the system.

If it's not low, I would bleed the clutch anyway. Could still be some air in the system.

If there's a leak and you have an external slave cylinder then it will be easy to fix. If it's internal then the transmission has to come out (Assuming it's a slave cylinder leak). Also if there's a leak, it could be on the master cylinder, my original one for my 89' leaked at the master cylinder, inside the cab up under the steering column where it comes in. The replacement master cylinder did the same thing infact and I am currently using the rebuilt original.

I hope this helps you out.

Sent from my moto z3 using Tapatalk
 

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Discussion Starter · #6 ·
1. The jeep is new to me, but it has done it for as long as I've had it ~250 miles on it.

2. It has the ax15.

3. I don't know about the slave cylinder. The clutch line runs into a rubber grommet on the bellhousing, and a small piece of line also runs out of it with what looks like a brake bleeder on it.

The fluid level is topped off and hasn't changed since I bought it.

Is there some other way to test for disengagement?

It could be my imagination as well, but the longer I drive it, the better it shifts. If I just run up to the gas station a few miles down the road and back, it never will shift down into second, but if I go for about a 50 mile cruise, when I come back, everything seems to shift better, and every once in a while, I can get it into 2nd from 3rd.
 

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If the clutch has air in it it will usually feel feel soft at the top of the pedal and then harder near the bottom of the throw. Commonly referred to as a spongy feel.

It won't hurt to bleed the clutch if you think there could be air in it. And the only cost is some brake fluid.

On the other note, since it gets a little easier to shift after 50 or so miles, that would be the transmission fluid warming up. Although that's a pretty long time for that to take. Even in the winter when it's cold out it doesn't take that long for mine to start shifting a little easier in the morning. And I have gear oil in mine.

Since the YJ is new to you anyway. It's pretty common practice to change all the fluids when you get a new vehicle. Never know what the previous owner did. So a fluid change could be in order. Again it won't hurt and isn't very expensive either.

As was said earlier a synthetic 5W30 is an acceptable fluid choice since finding the correct gear oil is an issue with the brass synchros. I used it in mind for a while. And it worked fine, but once it warmed up it felt to thin for me. So I changed to Royal purple gear oil that's yellow metal safe and like the way it shifts. 5W30 is cheap and easy to get so it's a good choice to try and see if that works as well.

It really does sound more like the clutch not fully disengaging than the gear oil. However, if there's no leaks and no air in the clutch line then the next thought is an internal transmission problem. And sometimes a fluid change can help until a rebuild is done.

How many miles are on the Jeep?

Sent from my moto z3 using Tapatalk
 

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I agree with the above suggestions. The very first thing I'd do is bleed the clutch. Then I'd change the transmission fluid. If switching to 5W or 10W-30 motor oil (even better is the Royal Purple yellow metal safe gear lube) doesn't work think about this....

You may have worn syncros from a PO using GL5 transmission fluid or from the PO bashing the gears. At 105K miles I'd be surprised if that's the case unless the PO really abused the vehicle.

Let us know how it goes.

Good Luck, L.M.
 

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Discussion Starter · #10 ·
I don't know about the PO. The jeep seems to be something of a mystery as some things are very well taken care of and some are not.

I changed it out the transmission fluid to royal purple, and it shifts better, but still not good. When it goes in gear, it does it much easier, but all the problems still persist including the not downshifting into 2nd. I guess bleeding the clutch will be the next project.

The old fluid looked like this:


And the magnet on the drain plug had a good bit of fine metal on it as well. I'm not sure if there is hope for this one.
 

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Hopefully the bleeding helps out.

As far as the color, with out knowing what was used or how long it's been there to begin with it's hard to say.

The metal on the plug is kind of normal, if it's little thin almost like whiskers that's not bad. Again it's hard to say since you don't know how long since the last change. On the other hand if you find small pieces of metal with machined or cast corners then that's a problem.

Good luck and let us know how it goes.

Sent from my moto z3 using Tapatalk
 

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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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Even if your clutch fluid is full, the fluid can absorb moisture and break down the fluid. I would bleed it out completely, Three our four full reservoirs should do it. I had soft brake response a few years ago and completely bleeding all four lines and replacing all the fluid gave me much better brake response till I got around to changing them out. Same principles apply to your clutch.
 
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'89 YJ 4.2 with MC-2150 Carb & HEI, 2-1/2" Ex. AX-15, NP231 SYE, Adams shafts, F&R ARB, 3
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PS, Very few 89's came with the AX-15 are you sure that is what you have in there?
 

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For clutch disengagement, I jacked the rear axle up, put it in gear, and let out on the clutch until the rear tires started to move. It took about 3-4" from the floor before the tires began to move.

I'm pretty sure it just has standard gear oil in it based on the smell.
That would be engagement.

While you had it in the air (with the front tires chocked) you could simply: 1) Kill the engine. 2) Make sure the trans. is in 1st gear. 3) Have someone depress the clutch fully and hold it to the floor (THAT is disengagement). 4) See if the rear tires spin by hand with little effort.

Keep in mind if it is an open rear differential you may need to have someone hold the opposite tire you want to spin, or leave one rear tire on the ground.
 

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The BA10 has a split main case. In other words, it has a seam between the left and right halves. The seam is visible from under the Jeep as are the bolts that hold the two halves together.
An AX 15 has a main case, an intermediate plate and a rear section. The cases are whole and there is no seam nor bolts.The intermediate plate is aluminum. If you have an iron intermediate plate you have an AX5.

Post a few pics if you have any further questions. You can also Google AX5 vs AX15. The best information is on the Novak sites.

Good Luck, L.M.
 

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It's definitely not a bA-10. There's no lengthwise seem and it has the intermediate plate.
Take a magnet and see if it sticks to the intermediate plate. If it doesn't stick, you have a AX15. If it sticks, start looking for an AX15 transmission and transfer case. The reason I add transfer case, I believe there are spline count differences between the AX5 and the AX15. Check me on that though.

Good Luck, L.M.
 

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I don't know about the PO. The jeep seems to be something of a mystery as some things are very well taken care of and some are not.

I changed it out the transmission fluid to royal purple, and it shifts better, but still not good. When it goes in gear, it does it much easier, but all the problems still persist including the not downshifting into 2nd. I guess bleeding the clutch will be the next project.

The old fluid looked like this:


And the magnet on the drain plug had a good bit of fine metal on it as well. I'm not sure if there is hope for this one.
Looking closely at the pic of the fluid, it appears that there are little specks of brass on the shop towel. If so, the brass specs are probably worn bits of your syncros. Maybe a PO gave the Jeep to a new driver so that the new driver could learn how to drive a standard shift.
In any case, if I were you, I'd at least plan on replacing the syncros or locating a known to be good replacement AX15 transmission. The issue with only replacing the syncros is what else you might find as you disassemble the trans and inspect the working parts.

Do the cheap & easy things first. Even if they don't improve the shifting, you've eliminated those things as causes of your shifting problems.

Let us know what you find and how you plan on proceeding.

Good Luck, L.M.
 

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Yes, the AX5 is 21 spline The AX15 is 23 spline
 
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Discussion Starter · #20 ·
So if I do need to replace it, what does everyone recommend? New, used, Rebuilt? From where?

There is no place local to get a used transmission, and I don't trust anyone around me to rebuild it.
 
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