Whaddup. My ‘95 XJ is great when entering first, second, and fifth gear, but periodically when shifting into third and fourth, it will grind right as I insert it into the gear. Grinding isn’t long and is just as I place it into gear, and doesn’t always happen and is almost random. Anyone ever run into this? Is the the synchro?

 

Have you ever changed the fluid? If not I would start with that, use a good quality fluid like Redline MT90.

 

I would actually second that, my AX-15 always had issues with "hard" shifting. The fluid that was in there came out like water. I replaced it with some 10w40 motor oil which helped alot, but putting Redline MT-90 made it feel like a new transmission.

But at the same point, it could be the synchros being worn out. I would say throw some new fluid in and see how it reacts. If it gets better, pony up for the MT-90 ($70 or so for the fluid).

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Syncromesh is whats best .

 

Oil wars!!!

I have the Redline MT-90 in my AX-15 and it is fantastic.
I had Syncromesh in the NV3550 in my TJ and it was also very nice for the several months between the fluid change and my tranny blowing an internal bearing (I'm not suggesting they're related - the Jeep had 305k miles on it).

 

What syncromesh are you referring to? If its Pennzoil Syncromesh that is a lighter weight fluid that is designed more for manual transmissions that originally speced atf, I run Pennzoil Syncromesh in my ZF6 speed in my truck and it shifts great, but the AX15 specs a 75w90 gear oil which is why I recommended the MT90 because it is a gear oil made for manual transmissions, you can't just put any 75w90 gear oil in it because the additives that come in the newer gear oils are bad for the syncros.

 

Max - before this thread devolves into debate regarding the oil type, let's consider your problem.
You have grinding in 3 and 4, but not in 1,2,5,R. Therefore it is unlikely your issue is as simple as "low fluid". It is probable that you have worn synchros or a worn fork or something to that effect.
Having a proper fluid level may help your problem, but on a 23 year old vehicle with hundred(s) of thousand(s) of miles you may be looking at rebuilding or replacing your transmission.
You can try to change the fluid and minimize the problem - so you should be aware of the following:
As mentioned, modern gear oils are bad for the AX15 as they can damage the synchros. Too much sulfer, I believe is the problem.
MT90 is designed for the AX15 type tranny, it won't damage the synchros, it's full synthetic and is widely considered the best fluid for the AX15 - it is expensive though.
Some people do use other things like motor oil, synchromesh, etc despite it not being the "proper" fluid.
I was told synthetic gear oils (like a Mobil one) is safe to use and won't damage the synchros.

What I would do if I were you, considering your problem is either:
A - Replace the fluid with MT90 to be 100% sure fluid level/quality is not the root problem and you don't mind spending the money.
or
B - Top off the fluid with a quart of Mobil One 75w-90 (at about $10-ish) if you don't want to spend the $$ on MT90 and see if the grinding improves or goes away. Then depending on how it drives, decide where to go from there. If it's better, then maybe you can justify the cost of the MT90 and do a full change of the fluid. As Investinwaffles mentioned.

If the fluid doesn't make any difference, then you can figure out what you want to do for your unique situation.
Napa sells a rebuilt AX15 for about $1700, but it may be cheaper to have a local shop rebuild yours if that's the direction you want to go.