Are my synchronizers toast?!

[InTacosWeTrust]

In my 87 4wd 4.0, the po put an

ax-15 in it the 1st gen 90’s one. Since having the truck I’ve replaced a new master and slave, along with the luk 01901 clutch kit around a year ago, the guy that replaced it for me also changed the transmission fluid, fast forward to around a couple months or so after, I noticed slight grinding to shift into 4th, now about a whole year later only when the trans gets hot and especially when it’s really hot outside, (the cooler weather doesn’t really affect the shifting at all) it’s hard to shift into 2nd, 3rd and 4th with binding and grinding and I have to slam it hard into gear, and sometimes when I try to shift from gear to gear it feels like it binds, almost like it is still in gear, when the shifter is in the neutral position and clutch pedal is still pressed in, like the shifter pulls the gears into neutral and it’s not free and all. I’ve already planned on changing my and purchased the transmission fluid to redline mt-90, but haven’t done it since a week later since I bought the fluid it started doing this.

 

Should I buy a new transmission? Change the fluid and see if it fixes it? 
Take it to a transmission shop and have them replace the synchronizers?

Theres alot of options, some cost more than others, I’m not made of money but I also want to know what is the best or a good solution to fix this issue, any advice on what this issue with the transmission could be? And what solution I have or haven’t thought of would be best

 

[rokinn]

Check your clutch fluid level.  If it's low fill it and see if that helps.  Internal slaves seem to have a high failure rate with new installations (chinese crap).  If it is the slave leaking don't replace it, convert to an external slave.  That way when the slave fails next time you won't have to pull the transmission.

 

Is the oil level in the transmission at full?  Perhaps your transmission is leaking.

 

Get a professional opinion.

[Pete M]

definitely could be the clutch not fully disengaging.  I would try bleeding it. 

[89 MJ]

I am also leaning towards the clutch not fully disengaging. Like they said, check the fluid level and try bleeding the clutch. Depending on how many miles are on the transmission, it might be getting to where it needs synchros though. 

[eaglescout526]

Aren’t AX15’s supposed to use 10-40 oil. 

[89 MJ]

If I remember correctly, the AX-15 is supposed to take full synthetic 10W-30. I think a lot of people use the Redline though. 

[Eagle_SX4]

I also think you should start by making sure the clutch is bleed properly. If you have an internal slave cylinder they are known to be an issue and don't last very long. It could be that is what has failed and not your synchros.

 

As far as fluid goes what ever you use just make sure it is yellow metal safe. Most gear oils have sulfur in them which dissolves brass synchros.

 

I am running Schaeffer's Supreme Gear Lube 75W-90. Redline MT90 is also a great option. Both of these are yellow metal safe 

 

[Eagle_SX4]

Also when you change the fluid in your transmission look at the fluid closely. If your synchros have failed the fluid will be full of small pieces of brass. (gold colored metal pieces)

[ghetdjc320]

I’d second checking the clutch first as well. As for tranny fluid, I run 10w30 motor oil as suggested by the old mopar tsb. 

[87MJTIM]

Your symptom are a little similar to mine.  I have trouble shifting in 1st at a stop when warm.  Shifting out of 1st into 2nd is very notchy.  All other gears are "fine," just slightly notchy.  Reverse is ALWAYS grinding, unless I shift into 4th then R.

 

I too was wondering if my synchroes were going bad.  My searching the 'net lead me to a bad hydro clutch system.  See attached https://www.jeepforum.com/threads/ax-15-won't-go-into-1st-when-warm.748660/?post_id=6969186#post-6969186

 

I have a "pre bled" hydro clutch.  It does not have a bleed screw.  I tried to follow some videos on "gravity" bleeding the clutch.  Remove the whole system from the vehicle.  mount the master cyl up high, with the slave cyl down low.  Slowly pump the slave push rod to force any air up to the master.  This method has not solved the problem.

 

Has anyone ever disconnected the line from the master cyl, drained the hydro fluid and added fresh fluid?  The line is held in by a roll pin.

[89 MJ]

27 minutes ago, 87MJTIM said:

I have trouble shifting in 1st at a stop when warm.  Shifting out of 1st into 2nd is very notchy.  All other gears are "fine," just slightly notchy.  Reverse is ALWAYS grinding, unless I shift into 4th then R.

Mine is the same way, except it’s notchier when it’s cold. It’s been this way since it was rebuilt 10-15k miles ago. Reverse grinds because it doesn’t have a synchro. The only time my reverse doesn’t grind is when I sit stopped for a second, then go for reverse. I haven’t tried your 4th to R trick though. 

[watchamakalit]

18 hours ago, 89 MJ said:

Mine is the same way, except it’s notchier when it’s cold. It’s been this way since it was rebuilt 10-15k miles ago. Reverse grinds because it doesn’t have a synchro. The only time my reverse doesn’t grind is when I sit stopped for a second, then go for reverse. I haven’t tried your 4th to R trick though. 

When I was taught to drive manual I was taught 1st to reverse. became habit to throw it in first to stop trans rotation, then on to reverse. Stops the grinding and easily becomes thoughtless habit in short order. 

[PIKE]

Another vote for Redline gear oil.

 

Shortly after i Purchased my new pickup in 1989 I read that regular dino gear oil would eat away at the brass synchros. I choose the Redline 75w90NS. The NS does not have any friction modifiers to help syncros when shifting. The Redline is also safe for use with all synchro materials. The 75w90NS is rated as GL-5 which is what my owners manual specified at the time. 

I'm not going to say I noticed any difference or improvements, but what I will say is that after 36 years my AX-15 still shifts like it did on day one.

 

https://www.redlineoil.com/75w90-ns-gl-5-gear-oil

 

I also agree it could be your clutch. Cruiser would tell you to pump your clutch peddle rapidly about fifty times, let it rest for twenty minutes then see how it works.

[InTacosWeTrust]

All I have done so far since I’ve been so busy, is drain the fluid. fluid looks kinda dirty not really that bad, slight small metal shavings gunk on the drain bolt, but when I drained the oil out of the tranny, a lot of it came out of the fill hole first… is that normal?… which caught me by surprise, then I unscrewed the drain bolt and then the rest came out from there

[ghetdjc320]

If you're on level ground, it may have been overfilled. I have filled mine using the shift tower on occasion but I leave the fill plug open to set the correct level. If the fill plug is left in I could see how it could get overfilled easily. I wouldn't be greatly concerned about that though or the presence of some brass dusting.

[pizzaman09]

A lot of good advice in this thread.  I agree that this could and likely is a not fully disengaging clutch.  I'd bleed it and see what happens.  Also changing the trans fluid can be a good idea.  I've personally used Royal Purple Syncromax in my AX-15 and it helped it shift better.  I've also used MT-90 in transmissions in other cars with similar results.  

 

16 hours ago, watchamakalit said:

When I was taught to drive manual I was taught 1st to reverse. became habit to throw it in first to stop trans rotation, then on to reverse. Stops the grinding and easily becomes thoughtless habit in short order. 

This is typical non syncro methodology.  My Austin Healey has no syncro on first or reverse, I always shift into a synchronized gear, usually second to stop the shaft rotations.

[Htchevyii]

The Redline has worked best for me. I wouldn't count out a bad LUK slave cylinder though, mine completely failed with 10,000 on it. I swapped to an Advance Adapters external unit and haven't looked back. 

https://youtu.be/X2BxkXxtwXU?si=UFPvqo2XcJtZ2KuU

[watchamakalit]

When i swapped mine to external, there was an assembly available that was a master,slave,and the line connecting them already pre-bled. If it's still available it made the job much easier. Pretty much eliminated any fluid mess. 

[InTacosWeTrust]

So what is a good external slave adapter? I’ll probably replace the clutch, master, and slave as well, is there a good heavy duty kit? 
I’m lifted on 8 inches w/ 35s I plan on going to bigger tires in the future, turning this truck into an overland/ off road vehicle that I do want to drive on road on occasion 

[89 MJ]

50 minutes ago, InTacosWeTrust said:

So what is a good external slave adapter? I’ll probably replace the clutch, master, and slave as well, is there a good heavy duty kit? 
I’m lifted on 8 inches w/ 35s I plan on going to bigger tires in the future, turning this truck into an overland/ off road vehicle that I do want to drive on road on occasion 

If I were to do it, I’d use all of the advance adapters parts linked in this video:

10 hours ago, Htchevyii said:

The Redline has worked best for me. I wouldn't count out a bad LUK slave cylinder though, mine completely failed with 10,000 on it. I swapped to an Advance Adapters external unit and haven't looked back. 

https://youtu.be/X2BxkXxtwXU?si=UFPvqo2XcJtZ2KuU

 

[Htchevyii]

I used the Advance Adapter kit as shown in the video. I would have gladly used used Jeep hard parts if I could have found them readily available locally. By the time I pieced it all together and paid a bunch of separate shipping, it wasn't worth it. The AA kit allows the use of the original clutch master with a stainless braided line and adapter to the new slave. I did use a new BCA throughout bearing because the AA one looked kind of cheap. I actually even bought a brand new AX15 from AA and swapped it out at the same time. I don't think that it cost much more than rebuilding my high mileage one would have.  We drove home 500 miles without a clutch on that trip. 

[ghetdjc320]

The AA is a good kit. Grab the best throwout bearing you can find though. Or, just stick with a quality internal slave setup and run Redline, 10w30 synthetic motor oil or whatever else works with the brass synchros. Luk Rep-Set has been a pretty good clutch option. Going over 8 lift on 35's will help you refocus to other problems aside from the tranny  

[InTacosWeTrust]

9 hours ago, ghetdjc320 said:

The AA is a good kit. Grab the best throwout bearing you can find though. Or, just stick with a quality internal slave setup and run Redline, 10w30 synthetic motor oil or whatever else works with the brass synchros. Luk Rep-Set has been a pretty good clutch option. Going over 8 lift on 35's will help you refocus to other problems aside from the tranny  

You have me curious on what other problems may occur since I’m over 8 inches lol, I have a Dana 30 in the front, and the 8.25 in the back and I am re-geared to 4.88. With working 4wd. Just trying to see what I missed and needs to be covered

[InTacosWeTrust]

Does anyone have any insight on these m-pact clutch kits off rock auto?

I talked to one of the techs over the phone to gain more insight and overall for my use of the truck and applications he recommended the M-PACT 01034WSST1X Clutch kit

[InTacosWeTrust]

10 hours ago, ghetdjc320 said:

The AA is a good kit. Grab the best throwout bearing you can find though. Or, just stick with a quality internal slave setup and run Redline, 10w30 synthetic motor oil or whatever else works with the brass synchros. Luk Rep-Set has been a pretty good clutch option. Going over 8 lift on 35's will help you refocus to other problems aside from the tranny  

when I replaced my clutch, master and slave a year ago, I replaced it with the LUK 01034 Clutch Kit, I’m not denying it, but honestly it’s hard to wrap my head around and believe that the slave, or even clutch has failed since everyone in this club pretty much recommends and says it’s one of the best kits to get, but things do fail no matter how many good reviews, it’s just hard to believe you know, but like Htchevyii said, his failed after 10k miles.