AX-15 5 Speed Shifting Problems - Suggestions Needed
 

I am looking for experience on the AX-15 5 speed manual transmission on a ’91 XJ where it can be hard to shift into first or second gear from a stop. Most likely 163k miles on the original clutch, etc. No grinding when trying to get into forward gears. The shifting issue seems to occur after fully warmed up. Once moving all shifts into all gears is smooth and without grinding. A down shift into first or second while rolling seems to be trouble free. Shifting into reverse can be either difficult or accompanied by grinding as if the clutch or throw out bearing is dragging. Clutch itself seems solid with no slipping.

When purchased less than 1k miles ago the owner reported that it was sometimes difficult to get the lever into reverse and I noted the same but there was no grinding initially. The previous long time owner seemed to drive a manual with skill and care. As part of changing all fluids I changed the transmission fluid with Chrysler recommended 10W-30 oil using Mobil 1 synthetic. I also flushed and bled the clutch hydraulics using low pressure on my pressure bleeder in order to get fluid to flow – this AX-15 has a bleed valve at the transmission. Linkages have been lubricated. The issues are more apparent after these tasks. I think I got any air out but probably should bleed again.

What is the most likely problem: clutch, throw out bearing, clutch master, clutch slave (located inside the transmission), air in hydraulics? It would be nice to avoid major transmission tear down if it is not likely synchro’s are at fault. Is the best strategy to plan for replacement of the clutch/throw out bearing plus clutch slave unit? Thoughts on clutch master plus slave hydraulic replacement as an assembly along with tubing? I have read that it is difficult to bleed without using a pre bled assembly but nearly impossible to install these as an assembled system. What is your experience if you have done this? Recommendations for next steps? Any other lessons learned on AX-15 work? I have no hands-on transmission experience. I believe I spotted a new looking clutch master unit at a salvage yard recently but I think the transmission was gone on that one. I can get that if it makes sense to start by replacing just the master.

The difficulty in shifting into first from a stop could be the master cylinder. Look in
the cabin where the master cylinder's plunger connects to the clutch pedal. Is there
any sign of oil leaking out the rear seal of the MC?

If the clutch and its hydraulics are the originals, then they are close to the end of
their use. My 98 is on its 4th clutch MC - the original and one other lasted 8 years each.

A new MC (Luk 357) costs about $40 so just changing that out is not too costly as a first
step, and see if it helps. I have no experience with the MC/slave pre-filled units.

If you're grinding going into gear from a full stop, that means the trans input shaft is still spinning, meaning dragging clutch. Now, figure out why.

Or seized pilot bearing.

I'm assuming you've done enough of these to look at the fork travel to tell if it's sufficient.

O.P. said NO grinding, just difficulty.

Sounds to me like less than full release of the clutch.

Also, I think that the "difficult to bleed" issues where folks suggest a pre-bled master/slave combo is specific to the external slave style AX15 starting in the 94 model year (note, my Dad got 400k 1 clutch job, still worked perfectly, etc. out of his 94 AX15 after teaching 3 teenage boys to drive a stick). Double check, but I think that the internal slave style of 89-93 isn't an issue bleeding. IIRC the master cylinders in general are just painfully difficult to bench bleed, so they are generally sold pre-bled... I'd start with a new MC and go from there. It may be difficult to replace, but I can't imagine it's as much work as pulling the tranny off the engine to do a clutch job.
If you do plan on replacing the disc/PP/bearings anyway, you might consider converting it to the external slave style if you can find a bellhousing in good condition for a good price.

Actually, OP covered that whole angle:

But as that transmission is (otherwise) fully synchro it would make sense that 1-2 is difficult instead of grinding when there is some clutch disengagement.

I had a case (Honda Accord) where the clutch pedal bracket had a split such that the resulting "give" prevented the master to become fully depressed.

Don't even ask what I did before I found it...

Sounds Like a normal AX-15 operation to me.

I've got one in my TJ an have driven them in XJs and YJs as well.

https://wranglertjforum.com/threads/...n-a-ax15.2469/
https://www.wranglerforum.com/f218/h...ear-86555.html
https://www.wranglerforum.com/f210/g...h-1856057.html


I'm not saying live with it, but mines been that way since I got it.
Proper Fluid helps a ton, but I see where you've changed it already.

Thanks for all of your useful inputs. I did check the master for signs of leakage at the clutch pedal side and found none. The rod was a bit sloppy though – wondering if it is worn and now shorter than it should be. Drove it today about 20 miles and got it as fully warmed up as possible for a 72 degree F day. That makes only 3 trips of any distance since the fluid change. Seemed better today. Really didn't have an issue going into first, but I was being a bit paranoid not to get stuck at an intersection with only neutral. If using a bit of a rolling stop while downshifting into first it was never a problem. At a dead stop and shifting into first was a bit tight a time or two but always possible. Reverse was sometimes OK, sometimes a little touchy with a tendency to want to grind if not done just right, whatever that it. Maybe synchros are cleaning up? Hard to say what fluid was in there, could have been original or possibly someone used a GL-5 and synchro’s are now seriously worn. Would not be surprised if the clutch release/throw out bearing is at end of life on what I believe is all original.

I think I will start with bleeding the clutch hydraulics again. I will investigate clutch pedal bracket and see if I can easily check clutch travel. Then try a fluid change using Red Line MT-90 or Pennzoil Synchromesh fluid and see what difference that makes as the issues, other than an occasional hard time selecting Reverse, occurred after the hydraulic fluid flush and gearbox fluid change to 10W-30. Although I like the idea of “sounds like normal AX15 operation” if those don’t help then a new master and/or clutch and bearing refresh. I would be interested in what an oil analysis of what is in there now might show. Probably enough residual old fluid and debris to get something from it. Or since this XJ will be going to my mechanically capable son soon maybe I will just let him deal with it.

good plan.

Also, try this after checking the pedal for the broken weld.

Sitting still with the Jeep off, pump the pedal 50 times and walk away for 20 minutes. Then see if it's better.

Update: I performed a pressure bleed of the clutch again being careful not to get any air in and did the pump the pedal 50 times routine several times. Still have the Mobil 1 synthetic 10W-30 in the transmission. Have Red Line MT-90 available now but have not switched over to it yet. I want to make one change at a time and see how it reacts. A couple hundred miles have now been put on it since the initial transmission fluid change and hydraulics fluid flush after which most of the problem occurred. The hard shift into first or second when hot is much improved to the point it is not a major concern. Still can get gear clash going into reverse but less pronounced. Son now has this ’91 so the next steps are up to him. I think two issues might have been at play – got some air in the system with the first hydraulic system flush and the clutch and/or throw out bearing are showing their age with 163k miles. And with wear the synchros of this 5 speed might not be as happy with the viscosity of the fresh & clean synthetic Mobil 1.

Another Update: My son has this XJ now and after another clutch hydraulic bleed most all of the issues have gone away or significantly minimized. There is MT-90 in the transmission now but the biggest improvement came after another bleed to get any trapped air out. Air may have entered when I first flushed the clutch hydraulic system. The reservoir has very little fluid volume. He did the last bleed on a bit of a slope to get the clutch master more level to help purge trapped air. Clutch pedal feel seems firmer. It’s probably due for a new clutch and pilot bearing but the lesson learned is try to avoid getting air into the system as it is very difficult to get out.