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AX15 Hard to Shift, Shuddering

Rattlesnake

NAXJA Forum User
Location
Wilmington, NC
I've been having an issue and can't seem to figure it out (or find any existing threads with the answer). Here's what's going on....

When I first start it up, sometimes I get some weird noises. Sometimes grinding, sometimes not, clutch in or out doesn't matter. But they always go away once I start driving. At this point, if the jeep is cold and has been sitting for awhile, it's easy to shift and the clutch works normally.

But after driving for awhile and the jeep has warmed up, when I try to slip the clutch starting from 1st the whole drive line (at least that's what it feels like) shudders. I've tried slipping it a ton and tried barely slipping it at all (that helps), but it still shudders pretty violently. 2, 3, 4, 5 gear shifts work fine. It's been doing this for several months now and I can't figure it out.

Also, in the last few weeks, it will occasionally be hard to put into gear, both when I'm moving and up/down shifting or when I'm at a dead stop. I can force it, but that's not a long term solution.

My first thought was either the slave or the master is failing. But the master is still less than a year old (replaced it with OEM myself), and it's full of fluid so it's not leaking at the slave. Also, the previous owner "replaced the clutch" about 2.5 years ago when it had 180k miles on it. What that means exactly is up to interpretation (the details have escaped my memory).

Any theories? I'm afraid I'll have to drop the tranny to fix it. Which means taking it to my mechanic since that's a little beyond my abilities and tool availability.

Stats: 1991 XJ, AX-15, 4L, np321, 220k miles.
 
could be a bad internal slave/throwout.

maybe a glazed clutch or the pressure plate springs are weak or broken.

what happens when you down shift?
 
I don't have a problem down shifting at all. Slides into gear with no worries.

I would be inclined to think it's the slave too since I have no reason to doubt it's never been replaced, but I would think I would be low on fluid in the master if that was the case. Maybe not. Plus pumping the clutch does nothing to help the "hard to get it into gear" moments.

The interesting thing to me is that all the shuddering is happening only when it's up to normal operating temperature. When it's stone cold it doesn't do it at all. Hmmm...
 
Not the tranny. It could be the internal seals in the master or slave are bad, which wouldn't cause an external leak, but would seal worse when the fluid heats up, thus not have enough pressure to engage the throw-out. I can't explain why a throw-out would get worse when heated up(when it's bad you can hear it and it's bad all the time). When this happened to me, I could see some rubber particles in the bottom of the master.
 
Thanks for all the feedback!

I knew the master had internal seals that could blow out, but didn't know if the slave had a similar design. Makes sense, and I won't rule it out.

I'm defnintely NOT hearing the throwout all the time. Just some noise occasionally, only during start up and the first 5 minutes after. Noise is there whether I have the clutch in or out (though it does change some).

I have no idea what all the previous owner did when he "replaced the clutch". So it could or could not include the pilot bearing. Haven't checked the bell housing bolts yet, I'll climb under there tonight and make sure they're snug.
 
Hey Rattlesnake, I've had very similar problems with my '92 starting about 21 months ago. Here's the story on mine, and you can compare it to yours. I bought it three summers ago in 2006, and it worked fine for a few months. Then it would shift fine when it was cold, but as it warmed up, it would actually start doing the exact same thing, and wouldn't want to go into or out of 1st gear. Sometimes this would happen on my way to work, at a red light, with other cars behind me.

First I replaced the master cylinder. That fixed the problem for a week or two (after I took the first master cylinder back--the first one leaked hydraulic fluid into the cabin one little spurt at a time very time I pushed the pedal). Then it started to do the same thing again. So after a while I brought my Jeep to a friend's place and he let me put it on jack stands and after several weekends of what seemed like endless work, I dropped the transmission and replaced the slave cylinder, which took all of like 30 seconds. I was being cheap, so I did not replace the clutch at this point. I reasoned that the slave cylinder was bad, since the clutch was not slipping, but rather grabbing and not releasing. That was a very stupid thought that I used to justify not spending the money on a new clutch. The book I was working from very clearly stated that if you open the clutch housing, all pertinent parts should be replaced since it is so much work to get it apart again.

I put it all back together again, and that fixed the problem. . . for another couple of weeks. Yep, I still had the same problem, but this time it was to a lesser degree. But it would often grind a little between shifts, and almost always going into reverse. So finally, after putting up with this for however long, maybe a year, I got around to buying a clutch kit and I started the work last Monday. It's not a quick or easy process, but the new clutch was in and tested as of last night. I did not re-replace the slave cylinder, which I hope I do not regret, but that's less important than what I found when i went in. First of all, the pressure plate, which I had come to suspect over the last year, was 1/4 in shorter than the new part. It was very obvious that the spring fingers were heavily worn. If you think about it, if the fingers are worn 1/4 inch, then that's a quarter inch of dead space when you press on the pedal during which time nothing is occuring, and that can mean quite a lot to whether you are actually disengaging the clutch or not. Second of all, the clutch disc was almost completely worn out. Not long from now, the rivets would have started grinding like crazy on the pressure plate and flywheel friction surfaces. There were maybe a few thousands of an inch between the rivet heads holding the friction material to the disc and the top of the friction material. It was very clear that both were in need of replacement. The flywheel looked brand new. I could hardly discern the difference between the worn and not worn part with my finger. The lesson I learned is that when you replace something in there, you should really check it all out. If you have someone do the work for you, you should also have them replace the clutch and pressure plate, and resurface the flywheel. I did not do this the first time around, and if you are paying someone to do this, most of the money to replace the $60 to $100 slave cylinder--you have an internal slave/throwout bearing for your model year--you will still be spending a lot of money to have the transmission dropped. I would strongly advise that you drop the money for the clutch parts as well. Or pay the same labor fees twice, because it's very little extra work to actually remove the pressure plate and flywheel.

That's my two cents, and I'm really coming out strongly with it because I suffered it out for about a year knowing that I f-ed up not replacing the clutch to begin with while I had the tranny dropped. It took me this long to get the motivation up to do that whole big job again. And who knows what I did to the gears or synchros in that time. I tried to baby it, but I wheeled it, too, so that's not exactly babying it.

My '92 currently has 192,XXX on the clock. I like it much better with the new clutch. Good luck with your fix. Reading your post was like reliving my last two years. Each time I replaced a hydraulic part, it would seem to be fixed for a while, and then it would return to driving like crap and grinding. I just started driving on the new clutch, so time will tell with that, but the parts were definitely worn out and in need of replacement. I couldn't tell you how long ago the clutch was put in, since I've only had it for about 20,000 miles, but I did notice the flywheel was like new, so I doubt it was so very long ago. The quality of the parts going in will have a lot to do with how long they last. I put in an aftermarket Zoom clutch with a Kevlar surface. Hope it doesn't suck, 'cause I never want to do that job again!

--wavingpine
 
Wow, thanks a ton, Wavingpine! I really appreciate you taking the time to type all that out. It really helps a bunch. :)

So your 92 is running better now I hope? Sounds like I'll be taking it in to have them drop the tranny and see what's going on. Thanks for the advice on not cheaping out and avoiding replacing all the other clutch parts. I'm sure I would have been tempted to skip it...

I'll update this thread when I either get the issue resolved or figure out what's going on.
 
No problem. I saw the title description and thought I'd tell my story because it has been frustrating chasing the trouble down for such a long time. My Jeep is shifting much more smoothly now. There's just a little hang up on reverse sometimes, but that may be due to my having run it so long like that perhaps doing some damage inside the tranny. I need to bleed the clutch hydraulic system out again to make sure that there's no air in the line. I used the one person under the car opening and closing the bleed valve and the other working the clutch method, which is as good as I could do at the time. I have a Motive brand power bleeder that I actually got when I did brake work on my STi that I'm going to use to re-bleed the clutch soon.

On the STi, there are two bleeder valves per caliper, so that can be a very labor intensive job. With the power bleeder, I got it done right the first time. In fact, it was so easy, it almost made me laugh compared to the time I did the brakes on the Cherokee with its simpler single bleeder set-up, which seemed like a real pain at the time. I found an extra master cylinder, which I'm going to drill a hole in the cap of and attach a hose barb and hose so I can use it with the power bleeder, which should assure that my hydraulic system for the clutch is air-free. In your case, a shop should be able to do everything just fine. Even if the clutch doesn't absolutely "need" to be replaced, it's better to have it done while it's alrady accessible since labor alone would be so much to have the process done twice. In my case, I definitely needed new parts, though.

Hope it all works out for ya!

--wp11
 
hiya all... still have the same problem, but I'm beginning to suspect the rear main seal as opposed to anything clutch related. Why? Well, I was under the jeep poking around and there is oil pretty much everywhere. All over the transmission, and the transer case as well. There was even a drip getting ready to drop right from the lowest part of the bellhousing.

Here's my theory... oil is leaking from the RMS, getting on the flywheel, and that's what's making the clutch extra grabby and causing the shuddering. It also makes sense that I'm only noticing it after the jeep is up to operating temperature (as I mentioned before my clutch is perfect while it's cold or warming up), since that's when the leak should really be flowing. What do you guys think... make sense?

I'm going to clean everything up real nice and then pay attention next time I take it out as to where the leak is coming from.
 
Well, I agree that you can have a shuddering effect if your clutch disc is contaminated with oil, but that should be an issue with engagement, and the grinding gears sounds like a separate issue related to the clutch and/or associated hydraulic components and their effect on incomplete disengagement. After driving mine for a week with the new clutch, I'm finding I still have some disengagement issues as well. The new cltuch is working great, but I'm suspecting the substandard e-bay slave cylinder that I put in a while back is leaking internally, meaning that when the piston pushes, some of the fluid is escaping past the seal inside the assembly, preventing a complete stroke of the piston, and resulting in incomplete disengagement of the clutch. I'm going to buy a true OEM slave cylinder when I feel like dealing with this again, which will be prior to it being too cold out for me to work.

I also find that when cold, I have less of an issue, but my rear main seal is not leaking.
 
Did you get this figured out? I'm having a similar problem with mine. I have done the clutch and slave already.

To whom are you addressing this question? Speaking for myself, my problem with hard shifting has not completely gone away, but it improves once the vehicle warms up. Until then, I push gently on the gear shifter until the gears are ready to mesh so I'm not grinding the hell out of them, and I shift into first before I go into reverse.

I got sidetracked with replacing the u-joints in the front axle and the pinion yoke on the rear axle and never installed my second slave before it chilled off here. The next thing I'm going to try is a reverse bleed on mine. I'm thinking that trying to push air bubbles several feet downwards may not be the easiest thing to do. The clutch hydraulics are notoriously hard to bleed, so I'm going to try the reverse route with my power bleeder, which is nothing more than a sealed bottle with an air pump handle built into the top of it, which will allow me to push fluid the other way (hopefully not too quickly for a helper to suck the excess out of the reservoir).

--wp11
 
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I have found that cheap gear oil causes poor cold shifting. Switching to something like Redline MTL will likely improve that for you.


I actually find that to be extremely interesting because I noticed that shortly after I changed the gear oil (after I had first replaced the master cylinder) that the shifting seemed to get worse, so then I replaced the slave cylinder, which greatly improved but did not completely resolve the hard shifting problem, and then I replaced the flywheel, clutch disc, and pressure plate later. I had thought that the gear oil switch was just coincidental with hydraulic problems. My brother in central PA is borrowing my 5 speed Jeep right now while I work on the one he usually drives, but when I get it back, I'll swap out the oil for a quality brand. I know I used generic parts store oil when I drained and refilled the case.
 
I actually find that to be extremely interesting because I noticed that shortly after I changed the gear oil (after I had first replaced the master cylinder) that the shifting seemed to get worse, so then I replaced the slave cylinder, which greatly improved but did not completely resolve the hard shifting problem, and then I replaced the flywheel, clutch disc, and pressure plate later. I had thought that the gear oil switch was just coincidental with hydraulic problems. My brother in central PA is borrowing my 5 speed Jeep right now while I work on the one he usually drives, but when I get it back, I'll swap out the oil for a quality brand. I know I used generic parts store oil when I drained and refilled the case.

what type of gear oil did you use? gl-5 is not recommended for the ax-15. you need a gl-3 or a gear oil specific to manual transmissions such as the redline mt or the thinner mtl.
 
what type of gear oil did you use? gl-5 is not recommended for the ax-15. you need a gl-3 or a gear oil specific to manual transmissions such as the redline mt or the thinner mtl.

Honestly, I can't remember which I used. I'm definitely up for swapping it out ASAP though, to see if I can get a cold shift performance enhancement. I've just been reading the various posts here on which oil one should use and there are many different opinions. Trying to sort it all out. . .
 
Without a doubt, one of the best things that I ever did for my AX15 was to drain the dino juice, and get a good synthetic GL3 oil (Redline is what I used) in there. Made a huge different in the Upper Midwest in the cold weather for shifting.
 
Without a doubt, one of the best things that I ever did for my AX15 was to drain the dino juice, and get a good synthetic GL3 oil (Redline is what I used) in there. Made a huge different in the Upper Midwest in the cold weather for shifting.

I looked up the Redline MT-90 on Summit Racing's site and the is an additional information button with a write-up from Redline stating that the MTl and MT-90 are both GL-4 rated. Is this OK?
 
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