I have a 94 xj with the ax15 manual. Recently I noticed some weird noises when slowing down. Everything sounds fine and normal when I'm accelerating or on steady throttle, but when I slow down, and in gear, I hear almost what sounds like a racheting sound from the tranny area. If I take it out of gear then I hear other little clunks.

Also, without fail, everytime when I'm slowing down, as soon as the speedo hits 20 mph I hear one quiet clank and I can't pinpoint from where?

I have big tires but no lockers or anything like that.

 

One question: Do you keep your clutch pedal down when decelerating?

 

Not usually. And to clarify if I'm in gear decelerating in 4th or 5th gear (clutch pedal not depressed) I get this weird ratcheting sound from the tranny. I don't notice it when I'm not in gear or in lower gears. If I press the clutch in while this strange ratcheting is happening it stops. And then is back again when I release. This is consistent.

The weird knock only happens when in neutral slowing down between ~35-20 mph. And that is almost sounds like a drive shaft knocking against something but at 20mph there's one louder knock and then it's gone

 

I pulled the rear drive shaft today to check to see if I have play in my rear diff pinion and it it doesn't feel like it but truth be told I don't have experience with bad diffs. I am gonna replace the ujoints while its off though. Just looking for other things it could be

 

So I swapped the ujoint on the back of the DS that goes into the diff. The front one was in great shape so I didn't swap it. I still get a weird knocking sound every once and awhile when slowing down. Pinion bearing? Something else inside the diff? I don't know what else it could be

 

Check your tranny and motor mounts. For the tranny, use a pry bar and see if you can move the transmission by "hand" (in other words, prying on it), it shouldn't move without a pretty good "oomph"). For the motor mounts, if you can see any cracking or if the engine vibrates in the engine compartment when idling, you need to replace the mounts.

Also I'd do a fluid change on your transmission (I use MT90 and love it - but it's a little pricey - some use Pennzoil Synchro-mesh or even motor oil.. I wouldn't use motor oil but some guys swear by it) and transfer case (Regular Dex/Merc 3 Auto transmission fluid) just to be sure.

 

I just replaced the motor mounts with some brown dogs a few months back so I'd be shocked if they were bad. I will check out the tranny mount though. It had been holding things up when I had some bad motor mounts so it might have gone too.

When it comes to the fluid change in the tranny, I know with auto trannys it's said you either change it regularly and often or never ever. Are manuals the same way or no? I ask because I have never changed it in the 10k or so miles that I've owned the jeep and I have no idea if the previous owner did either.

 

Manual is completely different. Automatics require the fluid as a component of their operation, manuals require fluid strictly for lubrication. Change it, change it now.

Also the "never change it" thing with automatics is of dubious legitimacy, but as a manual transmission guy, I can't speak to that.

 

Okay thanks. I'll get that changed and update.

 

Its not a transmission if you manually shift it, it's a gear box. Clutch, pressure plate, throw out bearing. It could be the pressure plate springs are giving up or the clutch surface is chattering when you decel. Or even the throwout bearing is going. Good news is you replace all three at once and get another 100k+.

 

So I finally got the chance to change the fluid out. Out came the mud, in went the synthetic 10w-30 since that's the only thing non-gl5 I could find locally.

Everything went fine. Took the jeep for a drive. The chattering in 5th while coasting is still there. I don't wanna have to replace the throwout bearing and pressure plate but if I must I must...

Also still present is the weird knocking sound I get in neutral between 25-15 mph. I noticed it seems to be syncopated with 2nd gear or at least close. (I found that out because if I try to down shift into 2nd I can feel the gears clicking on the shifter) thoughts on that sound in particular?

Thanks, all

 

My gut feeling on the matter is that you're looking at a new clutch set. 2nd gear is difficult to get into on an AX15 and it sounds like your clutch is not fully released when you're shifting. Since weak plate springs would explain that and the chatter.

Someone didn't happen to put a NV3550 in the Jeep, did they??
That P.O.S. transmission rattles badly in neutral (the head Jeep mechanic for the entire east coast assured me this was "normal", of course).

 

I don't think so? I replaced the master and slave cylinder awhile back and what I got said it was for an ax-15. (external slave). Are those parts interchangeable? How would I tell if it's the nv3550?

As far as the clutch not fully releasing, would that explain why sometimes if I shift into the wrong gear and then correct my shift without releasing the clutch and depressing it a second time, the shifter doesn't want to go in? Or is that just bad synchros? (which is also something that's likely on 2nd and 3rd for me since they tend to grind more than the other gears even if I'm pressing the clutch all the way while downshifting)

 

Also, I say the sound is syncopated with the 2nd but that could be nothing. The sound still seems to come from the rear of the vehicle but I don't have anyone else who drives manual to test while I crawl around listening for it

 

I'm being facetious about the NV3550 - they are interchangeable, but the NV's were only used for 4 years in Jeeps (00-03 or 04).

You definitely have a clutch release issue - you shouldn't be grinding in any gear with the clutch fully down. I can't remember the last time I had any grinding and I drive my Jeep daily.

The only other possibility is that some sort of misadjustment was done when the new slave went in - maybe they used a spacer when they shouldn't have or something.

The most likely scenario is that the clutch is just really old (maybe even original) and the plate fingers are worn out.

If it were me, I'd replace the clutch. I used a Sachs set which has been very nice, but the Luk set is always a good bet as well. I wanted an all metal TOB which the Sachs had but the Luk did not.
Then, when I was in there, I'd measure the full throw of the arm compared to the full throw of the slave.
I don't recall whether there was a spacer on the slave or not on my 95.
Make sure you lube the input shaft and some folks recommend a new flywheel. Definitely get a new pivot ball and retainer spring for the fork.