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update: Solved. '99 5 spd wrangler loud clicking noise, 4.0L, AX15, 231J

1821 Views 2 Replies 1 Participant Last post by  Salmonfishy
Hello all, i've never posted on these forums but have browsed them several times for other issues or things i was curious about, but this one i just can't figure out.

I've got a noise ive been unable to pin point in my wrangler. its a 99 TJ with the original 4.0 with 90k miles. reverse went out of it on the original ax15, had a few years with a 727 automatic in it but decided to switch back to the 5 speed. just liked it better, and felt like i got around better in the woods. the original 231J output shaft was twisted off in 2015 when the rear axle locked up while driving, and its since had a different 2000 231J. not sure now what that one came out of, but it was working just fine with the 727. The rear axle is an 8.8.

Now to the noise. heres a video of the sound: New video by Jakob Mitchell (hopefully i can post links).
i only hear the noise when coasting, engine disengaged while wheels spinning. seems to be related to vehicle speed, not engine rpm.

here is what i've tried so far:

  1. Installed the (new to me) AX15. it came out of a YJ, but not sure if that is where it originated or not. the tag on top by the shift tower was too worn to read, and the stamped number on the bottom of the case starts with a 5, which i understand to mean its a 1995. it does have the external slave cylinder bell housing. the YJ was donated and all but the transmission has since been sold. Install went smoothly, made sure the input shaft tip matched the pilot bearing 0.75". New pilot bearing, throughout bearing, and clutch. the flywheel is from the original ax15. The only concerning thing was the shifter did not work without bending it backwards, it was hitting on the floor of the jeep when trying to get to first gear. i had a shift tower from a TJ, and it also wouldnt clear without hitting. easy to fix, but not sure why..... On the first road test, all of the gears pull fine and shifted fine, though a slight grind into third. at high speeds between gears (3rd to 4th, 4th to 5th) the noise is heard. same on downshifts, or while the clutch is pressed. if i shift into neutral and coast down the road, it does not matter if the clutch is pressed or not, there is no change in the sound. Since i knew everything else had just been working fine, i assumed there was something wrong inside the transmission and decided to do a complete rebuild when changing the fluid didn't help at all.
  2. when my rebuild kit arrived, i tore down the transmission and saw rust on some of the gears and some pitting starting. by the time i was done, all bearings, both seals, syncros, and every gear aside from the gear on the input shaft were replaced. the cluster shaft was probably okay, but figured what the hell ive already replaced almost everything else. the only things that remain are the input shaft, output shaft, and the 3-4 syncro hub. got it back together, verified the shifts, and stuck it back in the jeep. ..... same sound as before.
  3. We got a wrecked XJ in the back lot, so i took the 231J from it and swapped it into the TJ, at this point thinking it was one of those dumb luck situations where it just decided to go out on me right when i started messing around with the tranny. Nope, makes the exact same noise. FWIW, the XJ was a 99 with a AW4.
  4. running the jeep through the gears with the transfer case in neutral, it does NOT make the noise, everything sounds great.
  5. with the Transfer case in 2wd and the rear driveshaft removed, it does NOT make the noise.
  6. with the transfer case in 4H and the rear driveshaft removed, it DOES make the noise.
  7. 3, 4, 5 & 6 elimates the rear axle, front axle, and both driveshafts from being the source as it happens without them engaged. the transfer case on its own shouldnt be the issue, unless i have really bad luck and the XJ had the same problem.
  8. ...now i'm back to the transmission being the issue, despite being almost entirely new internals.

any ideas what I'm missing?

additional notes:

Looking online, i see there are a bunch of different inpout gears on the 231J. Novac adapt suggests a post '90 AW4 vehicle would have a "medium input" which lead me to think perhaps that was whats wrong if the AX15 should have a "short input" BUT the 2000 231J input gear measures 1.2" out from the mounting face, which indicates it is a short input, and it again has the same issue, so i dont think it has anythign to do with that.

as mentioned mid way though 1, the shifter wasnt lining up in the jeep. The only thing i can come up with that would effect that, would be the bell housing being longer than it should be? ive tried to find if there are alternative bell housings that would fit the AX15 and bolt onto the 4.0L, but seems like the only one that should is the bell housings from a TJ or YJ, and they appear to be the same. i havent figured that one out yet. is it possible i have a Toyota R150 (or something similar) thats essentially the same thing but maybe the length is different? hmmm. it looked like the input shaft had good engagment with the pilot bearing when i pulled it out to rebuild it, but ill have to look again if end up taking it back out.

been fooling with this thing for months, mostly on weekends. have plans to drive it out west late June, but it isn't looking good for me.
I'd appreciate any insight you guys could give me. i know guys that've been messing around with this stuff for 20 years and are just as stumped as i am.
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Update today, narrowed it down a little more.

Realized if i could stop the engine while the wheels were spinning fast enough to make the noise, then i could isolate the transmission input shaft and ALL of the gears inside the transmission by shifting to neutral and disengaging the clutch while the engine was off.

Raised it up on jacks and did just this. here's a video of the process: Sound with Engine Off
What i find interesting here is the sound continues after the input shaft and transmission gears have stopped, and continues until shortly before the wheels stop spinning but NOT the entire time they spin. This eliminates the input shaft, cluster shaft, and all gears inside the transmission. (i suppose the reverse idler could be moving around too, but that would suggest the reverse shift fork is not being locked out by the detent balls like it should be. i do not think this is the case, but will investigate it when i inevitably tear it back down soon...) this also eliminates the pilot bushing, throw-out bearing, clutch, flywheel, engine, everything up front.

what it leaves as the possible problem is the output shaft, or how the transmission and transfer case mate up. i mentioned in my original post my transfer case has the "short input" and that the AX15's want the short input. i looked into this more and sounds like there might have been a changeover year from short to long.... in 1995. Shorts up until 1994, then long after that. this info based on a guy over on another forum. This goes against the table on Novak Adapt, but so does my transfer case from a post '90s AW4 being short instead of medium. along the same lines, the novak site suggests the short-medium-long protrusions from the front mounting face is 1.2" -1.7" - 2.1". Mine, and the two other 231J i have around, measure 1.375" protrusion from the front mounting face. I'm not sure i trust that table very much at this point. I'm wondering if i have a "short" input mated to a long input AX15, but i'm not sure how that would be making the noise or how it would be pulling if it was a problem. ill have to measure the engagement when i start pulling this all back out of the jeep this weekend.

TL;DR --
The clanking noise is related to the transmission output shaft, transfer case(unlikely its been replaced already), or how they are mating up together. The sound is only audible if the jeep is coasting in neutral OR the clutch depressed OR both clutch depressed and in neutral. The sound is noticeable while the engine is engaged ONLY when the driven wheels are floating while on jack-stands. the noise is not noticeable with the transfer case shifted to neutral, or the driveshafts removed. seems like it needs a little bit of loading, but not the full weight of moving the vehicle down the road.

My next steps will be
  1. Repeating my test today but with someone laying under the jeep to listen for the noise when i turn the engine off and its the only thing making noise. they should be able to hear about where its coming from a little better, and maybe feel it on the side of the case.
  2. Removing the transfer case, and measuring the engagement between it and the transmission. inspecting for any obvious interference or problems.
  3. full tear down of the transmission and re-inspection of the shift forks/detent, and the gears/bearings/syhncros on the output shaft and the output shaft itself.

what a headache!
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Well, today I found the problem(s). This weekend I pulled the transmission and swapped it with a known good ax15 before I dug into mine looking for something wrong. Good thing I did, sounded exactly the same.

Today after work I decided to pull the transmission back out, and use the spare clutch, pressure plate, and flywheel just for fun- why not, it's the only thing I haven't replaced.

When I got it out, I noticed the entire pilot bearing and sleeve could be moved around inside the crankshaft with just my finger. WTF?? Pulled it out with a prybar (it was that loose) and it was scarred up on the outside edges. Guess it was a little out of spec? Found a random pilot bearing that fit the Jeep, no idea where it came from or went to but it looked pretty new. Stuck it in, tight fit.

Put everything back together.... Still had the noise.

HOWEVER, I redid my test with just the rear driveshaft and just the front driveshaft, and my rear driveshaft is making a second part of the noise.

So all this time I had two terrible noises masking each other and it took me this long to figure it out. Not sure if I should be happy I'm finally done with it or mad at myself for taking so long. HA!
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