95 YJ grinding noise (2WD to 4HI while moving)

[TheBigDirty]

Haven't had problem until this winter. Was always able to shift from 2wd to 4h while moving (under 60kmph of course). Super useful as I live in a snowy area. This year when I go to shift there is a grinding noise and I can feel reverberation in the 4x4 shifter. It does still shift but I really have to force it - been avoiding it. It shifts fine from 4h to 2wd.

I suspect the linkage is off but why would it have randomly started causing an issue? I have a 3" BDS leaf lift (previous owner put it in) but have owned this jeep for a decade without issue. Confused. Any ideas?

 

[Flyer58]

I guess I should read my owners manual. I didn't know you could shift into 4wd while moving.

I dint have the need in Houston.

 

[TRevs]

I read that it is acceptable for my LJ, and it still made me tense as heck the first few times I did it.

@TheBigDirty : when did you last change your t-case and differential fluids? Also, have you tried shifting into 4H while driving in mph? It works fine for us south of the border.

 

[machoheadgames]

I would think something is either up with the synchro in the transfer case or the vacuum actuated central axle disconnect on the front axle.

When you are in 2WD, the front driveshaft does not spin due to the CAD. As such, when you shift on the fly, the transfer case has to immediately get the front driveshaft up to speed, which it uses a brass synchro for just like a manual transmission. After that, the front/central axle disconnect vacuum motor receives vacuum and moves a fork over to engage the right side axle shaft.

My guess is the grinding might be from a bad transfer case synchro, but I don’t really know for sure. It could be grinding from something in the front axle. Maybe the fork isn’t engaging properly.

 

[machoheadgames]

I read that it is acceptable for my LJ, and it still made me tense as heck the first few times I did it.

@TheBigDirty : when did you last change your t-case and differential fluids? Also, have you tried shifting into 4H while driving in mph? It works fine for us south of the border.

Nothing to be tense about really, especially in a TJ platform. Since the front diff is live those the front driveshaft is always spinning and ready to go. Makes shifting the transfer case basically completely painless. The YJ is a bit more involved. Still same process for the driver, but the transfer case has a bit more work to do to get the driveshaft up to speed and then provide vacuum to engage the front axle.

 

[TRevs]

I’ve hardly put the YJ in 4wd in the year + that I’ve owned it since it’s just a city driver at the moment, but someday I might take it to Colorado and pair it with the LJ on the trails. Ive thought about doing the CAD delete, but haven’t seriously looked into it since there are higher priority tasks.

Would that help the OP?

 

[machoheadgames]

Hard to directly answer if a one-piece axle shaft swap would help the OP or not. Would be better to dig in and find what went wrong. I’d start at the CAD and then crack open the transfer case. It’s probably in the transfer case.

The CAD setup in stock form is actually very reliable. I didn’t have a single problem ever until I lifted mine and then the vacuum hoses barely reached anymore. They didn’t reach if you drooped the axle fully. I probably should have freed up the harness some for that, it’s clipped to the frame and I probably could have undone that for some slack.

The worst part about the CAD is that the the connection between the inner and outer shaft likes to wear as does the plastic bushing supporting the inner shaft. After a while if that happens, those two will take out the outer axle shaft seal just outboard of the CAD. So you see a lot of front YJ axles with leaky passenger sides.

1-piece is a solid swap, but it often presents vibrations from the front driveshaft spinning full time. Not always, and being stock height helps a lot. The seal needed for the 1-piece can be a bit weird. It’s a simple hammer in oil seal that fits the tube ID. You have to hammer it to the right depth or else it won’t ride on the smooth part of the shaft. You could theoretically hammer it all the way down the tube until it hit the CAD wall. So some figuring out has to be used for proper install depth. On the bright side, if you had any leaks, you could double or triple them up since the tube doesn’t care how many seals are in place.

 

[Gilaguy23]

I guess I should read my owners manual. I didn't know you could shift into 4wd while moving.

I dint have the need in Houston.

2wd to 4wd hi ONLY while moving up to 55mph or something like that. DO NOT try to shift onto low 4x4 unless your barely moving,like 1mph, and preferably stopped completely.

 

[DOWNS]

Most likey the syncro is going out as Macho mentioned. CAD is easy to check for now. Once they went to the 1piece axleshafts from the factory the syncro was deleted from the t-case. I can also shift on the fly into 4H with my CJ2A with front drive flanges, and when I had my CJ5 I would leave the hubs locked in if I knew I would on and off the dirt and shift that on the fly as well.

 

[TheBigDirty]

I read that it is acceptable for my LJ, and it still made me tense as heck the first few times I did it.

@TheBigDirty : when did you last change your t-case and differential fluids? Also, have you tried shifting into 4H while driving in mph? It works fine for us south of the border.

LOL. Maybe I should change me speedo to MPH and try again.

T case fluid changed... in 2018 or so but it's been sitting down in AZ for the past 6 years not doing much. Maybe the desert dried it right out. Will check.

@machoheadgames thanks. I'll take a look at the CAD (not really sure what to look for but google exists) and open the tcase. It's -25 degrees here now so gonna be a spring endeavor. Pretty much exclusively drive in 4x4 hi with all the snow we good anyway.

​

 

[TheBigDirty]

Most likey the syncro is going out as Macho mentioned. CAD is easy to check for now. Once they went to the 1piece axleshafts from the factory the syncro was deleted from the t-case. I can also shift on the fly into 4H with my CJ2A with front drive flanges, and when I had my CJ5 I would leave the hubs locked in if I knew I would on and off the dirt and shift that on the fly as well.

So what specifically would I be looking for if the CAD has failed? I definitely have a CAD (and it was working last winter).

Would getting rid of the CAD and installing a Posi Lock be worth doing? Guess that wouldn't solve my problem if the issue is in the transfer case itself. Flushing fluid/re filling did nothing. I am suspecting synchro or otherwise in the t case.

 

[DOWNS]

So what specifically would I be looking for if the CAD has failed? I definitely have a CAD (and it was working last winter).

Would getting rid of the CAD and installing a Posi Lock be worth doing? Guess that wouldn't solve my problem if the issue is in the transfer case itself. Flushing fluid/re filling did nothing. I am suspecting synchro or otherwise in the t case.

Typically, it's just a failed vacuum line or a line that popped loose somewhere, especially if you're lifted the vacuum harness that connects at the front axle will pop loose. Overall, the system is very simple with not a lot of stuff to fail.

To me, it's not worth going posi lock just because the system is so easy to make it work properly. I mean the posi lock in this case would be a bandaid fix for what might be wrong in the t-case.

On the plus side, the Transfer case is probably the simplest piece of the drivetrain to overhaul. I had mine out overhauled and back in the Jeep (XJ) in about 6 or 7 total hours, not counting dry time on the sealant.

 

[TheBigDirty]

I would think something is either up with the synchro in the transfer case or the vacuum actuated central axle disconnect on the front axle.

When you are in 2WD, the front driveshaft does not spin due to the CAD. As such, when you shift on the fly, the transfer case has to immediately get the front driveshaft up to speed, which it uses a brass synchro for just like a manual transmission. After that, the front/central axle disconnect vacuum motor receives vacuum and moves a fork over to engage the right side axle shaft.

My guess is the grinding might be from a bad transfer case synchro, but I don’t really know for sure. It could be grinding from something in the front axle. Maybe the fork isn’t engaging properly.

It was indeed a bad synchro and shift yoke. I took it out and ordered a rebuilt kit from rigid axle but after watching some YouTube realized I was in over my head and had it rebuilt by a shop. Im fine with the maintenance and bolt ons but gears scare me.

 

[TheBigDirty]

I read that it is acceptable for my LJ, and it still made me tense as heck the first few times I did it.

@TheBigDirty : when did you last change your t-case and differential fluids? Also, have you tried shifting into 4H while driving in mph? It works fine for us south of the border.

Tcase was 1/4 quart of grey goo. Unfortunately refilling did nothing. Shift yoke and synchro were damaged. Had to rebuild the tcase but not it works like a dream.