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Np242 slips into fulltime 4wd

X

xjdavid1

NAXJA Forum User
Location
Brisbane Australia
I have a 1995 xj cherokee with 4l motor np242 tc 4.5" re lift and it is jumping into fulltime 4wd when i am in 1st gear low range from time to time. I happens when it gets bounced around. I dont know if is because the tc is worn or maybe the gearbox is moving around and pulling on the linkages to the tc.
 
Are you saying its shifting from part-time low into full-time? That would require it to go all the way through neutral too which seems kind of remarkable

Maybe its slipping into Neutral instead? Neutral uses the "full time" position on the indicator switch, but you would notice the sudden loss of traction

Or are you in part-time high and its falling into full-time?
 
Last edited:
When in 1st gear low range i am losing rear drive. I think the only way this could happen is if the centre diff lock becomes unlocked and all the drive goes out the front.
 
It sounds like your linkage is out of adjustment, and things are moving around such that it pops into neutral. How do your transmission and motor mounts look? That can be enough to do it.
 
Agreed, probably falling out of Part-Time Low into Neutral, and probably because the linkage is out of adjustment. If the handle stops moving before the shift completes, it can fall back out when the jeep jumps around. There should still be some pull/bend in the handle all the way back and all the way forward, and then check the z gate at N and FT to make sure you aren't throwing all the way through either of those positions either. http://www.boostwerksengineering.com/242-HD-Shift-Linkage-Auto-Trans-_p_27.html makes it easy but I don't know about shipping to Aus
 
I have adjusted the linkage and it made no difference. I have replaced all the bushes in the linkage. The 4wd light is flickering . Seems like the center diff is unlocking sometimes.
 
the center diff can't unlock in low range. The fork is way past that section.
if the 4wd light is flickering then it's coming out of 4 lo. The sensor for the light hits detents inside the case. The only way it flickers is if the linkage is moving, or there's something way wrong inside your case.

since you say it happens when you're bouncing around, I'd suspect the drivetrain is moving significantly and pulling the linkage. What's your motor/trans mounts look like?
 
The differential requires substantial shift collar movement to disengage, probably over 3/8 of an inch of movement.

IMG_20150913_144939.jpg


The bottom part of the outer shaft I am holding is the section that the part-time/full-time collar rides on. There's lots of travel, so falling out of gear would be... difficult.

If it did fall, the bang of the abrupt shift would likely jar the whole Jeep. Here is a picture of a 242 gear train for reference.

IMG_20150906_231314.jpg


A quick tour - On the left-most side we have the low range differential, then the speed shift fork, followed by the 4wd mode selector fork, then the differential, followed by the front drive gear, and finally the oil pump. The teeth on the front bit are the mode selector's detents. They are fairly substantial. When you shift, do you feel them? There is a ball tensioned spring that I suppose if the spring was broken would allow movement.
 
I have had similar trouble with my 242 and no matter how I adjusted it, it would always just slip out of low. I replaced motor mounts (Brown Dog) and the tranny mount, but no help. So I took off the center console and used a dremel to cut back the last gate position by about 1/4-3/8". Problem hasn't come back since. I think that since the 242 uses the full throw of the gating mechanism that it is very sensitive to the linkage adjustment being absolutely perfect. Increasing the distance of the rear gate solves that issue.
 
the_weirdo said:
I think that since the 242 uses the full throw of the gating mechanism that it is very sensitive to the linkage adjustment being absolutely perfect. Increasing the distance of the rear gate solves that issue.
Click to expand...

This makes sense, I cut at least 1/2" out of mine now that you mention it. I can take pictures if you need. I have replaced my linkage with the boostwerks setup which helps, but I don't know if that's an option for you.
 
I've had my TC (231) start jumping out of 4low, so Ditto on above checking the rear trans mount. Don't just visually check it. Put a bar next to it and see if you can shift the trans back and forth. Put some umph into it :). The mount may be good, but you might have lost one or more of the upper bolts.
 
Just had a closer look at the transmission mount and discovered that is cracked quiet badly. Took me by susprise as it is only a few years old. I have ordered another non genuine one as i cant find a genuine one.
 
xjdavid1 said:
Just had a closer look at the transmission mount and discovered that is cracked quiet badly. Took me by susprise as it is only a few years old. I have ordered another non genuine one as i cant find a genuine one.
Click to expand...

:clap: Good deal. Get that replaced and then re-adjust your linkage again and you should be good to go (hopefully :cheers:)
 
xjdavid1 said:
Just had a closer look at the transmission mount and discovered that is cracked quiet badly. Took me by susprise as it is only a few years old. I have ordered another non genuine one as i cant find a genuine one.
Click to expand...

plan on doing the motor mounts too.

if they're weak you'll kill another trans mount in short order.
maybe take the opportunity to upgrade to some brown dog style units.
 
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