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Old 01-19-2014, 03:49 PM   #1
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Broken 4wd :(

So, my jeep is a 1989 4 cylinder, 2.5 liter. currently I cannot get my front axle to lock into 4wd. For a while I couldn't move my 4wd shifter at all, but the other day I was getting pulled out of some snow, being jerked around quite a bit, and I could shift again (still not being able to engage though).

I hate to say, when I opened the drain plug, there was hardly any fluid in it. I put in a good 2qts of ATF.

I have the jeeps front end lifted off the ground, shift in both 4hi, and 4low. Only one tire spins. And the driveshaft to the differential is not spinning.

When it is shifted into 4low, it acts like it's engaged (drives very slow, low rpms, etc) just doesn't engage my axles.

I think that's about all the info I can share about my problem, any other info I'm missing, just ask, does anyone have any ideas? Do I need a new t case? Should that vacuum motor mod fix my problem? Any and all help will be appreciated much.

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Old 01-19-2014, 04:33 PM   #2
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Make sure you have vacuum to the disconnect on your front axle and that it is working properly. If it is working then it is something in your transfer case. (Probably a worn shift fork based on your problems, which is fixable.)

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Old 01-19-2014, 07:27 PM   #3
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X-2 sounds like your front axle disconnect isnt working. Now would be a great time to eliminate the CAD and install a Posi-Lock
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Old 01-20-2014, 01:02 PM   #4
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So your "cad" (now even sure what that stands for, is controlled by vacuum. There are 3 spots for vacuum. 2 are a sucking, one is a pushing. Correct? Sorry, I'm only a beginning tech so I don't know everything quite yet... Lol.
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Old 01-20-2014, 03:29 PM   #5
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It stands for center axle disconnect and what it does is split the front end so the separated tire side has no traction (just a spinning shaft) which effectively places the jeep into 2-wheel drive. I don't know about your transfer case so I don't have an answer, but most transfer cases, when in 4-hi or 4-lo should spin the front driveshaft with the engine/transmission regardless of whether a CAD is present or not. The CAD will prevent either tire from turning the driveshaft though until it is activated and locks the split into one shaft and then it will act like a normal open diff unless you have a limited slip or a locker engaged.

Certainly don't know much about your setup, but maybe this helps a little
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Old 01-20-2014, 06:28 PM   #6
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Quote:
Originally Posted by RandomYJguy View Post
So your "cad" (now even sure what that stands for, is controlled by vacuum. There are 3 spots for vacuum. 2 are a sucking, one is a pushing. Correct? Sorry, I'm only a beginning tech so I don't know everything quite yet... Lol.
The CAD should only have two vacuum lines going to it that switch sucking and pushing when going from two to four wheel drive.
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Old 01-20-2014, 09:27 PM   #7
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I did away with my vac also. I did a cable. If you are handy with a welder or can braze, there is a demo on utube. I did that one. Total cost was about $40.00. When I need 4x4 I need it, I don't need to be playing find the vac leak. Now it works everytime, on time.
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Old 01-20-2014, 09:46 PM   #8
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Wow. Thank you for the info, that's a lot of info!

So Wednesday I think I am going to try and do this mod, see if that will fix my problem. Sounds like it's more a vacuum issue.

How hard is it to replace the transfer case? Or rebuild one?
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Old 01-21-2014, 05:20 AM   #9
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Depending on how good you are with a wrench removing and rebuilding the transfer case is not awful (I'm still in high school and recently did mine). And replacement it would be more expensive but easier if you don't want to tear it apart. First be positive that your vacuum is working before you go taking things off
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Old 01-24-2014, 10:39 PM   #10
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It's strange that the front drive shaft won't turn when you shift into 4wd. If that's the case, it could possibly be as simple as shifter linkage adjustment. If the linage is ok, then your problem is in the transfer case. I recently changed the chain in the t-case of my '93. Same as yours, there was virtually no fluid in it. There are several videos on YouTube on how to remove the np231j transfer case. I would highly recommend a set of gear wrenches. There's 3 out of 6 nuts that the t-case is secured to the tranny with that can not be reached by ratchet. Splitting the case while it is on the vehicle is very easy. I used this video for guidance, but watch several just for referance:



Hope this helps, and good luck!
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Old 01-24-2014, 11:10 PM   #11
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[QUOTE=RandomYJguy;7563033
I have the jeeps front end lifted off the ground, shift in both 4hi, and 4low. Only one tire spins. And the driveshaft to the differential is not spinning.

When it is shifted into 4low, it acts like it's engaged (drives very slow, low rpms, etc) just doesn't engage my axles.
[/QUOTE]

The problem is most likely in your CAD. or the vacuum lines in between there and the t-case.

The drive shaft will only spin when you are moving...jacking the front up off the ground and putting it in 4wd will not tell you anything without putting power to the shaft by putting the trans in gear, which will drive it off of the jack. Its an open differential, so turning a tire wont turn the driveshaft. The reason is cause you are turning the drivers side axle which is spinning the spider gears, if the CAD was connected and working, and you spun the drivers side tire, the passenger side tire would spin in the opposite direction. Then you know the 4WD is engaged and the CAD is working.

Vacuum lines on the t-case...red is the vac. line coming from the motor, green is the vac. line going to CAD to engage 4WD, yellow is the vac. line going to the CAD to disengage 4WD and blue is the vac. line that releases the pressure so that the vac. can be switched from green to yellow.

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