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Old 08-11-2014, 12:26 PM   #1
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93 YJ 4x4 doesnt work

I've seen tons of threads where people have issues with the vac lines going out on their YJ's and then 4x4 doesn't engage and the light doesn't come on. Well I don't know what the cheapest solution to it is, as people have so many ideas. Basically I got stuck in the mud yesterday and realized my front wheels weren't spinning and when I'm in 4x4 my light doesn't come on in the dashboard. What would be the cheapest way to get this working again? Or how can I check my vacuum hoses to see if that's the problem? I'm pretty stumped and don't know what to do.

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Old 08-11-2014, 12:43 PM   #2
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There is a vacuum switch on the top of the rear of the t-case.

4 plastic vacuum lines running into it.

Red is vacuum supply coming from the motor. Yellow is 4wd engaged. Green is 2wd engaged. And blue is vacuum bypass.

It takes vacuum to engage the 4wd and it takes vacuum to disengage the 4wd.

With the motor running (to get vacuum) pull the red line off and make sure you have vacuum in it. Then put it in 4wd with the lever and check that the yellow line has vacuum in it.

If you have vacuum in the yellow line, then the problem is in the CAD, (center axle disconnect) and if no vacuum in the yellow line, the switch needs replaced in the t-case. No vacuum in the red line and you have to follow it up to the vacuum canister to find out if its broke or cracked along the way.

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Old 08-11-2014, 12:53 PM   #3
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Quote:
Originally Posted by 0III0forlife View Post
There is a vacuum switch on the top of the rear of the t-case. 4 plastic vacuum lines running into it. Red is vacuum supply coming from the motor. Yellow is 4wd engaged. Green is 2wd engaged. And blue is vacuum bypass. It takes vacuum to engage the 4wd and it takes vacuum to disengage the 4wd. With the motor running (to get vacuum) pull the red line off and make sure you have vacuum in it. Then put it in 4wd with the lever and check that the yellow line has vacuum in it. If you have vacuum in the yellow line, then the problem is in the CAD, (center axle disconnect) and if no vacuum in the yellow line, the switch needs replaced in the t-case. No vacuum in the red line and you have to follow it up to the vacuum canister to find out if its broke or cracked along the way.
Thank you. Are there any videos that you know of where I can watch someone do this? It's easier for me to watch someone do things than it is to read and figure it out.
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Old 08-24-2014, 01:05 AM   #4
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bump..

I am still bummed and I don't understand exactly what to do. I don't know what the vaccuum switch looks like or is. I looked underneath and could not find it (don't know what to look for).

Also, how do I know if there is vaccuum in the hoses? Do I just put my finger on the hose and see if it is sucking? I am sorry if this is a stupid question. I'm just a young guy and don't have a lot of experience working on cars
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Old 08-24-2014, 01:14 AM   #5
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Actually, I forgot to add. Would it be much easier, simpler, or a better solution to just install a posi-lok cable? I read that you can do this to replace the current vaccuum system because it tends to be faulty and fail. Seriously bummed having a 2wd jeep and ANY input would be appreciated
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Old 08-24-2014, 02:40 AM   #6
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I would just try to fix what you got first.

Down on the back of the front axle is the vacuum motor with a couple of vacuum hoses going to it. With the engine running and secured from rolling over you, feel for vacuum at one of the lines. Then place the transfer case in 4WD. feel for vacuum at the other line. If the vacuum switches, then that vacuum motor needs to come off and see if its just the sliding sleeve that's stuck, or the vacuum diaphragm is bad.



If there is no vacuum at either, next to check is the switch. Mounted on top of the T-case near the front output. Pull the four hose plug and check that vacuum is getting to it.



If taken care of, the vacuum CAD system is just fine. Its just another thing that gets neglected and after 100K+ miles needs a little servicing. When it finally "fails" your typical jeeper "engineer" decides that its junk and antes up for a better mousetrap.

Check yours out. Take the CAD motor off and see how it works and fix it. Its really easy once you see it open. They are easy to find cheap replacement parts for at boneyards off earlier XJs.
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Old 08-24-2014, 03:17 AM   #7
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This is a good video of whats what. The jeep is almost exactly the same as this dodge 2500

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Old 08-24-2014, 04:58 PM   #8
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Figured it out... I followed the hose all the way up to the motor and... it was simply un-plugged. When they did my engine swap, they forgot to plug so much stuff back in. It's ridiculous.

Might I just add that 4x4 is amazing. I got to use it for the first time today and OH MY GOD. So much more helpful hahaha
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Old 08-24-2014, 06:25 PM   #9
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Ta-Da.

Not so bad, was it?
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Old 08-24-2014, 07:29 PM   #10
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Good wright up OIIIO, and good wright up and pics DRED, wow i think I could have fixed Mine with all that! LOL good on ya's

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