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Discussion Starter · #1 ·
I recently bought a 1987 Jeep Wrangler with a 4.2 liter 6. Comming from the transmission, there are four color coded hard plastic vacuum lines. They are coded red, green, yellow and blue. These vacuum lines pass under the battery, on the passenger side, and appear to go to the front axel shift motor.

Close to the front passenger wheel (still inside the engine compartment) these four lines have splices in them. The yellow and green line are spliced color to color and are connected to the front axel shift motor. The red and blue lines are disconnected at the splices. The problem is, there isn't a red and blue line connecting to the shift motor. There is instead another yellow line and a black one. In essence, on the transmission side of the splices, the colors are red, yellow, green and blue. On the axel shift motor side of the splices, they are yellow, yellow, green and black.

Does anyone know what is the purpose of these lines, how they work, how they should be connected, what the vacuum source is? Also, because of the difference in colors, is there a component missing?

Also, from the transmission, there are two other ordinary black rubber lines. These go up and are just attached to the firewall with a plastic clamp. Both of these hoses have a white plastic cap in the end of them. Any ideas of what these are for???

Thanks ahead of time for any help.
Thom
 

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(Moved to YJ tech. chat)

YJs will have several vacuum lines coming in and out of the transfer case (which sits behind the transmission). One will be coming from the engine intake manifold, and will be Teed in with a vacuum canister. Two will go to the front axle - where they engage and disengage a fork that connects the passenger side axle shaft to the differential, this device is known as the CAD.

As for the rubber lines, one of them is probably a breather. Thats all I know for know - YJs aren't my specialty, but I've worked on a few and those are the ones I remember.
 

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Discussion Starter · #4 ·
vacuum lines.

Thanks. Yes this looks like the vacuum lines on the engine. But, I don't see the four lines that attach to the transfer case, and the four that attach to the vacuum switch on the front axel.

most of the vacuum lines on the engine I will probably disconnect, because this is going to be an off-road application, but the four wheel drive will not engage without these four connected. So, I just need to find out for certain how these four lines connect.
 

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Ah I see. Try this and tell me if this helps. I may have more info somewhere if this doesn't help. I think this will help you though. Let us know.
 

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The posting in blue is some information I found in my saved folders. I only know that the original author is named Bryan. That's the best I can do to credit the original author. The text matches up well with the diagram that I have posted. This should be pretty useful along with the diagram. I knew I had more info somewhere. Let me know if this helps you.

The vacuum lines for the 4wd axle disconnect system always seem to get unhooked, melted, or ripped totally off. Here is a way to check to see if everything is hooked up right, and if it isn't, how to hook it up the right way.

On top of your transfer case will be four nozzles that control your front disconnect system for your 4wheel drive.

The red line coming from your transfer case is the hose for the vacuum source(constant). That will hook up to a hose running behind your air cleaner, if it is still there. Take a look and you will probably find the remains or the original red line. If you don’t have the remains of the original line that is hooked to the constant vaccuum source, find a port on your intake manifold that has a constant vaccuum(or ports on your carb).

Take apart the plastic housing around the vacuum harness(don't break it) to see the lines. Connect what seems to match up for now. Your best bet is to cough up the $30 that a new vacuum harness costs at the dealer and install that instead of driving yourself insane with broken lines.


(blue line) Leave hanging, it has a check valve on it which gets hooked to nothing.
(red line) Hooks up to a good constant vacuum source off of the manifold.
(green line) goes to the shift motor on the front axle. Horizontal on the shift motor.
(black soft vacuum hose) goes to the plug on your firewall by the battery for the 4wd indicator on the dash.
(yellow line) goes straight to the shift motor; one of the lines that goes into a two line plug verticle on the shift motor.
(black hard line) goes with one of the yellows to the shift motor. Plug located vertically on top.
 

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Hacks off Parts while Lit
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well...i got the vacuum fixed to the cad. the vac source was disconnected.......BUT....still no joy. im guessing the CAD is trashed. do yall have a good (i.e. cheap) source for a CAD or is a posi-lock the way to go?
 

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I think Collins Brothers is the cheapest I have seen for the PosiLock. They had it for $159. I have heard of people building their own versions of the PosiLock, But I have not looked into that option much.
 

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whoa, sweet!. thats 40 bucks cheaper than ive seen it so far. what do u suppose are the odds that if i open up the cad i could free it up or something? or do u think the diaphram in there or whatever is prob pooched? i plan on opening it up this weekend, b/c im hopefully gonna change the gear oil and check out the internals
 

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I have heard that the vacuum switch on the transfer case is prone to fail. I am not an expert on the subject, but it is something cheap to try. Have you checked to see if you have vacuum at the lines that go into the CAD? That would at least let you know if the vacuum switch is working.
 

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Xfer case switch...

i can't get the 91 wrangler to move in 4/w drive.
Does the vacume acuator on the front axle have anything to do with this?
I do not have a rear drive shaft at this time, having a new one made.
If the front axle is moving when in 4h or 4L but the jeep does not, does that mean that the axle's are not engaged?

Is there a indicator in the dash board?
 

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This is probably your problem, your vaccum pump has failed on your actuator. Read this article, and see if this manuel replacement is what you need to get your front axle working again. I would imagine that this will fix your problem.

https://www.quadratec.com/products/52435_01.htm

I thought I had posted a picture of this manuel actuator somewhere else on this forum, but can't find it. Just go to the link, and it will all be transparent.........lol.
 

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the indicator works off of vacuum coming from the CAD. first, see if ur driveshaft is turning. if it is, the problem is the CAD. remove the vac lines at the CAD with the engine running (brake set). u should feel vacuum on one side when in 2wd and on the other side when in 4wd.

if you do not feel vacuum, follow those lines back to the top of the t-case and make sure theyre not broken, punctured, kinked, etc.

if u DO feel vacuum, remove the CAD (a little gear oil will spill) and again, start the engine and shift from 4wd to 2wd, you should see the fork move from one side to the other. on mine, the prob was the vacuum lines, sometimes the diaphram in the CAD dies. if its dead, either buy a new one, buy a posi-lock, or if ur a tightwad broke redneck like me, build urself one :D

edit: sorry blu, we musta been typing at the same time. wasnt trying to "outdo you" :p
 

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just checked for vacume lines, guess what it's all electric, from the front axle to the t/case. So the 91 is all electric or the vacume goes to a switch at the T/case.
So is there a swich in the dash or is it all automatic.?

What does the acuator on the front axle do?

need your advice?
 

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amara8 said:
just checked for vacume lines, guess what it's all electric, from the front axle to the t/case. So the 91 is all electric or the vacume goes to a switch at the T/case.
So is there a swich in the dash or is it all automatic.?

What does the acuator on the front axle do?

need your advice?
the vacuum lines come from the top of the tcase. i have never heard of or seen one thats electric. did u pull one of the lines off the CAD? i think you'll find its vacuum...

The CAD slides a collar that connects the outside axle shaft to the inside shaft, when theyre disconnected, the spider gears in the diff make it so if its not engaged, ur not going anywhere.

check it again.....there should be three vacuum connections on the CAD.....
 

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CAD stands for central axle disconnect.

let me know what you figure out

lets see some pics of ur jeep. sounds sweet (you got the best color at least, whether the rest of it is worse a darn or not :flipoff: )
 

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The electric wires go to the left side of the acuator on the front axle. Looks like a cellinoid. The vacume line,2 , go to the other side where the diafram is. I only saw the electric wires because there out in the open and the vacume lines are incased in a plastic hose.

So now I have to trace the vacume line from engine to CAD and I found the the vacume line from cad to front axle.
 

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Ok guys I got the diagram and the instruction from the post, thanks again. Ill let you know when I get my rear drive shaft and also get the 4/w drive working.
Right now it is stored in another place.

Thanks a bunch
 

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amara8 said:
i can't get the 91 wrangler to move in 4/w drive.
Does the vacume acuator on the front axle have anything to do with this?
I do not have a rear drive shaft at this time, having a new one made.
If the front axle is moving when in 4h or 4L but the jeep does not, does that mean that the axle's are not engaged?

Is there a indicator in the dash board?

With the link provided, i most certainly agree with. i used to have a 91 yj and was experincing the same issues. Went straight to the posilok. well worth it man. all cable driven
 
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