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Okay this is an XJ questions but found no help elsewhere


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I have an 85 xj. Carbureted 2.5, torqueflight 904 tranny, np207 case.

 

Brief history: an older lady I work with wanted it out of her yard. I went and got it. motor was stuck because it sat for 6 years with the head off due to a blown head gasket that was abandoned mid repair.

 

I put another 2.5 out of another 85 xj in it. Had a vacuum diagram nightmare :mad: , but I have everything working it seems except the 4x4 system.

 

The culprits: There is a blue hose, and a red hose (assuming both are vacuum hoses) that goes under the jeep, I think they go to the top of the transfercase. I cannot tell what the red one does, when I "t'ed" the blue one into the hvac system 4wheel wanted to stay on all the time, which made the tcase makes scarey noises :eek: when the tcase shift lever was in 2 wheel. So I am thinking if I can get the blue and red hose where they are supposed to go that would solve my issues.

 

Thanks in advance: I would just start plugging stuff up in different ways, but the above mentioned situation with the scarey sounds makes me really not want to tear up the tcase.

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There should be three vacuum lines to the transfer case, blue, red and yellow if I recall. One is vacuum supply and then the 4WD selector directs vacuum through eiter one of the others. One to engage the axle and one to disengage. Check to see if the selector still performs that function and then check to see if the part on the axle still works. If either one doesn't, you can always permanently engage the axle. Check the transfer case too. Engage it and see if the front drive shaft rotates.

I don't understand the scary noises. There are two separate events when 4WD is engaged. The vacuum only is involved with connecting the right drive shaft. The transfer case is all internal. If that is making noises, that's a whole other problem.

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There should be three vacuum lines to the transfer case, blue, red and yellow if I recall.

 

Really their are alot going into the top but none of the others have been tampered with during the engine swap.

 

 

One is vacuum supply and then the 4WD selector directs vacuum through eiter one of the others. One to engage the axle and one to disengage. Check to see if the selector still performs that function and then check to see if the part on the axle still works.
Okay I don't know but I think the red one is the supply, where does it attache? intake manifold?

 

If either one doesn't, you can always permanently engage the axle. Check the transfer case too. Engage it and see if the front drive shaft rotates.
Okay so I have to have the vacuum source attached before the front driveshaft can turn at all correct?

 

I don't understand the scary noises. There are two separate events when 4WD is engaged. The vacuum only is involved with connecting the right drive shaft. The transfer case is all internal. If that is making noises, that's a whole other problem.
Well I hope it doesn't have a separate set of issues. When I applied vacuum to the blue hose it made the 4x4 light stay on all the time (and 4wheel was working when the lever was in 4wd((tested it on a slick hill))), even when the lever was in 2wd the 4x4 light stayed on. Now that the blue hose is not attached it no longer makes any noise and the light went off. Some one on another forum I searched said the blue hose was a purge and should not have vaccum on it at all. I don't know if they are correct.
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The vacuum source on my 86 is from the junction for the heater controls which is feed via the reservoir befind the bumper. Usually there is a leak somewhere in that line. Down at the axle you will see three lines, probably blue, white or yellow, and green. It sounds like the axle disconnect is functional. The blue line vacuum engaged it and once it is engage then vacuum is directed to the green line which turns on the indicator light. The other line, white/yellow is used to disengage the axle and hold it. Note, the system is designed to always have vacuum in one or the other line.(oxymoron?) You need to get vacuum to the selector and confirm that it it changes the vacuum route, blue for engage and white/yellow for disengage. If the selector lines are off, with this description you should be able to figure out which one goes where. Under the hood on the right fender, there are some check valves and filters. These probably are functioning but really doesn't affect anything.

No vacuum is required to engage the transfer case to make the front drive shaft to rotate. It's all mechanical. And again the light really only indicates that the axle disconnect as moved to the engaged position and has now directed the vacuum to the light switch.

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Thanks jaekl, this is starting to help me understand...

 

http://www.jeepforum.com/forum/showthread.php?t=642930

 

I found this in a yj forum should this be correct for my application also? If it is it would be a helpful reference.

 

Also it sounds like you are saying that vacuum issue that I am fighting is trying to get the front axle to engage not the tcase correct.? So the tcase should work with or without vacuum.

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The transfer case shifts into and out of 4WD mechanically, by the lever. No vacuum involved. When in 4WD, the transfer case then sends vacuum through a port on the transfer case to a switch on the firewall, which controls the light, and then to the disconnect motor on the axle.

 

What I would do is remove all the vacuum stuff, shim the disconnect to the engaged position, and drive it. The position of the lever will tell you when you're in 4WD. However, you can probably keep the vacuum line to the firewall switch if you want to retain the light, and just eliminate the harness from the switch to the axle disconnect motor.

 

There are write-ups on this site on how to permanently shim the diconnect motor, so I won't repeat.

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Thanks eagle. I will look up the shimming write up if I can't get the vacuum right.

(the red one being manifold vacuum which I do not have connected.)

would this image be correct for what I am doing with the vacuum lines. Rather than shim the motor I might just put a non disconnect front end in, I can usually find them pretty cheap... I am sure there are write ups on them as well. (or are they more trouble than I am foreseeing?) Seems like the same amount of work in my mind, but I could be wrong.

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I converted a dicso front end to a non dicso like 2 weeks ago for a friend of mine. It was as easy as changing oil. I think he got the "kit" from rusty's(like $10). All that was in it was a seal for the pumpkin (to keep gear dope from giong down the tube anymore) and a block off plate. Put a TJ axle in it and no more vaccum problem. Unless you want the light. I can attempt a writeup if it would help.

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Put a TJ axle in it and no more vaccum problem. Unless you want the light. I can attempt a writeup if it would help.

But a TJ axle is a low-pinion D30. You lose the disconnect but you also lose the high-pinion differential.

 

For the amount of work involved in swapping an axle, plus the need then to change the calipers, I would MUCH rather just shim the disconnect and be done with it. If you do that you don't even have to get involved in axle seals. That's only for if you remove the disconnect and replace with a solid axle shaft on the right side.

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I am talking about putting a solid axle in the right side. Using the 1 piece TJ axle shaft and replacing the 2 piece you have. You put a seal in the diff because you don't need anything lubricated down there because the disco stuff is gone.

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That's what I did, except my shaft came out of an ABS Grand Cherokee. The stock seal for a non disco housing won't fit as the passenger side tube inside diameter is smaller on a disco housing.

 

Browse through my build thread for a part number on a seal that works. It is on one of the last few pages.

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I just re-read the original post. First off, if the goal here is just to get a freebie Jeep running, I think suggestions about swapping out axles and so forth are a bit off-topic. The simple solution is just to shim the disconnect. It's free and it takes less than an hour.

 

However, the original question seems to suggest that the disconnect is connected and staying connected, and the OP wants to make it disconnect because he thinks it is harming the transfer case.

 

That would be wrong.

 

Starting in 1991 Jeep eliminated the disconnect front axle in the XJ, but they kept the NP 231 transfer case. The transfer case should shift into 2WD even if the front axle stays connected ... which is why shimming the disconnect to remain permanently connected is a useful work-around for problems with the vacuum shift motor. If the transfer case is making scary noises in 2WD, I would first verify that the noises are from the transfer case, and not perhaps a partially disconnected axle. Second, I would check to verify that the transfer case linkage is adjusted correctly so that with the lever in the 2WD position, the t-case is fully disengaged from the front drive shaft.

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