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vaccuum axle disconnect problem, will not disengage front axle


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After my engine swap I have not been able to disengage the front axle. It wouldn't be a problem except that the front pinion bearing is wailing like a banshee at 40+mph. I seem to have a vacuum problem. The linkage disengages 4wd and shifts perfectly, but the vacuum signal is not being changed from the back of the TC- I'm still getting a vacuum in the line that holds the front axle engaged and there is no vacuum on the line that is supposed to disengage. I cannot find any kinks or breaks in the vacuum lines. I have all the EGR vacuum lines plugged and bypassed. The truck's idle hunts a little bit but generally stays around 500-600rpm. 

In order to drive it without the wailing banshee noise I pulled the actuator off the axle, manually shifted the sleeve over to disengage the axle, put it back together, and left the vacuum lines disengaged. If I hook the lines back up it shifts the sleeve back over. 

With the lines disconnected, I still get the 'part time' light except for when I press on the gas which I assume take vacuum pressure away and make the light go out. 

 

Any thoughts on this? Is there a vacuum switch that goes out on the transfer case that sends the signal to one side or the other that I can replace? I don't want to spend much money on this (such as replacing the VAC with a cable [~$200] or buying a new actuator[$80]) because I have mid term plans to replace the driveline with one from a newer cherokee. I would, however, like to have a working 4wd system without having to take the cover off and manually slide the sleeve over. 

 

Thanks

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not sure how the AX-15 swap affects this.  :dunno:    the real problem is that pinion bearing.  the temporary solution is getting the CAD to work properly.  is it possible the lines are switched?

 

 

 

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not sure how the AX-15 swap affects this. :dunno: the real problem is that pinion bearing. the temporary solution is getting the CAD to work properly. is it possible the lines are switched?

 

 

 

I said that because the newer transfer cases like the one I swapped in to my jeep during my ax15 swap, doesn't use the vacuum system

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Pull the front drive shaft, until you find a more permanent solution? Or, REPLACE/FIX the bad bearing (or whatever is failing).. if that is really what is wrong. 

 

With the fork shifted over and the 2-piece shaft "engaged" is no different than running a non-Cad axle.

There is some WRONG. 

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thank you for all the comments. I believe my lines are routed correctly because a: I didn't disconnect them during the engine swap, etc. and b. the part time light is on which tells me it should be the CAD should be engaged as it is. 

 

after doing some simple google searches, I see that the vacuum switch is simple and a cheap $10 part so I've ordered that. While I was doing the engine swap I was fighting off a lot of dirt dobber nests so it's possible something could have got into the switch while it was sitting disconnected. 

 

I agree the CAD bypass would solve the problem but it would force me to deal with the pinion bearing and, for the kind of money it would cost to have that rebuilt, I could get a late model XJ front end. I've seen a few good deals on front+rear ends but I'm not ready to tackle the project of welding perches and mating brake lines, etc. 

 

While I wait on a new vaccum switch I just have the vacuum lines disconnected from the axle actuator and the axle collar shifted manually to 2WD. 

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I got a front axle from a late xj with the same gearing as my mj. $150.

Direct swap. Front alignment when done. No worries.

Thanks. Unfortunately I have 3.07 gears so if I attempt a swap I want to go up to at least 3.55. I had a line on a great set of front+rear axles a couple weeks ago that was an hour drive away but my slave died and took the truck out of commission.

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I swapped in a new $10 vacuum switch in the back of the TC and the 4wd shifts flawlessly. Back when it did work it took forever to shift out of 4wd with lots of backing up and pulling forward. Now its nearly seamless. I still have issue of the front pinion bearing and the fact I'd like to swap axles for better gearing for bigger tires but I will probably put that off until next year and enjoy that my truck is, more or less, fully functional.

Thanks again for all the advice.

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glad to hear it was something simple. :thumbsup:

Likewise.

 

Simple is good. :)

 

Thanks. Simple is good; cheap is better. Simple and cheap is the unicorn of jeep problem solutions. I would not have guessed that simple little vacuum switch would go out.

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