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Vacuum Actuator - Newbie

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20K views 11 replies 5 participants last post by  Mean Max  
L
#1 ·
Ok...2nd day Jeep owner here and I realize today that my 4WD isn't working. Front drive shaft does turn in 4WD. So that leads me to believe that I have a vacuum problem or that the actuator itself is bad.

I tried to test the vacuum by running the vehicle in neutral and checking the hoses that I removed from the actuator. There doesn't seem to be any vacuum from either hose. Does vehicle need to be in gear?

Also, what is the electrical connection on the fork housing for? Is there some sensor in there to signal on the dash that I'm in 4WD?
 
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#2 ·
linusb said:
Ok...2nd day Jeep owner here and I realize today that my 4WD isn't working. Front drive shaft does turn in 4WD. So that leads me to believe that I have a vacuum problem or that the actuator itself is bad.
You're on the right track, IMO.

I tried to test the vacuum by running the vehicle in neutral and checking the hoses that I removed from the actuator. There doesn't seem to be any vacuum from either hose. Does vehicle need to be in gear?
You should always find vacuum at one of the hoses at the actuator. You either have a cracked/broken line between the switch (on the T-case) or between the T-case switch & the manifold. Only the T-case needs to be engaged, it makes no difference whether the transmission is in gear or not.

Also, what is the electrical connection on the fork housing for? Is there some sensor in there to signal on the dash that I'm in 4WD?
Not a sensor, but a switch. The rod for the shift fork operates the switch that turns the 4WD dash light on/off.
Click to expand...
Here's more from the YJ Tech FAQ section.

http://www.jeepforum.com/forum/f12/...f12/frequently-asked-questions-faq-your-answers-usually-here-451154/#post445405

Image

Max :cheers2:
 
R
#3 ·
hahaha welcome to my world.
park neutral it doesnt matter.
sometimes the small black hard plastic line cracks and you lose everything. or the vacuum bottle. do yj's even have vacuum bottles? ( im an xj guy same front axle tho)
yes the electrical is to tell you that it moved and your in 4
you got a few options
buy a non vacuum operated passenger side axle shaft.
buy a posilock worst money i ever spent broke first time out.
take apart the shifter mechanism move the c clips around permanently lock it
take it all apart weld it locked
buy a new one for like $100
 
L
#4 ·
Ok, so I'm going to try and trace the vacuum hoses.

There is a large skid plate/bracket under the transfer case. I started taking it off so as to get better access to the transfer case and it seems that it's supporting a lot of weight. Is it ok to remove that??? Seems like it'll be a bear to get back on?
 
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#5 ·
linusb said:
Ok, so I'm going to try and trace the vacuum hoses.

There is a large skid plate/bracket under the transfer case. I started taking it off so as to get better access to the transfer case and it seems that it's supporting a lot of weight. Is it ok to remove that??? Seems like it'll be a bear to get back on?
Click to expand...
Not without supporting the transmission or transfer case!

The skid plate IS the crossmember!

Notice the jackstand supporting the transfer case at the rear.

Image

Here you can see the vacuum switch on the driver's side of the transfer case. It has the 4 black vacuum ports on it.

Image

Max :cheers2:
 
#6 ·
Not necessary to take anything off. The vacuum switch is on the back end of the transfer case on the driver's side. It has a four-opening rubber connection for the vacuum lines. This should just slip on/off.
 
M
#7 ·
If you have a manual trans, you can remove the shifter boot, and the cover plate that is under it(I would assume that the auto's would have the same plate, but I've never had an auto, so I'm not 100% sure). once you remove that plate, you can access the top of the T-case, and the vacuum switch. Looking down from the top, the vacuum switch will be on the drivers side of the T-case, and slightly to the rear of the hole in the floor.
 
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L
#8 ·
Wow! You guys are great! I may have screwed up then because I released one whole side of that support bracket and the whole thing dropped several inches. (i did this before I posted my question). After I itial panic I got the jack and raised everything back into place and bolted it. I was able to shift through the gears after starting it but haven't taken it completely for a drive. How likely am I to have damaged something?
 
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#9 ·
I doubt you damaged anything. None of the linkage (except automatic tranny linkage) is body mounted, so it would have all moved with the driveline. It wouldn't hurt to chect your engine & transmission mounts though.

Max :cheers2:
 
#10 ·
Take a minute to completely fill out your profile. That way we'll know whether you have an auto, manual, etc.

Max :cheers2:
 
L
#11 ·
Phew...that is a relief. Thanks again! I do have a manual. And that picture helps a great deal. I do in fact see the switch now on my Jeep. I can't quite tell, does that switch come off? How does that switch work...some mechanical valving in the transfer case when the front drive shaft is engaged?

Also, I see what is either the check valve coming up into the engine bay which is routed with the vacuum supply line from the manifold. I imagine if the check valve is failed that could be the source of my problem? The hoses themselves seem to be in pretty good shape though I've not pulled them from the switch to find the vacuum source and to see if vacuum is actually getting to the switch.
 
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#12 ·
linusb said:
Phew...that is a relief. Thanks again! I do have a manual. And that picture helps a great deal. I do in fact see the switch now on my Jeep. I can't quite tell, does that switch come off? How does that switch work...some mechanical valving in the transfer case when the front drive shaft is engaged?

Also, I see what is either the check valve coming up into the engine bay which is routed with the vacuum supply line from the manifold. I imagine if the check valve is failed that could be the source of my problem? The hoses themselves seem to be in pretty good shape though I've not pulled them from the switch to find the vacuum source and to see if vacuum is actually getting to the switch.
Click to expand...
Here's the routing of the 4 lines from the switch.

One vac line runs from the intake manifold to the T-case switch. It has a one-way check valve in the line to maintain vacuum during wide-open-throttle. This line provides the vacuum to the system.

Another line runs to the shift motor/actuator on the front axle. This line provides vacuum (designated by the T-case switch) to the shift motor to keep the axle disconnected in 2WD mode.

The other line to the shift motor/actuator provides vacuum to the shift motor to keep the axle engaged in 4WD mode.

The last line goes up the firewall to a breather cap. This is the "vent line" where the switch can dump the vacuum that is no longer needed from the shift motor/actuator when it switches from one mode to the other.

The vacuum switch is operated/activated by the internal shift linkage of the transfer case.

Hope this helps! :thumbsup:

Max :cheers2:
 
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