I'm a dummy.

Location
Utah county
I've had this 1990 XJ 24 hours and discovered 4x4 doesn't work. The transfer case engages but when knocked on the front diff no one was home. I just want to confirm this would be a Dana 30? Any specific junk yards good for jeep parts?
 

BlueWolfFab

Running Behind
Location
Eagle Mountain
I've had this 1990 XJ 24 hours and discovered 4x4 doesn't work. The transfer case engages but when knocked on the front diff no one was home. I just want to confirm this would be a Dana 30? Any specific junk yards good for jeep parts?

Your front axle is "vacuum disconnect" meaning the long-side (passenger side) axle is 2 pieces and it has a sliding coupler that essentially engages the two pieces of the axle shaft. That's how it's supposed to work anyways. Without the coupler sliding over to engage the two pieces of the shaft to act as one, all your front-axle driving power is being lost in your spider gears.

You can either fix whatever is causing the failure of the vacuum to actuate on this coupler, either vacuum lines that have came undone, or a bad vacuum ball, or maybe something else (do all your heater positions work? Face, floor etc, or is it stuck on defrost?) Or you can permanently bypass the vacuum disconnect function a number of ways, one of which is replacing the passenger side axle with a one-piece shaft like that out of a TJ Wrangler or you can also modify the shift-fork that actuates the disconnect coupler. In the past I have just modified the shift fork and then the 4wd works perfectly

By fixing the vacuum problem, your front axle would work like factory, meaning your front driveshaft wouldn't be turning while driving in 2wd, helps save an almost-negligible amount of fuel.

Or if you bypass the vacuum disconnect function your front driveshaft would turn while driving when in 2wd no matter what, it wouldn't have "power" to it from the drivetrain, but would turn because your front wheels are turning and without the vacuum disconnect all the power from the front wheels turning gets transferred all the way up to the front driveshaft.
 
Location
Utah county
Seems to me the simplest will be in the drive shaft. I mostly drive around town so mpg isn't a big deal. Would it cause additional wear on anything on a longer highway drive?
 
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BlueWolfFab

Running Behind
Location
Eagle Mountain
Seems to me the simplest will be in the drive shaft. I mostly drive around town so mpg isn't a big deal. Would it cause additional wear on anything on a longer highway drive?

No not really, just make sure your Ujoints are greased and in good condition. It's actually better for your spider gears that way.

Should the front drive shaft spine quite freely in 2wd? I understand with an open diff, and one axle disengaged it will spin free, I just wonder how freely.

Yep quite freely.
 

Bart

Registered User
Location
Arm Utah
Pretty sure the 90 XJs do not have a vacuum disco. You can tell if there is a box like thing on the passenger side tube. I know neither my 88 nor 91 had one.
 
Location
Utah county
I'm in Payson. Looked at a 4Wheeler magazine article on it. I'm thinking I could drill a hole on the housing opposite the vacuum plunger, and run an all thread bolt all the way through, with a nut inside to hold the fork in place, and then just seal up the holes on the outside to prevent moisture.
I'm Payson
 

BlueWolfFab

Running Behind
Location
Eagle Mountain
On my last one I flipped the shift fork inside the housing and then installed the housing upside down and that held the collar right where it needs to be. Free, quick and effective. Just some basic hand tools.
 

BlueWolfFab

Running Behind
Location
Eagle Mountain
Yeah the shift fork has a dogleg in it, so when you flip it it moves it over a lot, (too much) so flipping the housing puts it back where it needs to go. Granted it was 10 years ago that I did it so I'm running off of memory here, but 94% sure that's how it went.
 
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