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My YJ is behaving like it has locking hubs...

3K views 12 replies 5 participants last post by  jhendry 
#1 ·
Being new to Jeeps and 4x4 it didn’t seem strange to me that the front drive shaft spins freely while I’m under the car (it’s not on jacks) and it’s in 2H. After thinking about it for a while, though, that didn’t seem right. That mean the front wheels aren’t engaging when I change into 4H / 4L.

What am I missing?


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#2 ·
It’s normal, the front axles are independent, when you engage 4x4 they “connect”. There’s a vacuum motor that does this, should be in the passenger side of the axle. If you engage 4x4 you shouldn’t be able to spin the front drive shaft freely.


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#3 ·
What Yjalex said is true. I'll add to that.
If you're stock vacuum activated Central Axle Disconnect (CAD) is functioning properly the Jeep has to be running to activate it when you shift your transfer case into 4H or 4L. Without the vacuum to activate the CAD, nothing happens except you won't be able to turn the driveshaft with the transmission in gear.
Why they call it Central Axle Disconnect is a mystery to me when it's off on the passenger side of the axle.

When I mention "if your stock CAD is functioning properly" I mean to say there are other aftermarket modifications that will activate the CAD without the engine running.
Some Jeepers feel a manually controlled cable is more reliable. This is a point of discussion that pops up regularly. I have the stock setup on my Jeep and the Jeep is 33 years with close to 200K miles. It still functions as designed.

If you have any questions on how to know if your 4WD is engaging feel free to post again.

Good Luck, L.M.
 
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#4 ·
Thanks guys! that helps a lot. I'm not sure the front axles are engaging when I go into 4H. I suppose the only way to check that is to jack it up? My 4x4 gauge doesn't light but that could be just electrical. Any other suggestions on troubleshooting?
 
#5 ·
On '94 YJs the 4X4 light is lit with a switch on the CAD housing. OP's issue could be as simple as a burned out bulb or a bad connection.
On earlier YJs the 4X4 light is lit by a vacuum operated switch mounted on the firewall, near the battery box.

Good Luck, L.M.
 
#6 ·
You need to get the Jeep safely in the air with all four wheels off of the ground. Then check that the front axle is engaging when you shift in to 4wd. If the driveshaft turns but your wheels do not then you axle is not engaging. This is usually a vacuum issue to the actuator on the passenger side of the axle. You can trace down the vacuum to try to find the problem or replace the actuator with a cable actuator or a kit to permanently lock the axle.
 
#8 ·
Just a thought. Is your jeep totally stock? I'm asking this because mine acted like it had a 'Locker' in the front when my mechanic installed a Detroit TrueTrac in the front axle. he had used the wrong oil. I took it back and handed him the correct oil and it has worked perfectly since.
 
#9 ·
My Jeep is mostly stock except for the lift, 31" rubber and a couple of small things like the airbox has been replaced with those individual cold air intakes, which I don't really like. I'm going to get it onto a lift and check if the vacuum lock is engaging. Is it worth opening it up and at least cleaning it out & putting new oil in? I'm pretty sure the TC is engaging so I think I'm going to start there & work backwards.
 
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#11 ·
Took me about 5 minutes to find that most of the vacuum lines are wasted away! I’m looking for the replacement harness but the connector on the lock motor doesn’t look right. I’m really sure my 94 YJ has got the stock CAD.

Anyone got a part number?


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#12 ·
Google "Summit Racing". Enter "vacuum harness" in the search box.

They show several. Pick one that will work for you.

Good luck, L.M.
 
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#13 ·
LuckyMac, I’ve spent 2 hours scouring all the sites I know (including anything else google can find). I can see a couple of used ones from DeadJeeps but the new ones seem to be the same price. The closest I can get is the Crown 53001100 but I can see that the connection to the Disconnect Motor is wrong. Anyone else know the part number for the 94 YJ??


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