4x4 Not Locking In?

[kawaboy13]

I'm new here, with a question. When you put thos Jeep into 4 wheel drive, the front isn't pulling. It's not making weird noises and you can tell when you put it into low and all. But the front isn't pulling. I'm going to look more at it tomorrow. Could it be the actuator or a vacuum hose? Anything common? Any ever had this problem? Any help would be appreciated as I am wanting to purchase this 87 Comanche. Thanks

[Justin_k]

Probably your Central axle disconnect. Are all vaccuum lines hooked up? easy thing to do is pop the cover and see what's going on inside. Try manually sliding it to the right, and then test the 4x4.

[XJGPER]

If you don't want to get greasy (ha its a jeep and the whole thing leaks). jack the front end up and spin the front shaft, you should get some movement at the tires. If not, apply vacuum to the CAD ports one by one and see if you can get it to move manually. Or do what was posted above.

 

Its a fairly simple system with only 3 points of failure.

 

1. the CAD itself (either the vacuum actuator or a broken shift fork, if its a broke fork make sure to get a later model cast steel replacement, older style is Aluminum).

2. the vacuum switch on the tcase (i have had 2 XJ's have the rubber adapter that slides on the plastic vacuum switch harden and not make a complete seal)

3. Vacuum lines (they are made of the awesomest most britle material known to man, there are 4 different colored lines, 1 is a supply the others are engage / disengage / and 4wd light). If you find a broken line sleeve the plastic line in two layers of heat shrink tube, i've done this numerous times and have yet to have it fail.

 

Good luck!

[Pete M]

viewtopic.php?f=9&t=18415

[kawaboy13]

The shaft is spinning when it is in 4 wheel drive, but the tires aren't getting power. Also my 4x4 light is on. I did find a blue line with a connecter (i guess this is what you'd call it) for another line to run onto it. And down by my actuator there is a yellow, green, and white running out and up. Well I'm guessing these are the same lines, but the white one ends under the hood and does not enter the cab. Is it supposed to be connected to the blue? Is this the engage? Also is the actuator supposed to move slightly like in a spinning motion? And where should I like under the hood for the end of vacuum lines? I really have no idea what I'm doing. Thanks!

[Pete M]

follow the instructions in that link and you'll never have to worry about it again. :thumbsup:

[kawaboy13]

Well if i slide this over, won't it put excessive wear on all the front end? Because it was made with vaccuum lines for a reason. I know it'll still have 2wd and 4wd but the front will always be connected and won't exactly be "free wheeling".

[mvusse]

The vacuum disconnect was a futile attempt to get better fuel mileage. Due to too many problems with it they did away with (in 91?).

 

I noticed no measurable increase in fuel consumption after swapping in a stronger single piece shaft, essentially the same as locking the CAD.

 

With the axle engaged the ring and pinion gears will spin, while the spiders gears hardly do. With the axle disengaged the ring and pinion gears do not spin, but the spider gears will spin like mad. As long as the oil is clean and up to level neither of those should wear out no matter what.

 

The drive shaft will spin, though, causing more wear on the u joints. But how often have people needed to replace u joints on the rear drive shaft that spins all the time? Okay, I admit, I replace u joints all the time, but I abuse my truck off road monthly and with my daughter driving it spends probably 10 miles or more (5+ hours) submerged up to or past the doors in water or mud each month.

[kawaboy13]

So the front drive shaft will spin when it is only in 2wd if I lock the CAD?

[Eagle]

So the front drive shaft will spin when it is only in 2wd if I lock the CAD?

Yes.

 

As already commented above, that does not hurt anything. Starting in 1991 the Cherokee and Comanche did not use the disconnect, so by locking it in the engaged position you are effectively making your front axle the functional equivalent of the newer models.

[Pete M]

you may notice a vibration when in 2wd if any of your driveshaft u-joints are toast. which is sorta a good thing, since then you'll know you need to replace them. :yes:

[kawaboy13]

So when the transfer case is engaged, the shaft turns. Therefore if the shaft is turning from me locking the CAD, wouldn't the transfer case be turning and wearing? Or is there a connection point in there that won't turn unless you engage it?

[mvusse]

Yes, the front output shaft of the transfer case will be spinning with the drive shaft, but there's no load on it, and the transfer case has an oil pump driven by the rear output shaft, so it's all good.

 

Locking the front axle will make it behave exactly like any 91 or newer the way it came from the factory.

[kawaboy13]

So the front and rear turn always on a 91 or newer? So the front only turns when its rolling if I do this? But doesn't have its own power until I put it in 4wd right?

[Bounty Hunter]

The blue vacuum line is a vent, shouldn't be connected to anything.

 

You can also remove the vacuum disconnect from the axle, slide the collar into the locked position. Reinstall the disconnect upside down and it will hold the collar in the locked position.

 

The vacuum setup isn't bad if you learn how to troubleshoot it.

[Eagle]

So the front and rear turn always on a 91 or newer? So the front only turns when its rolling if I do this? But doesn't have its own power until I put it in 4wd right?

Yes, that is correct. Locking the collar will result in your front end functioning EXACTLY like every 1991 and newer XJ and MJ -- as well as EVERY XJ that had SelectTrac (they didn't use the axle disconnect, ever).

[mvusse]

So the front and rear turn always on a 91 or newer? So the front only turns when its rolling if I do this? But doesn't have its own power until I put it in 4wd right?

 

Correct on all three counts.

[mvusse]

The vacuum setup isn't bad if you learn how to troubleshoot it.

 

I got rid of mine for two reasons:

1 - I got tired of the vacuum lines getting snagged and pulled off when off road. Happened three times on two trips.

2 - Axles with the larger/stronger u-joints.

 

Regarding number 2, I had been told that the larger u joints were available in a disconnect shaft from a 95 and 95 only YJ. Not true. The 95 YJ does use the larger u joints. It does not have a vacuum disconnect axle like the 87 through 94 ones do, though. Then 96 does not exist, and 97 - 06 is the TJ, also without a disconnect axle.

[Bounty Hunter]

The 95 YJ does use the larger u joints. It does not have a vacuum disconnect axle like the 87 through 94 ones do, though.

Wrong. My '95 YJ and every '95 YJ I've worked on has the front axle disconnect.

[mvusse]

I know of only one 95 YJ personally, and it does not. Owner says that's the original axle.

 

Not the first time I've been wrong. Probably won't be the last either.

[kawaboy13]

Should I be expecting any troubles? What's the easiest way to slide it over? And once the oil pours out, what oil do I use to add more and how do I check it and where do I add it? I just want it to go as easy as it as said and want to go into it knowing exactly what needs to be done. Also Will the fork sit up against the part I slide over or does it go into it where the groove is?

 

And other than those questions, basically I take out 4 bolts, slide the fork and the ?CAD? over, put the circlip back in and put 4 bolts back in?

[Eagle]

The link Pete gave you in post #4 tells you EVERYTHING you need to know.

[Bounty Hunter]

You don't need to do anything to the c-clip, simply install the disconnect upside down and the fork will be on the correct side to hold the collar in the locked position.

 

If the collar doesn't slide over the splines easily, turn the steering wheel one way or the other to get the axleshaft to turn slightly, lining up the splines.

[kawaboy13]

Do I need to take pressure off the wheels of the truck? Do I need to put it up on jack stands or can I just drive it up on some car ramps?

[Pete M]

as long as it's in 2wd, you can do it anyway you'd like. :thumbsup: if the splines aren't perfectly aligned, you can simply rotate the front driveshaft to turn the inner shaft.