Front Axle Not engaging.

[Aspirated]

Need some suggestions on where to start, my front axle doesnt seem to engage. First diagnostic steps?
Its a 91 Wrangler.

[JackstandJohnny]

Central Axle Disconnect.
is you 4x4 light on?

[justchillinout]

A problem that I had was with the vacuum control switch on the trasfer case and the check valve.



I would also check your vacuum lines for cracks or breaks.  I've had one line come off.

Start with the vacuum system then start checking the actual engagement at the axle.

[cLAY]

You'll go nuts trying to keep that vacuum system running on an older Jeep. I nearly did.

Just pull the vacuum motor out of the backside of the front diff. Play around with it a bit, slide it back and forth so you understand how it works. Then remove the c clip holding the pot onto the housing. Disassemble the unit and stack washers next to the fork so it stays in the 4wd position, reassemble and install back into the diff. You front diff will now always be locked in and the front drive shaft will always spin. This is NOT a problem(unless you have a big lift) as this is the way all the newer Jeeps are made and as soon as you pull that lever connected to teh t-case for 4wd you WILL have 4wd EVERY time.

[hps4evr]

check the shift fork in your front CAD system. its made of aluminium and they are prone to cracking and breaking. do what clay said or get a posi-lock system for it with a cast iron fork.

[Aspirated]

Thanks for the tips. This will be this weekends project.

[Aspirated]

Ok, so.
 Fork in the front diff is moving to the side. I have 4wd when lifted on a hoist but it seems to "pop" out when on the road under load. From what i seen of that fork it cant jump over without braking so i'm going to assume its a t-case issue. Is there an adjustment on the t-case?

[justchillinout]

I'm not really sure this is it, but did you check you vacuum backflow valve?  If it is not holding the vacuum in, the fork may be allowed to release.  Just a thought.

[WagoneerXJ]

I used the washer method on my old 90 XJ, and never looked back.

[cLAY]

Its not the t-case its the vac disconnect in the axle. The system works fine when jacked up because the engine is sitting at idle, this is when there is the most vacuum available. When you are driving the amount of vacuum you have diminishes as you give it more throttle. At WOT you don't have any manifold vacuum available for accessories such as the 4wd system.Does the heater also stop blowing thru vent and switch to defrost and then back again when you let off the throttle?

To compensate for this a vacuum reservoir was added. This works fine as long as the system is 100% with zero leaks. Any little leak and the reservoir runs out and then the fork slips back into 2wd. You would think that once the fork was slid over into 4wd it would stay there on its own but its doesn't. Without the vacuum motor constantly pushing on it the fork will slid back to 2wd.

Like I said I went crazy trying to fix mine. It would work fine on stands and just driving around, easy trail riding, no problems. Hit the first tough obstacle, give it some gas and BANG!, sounded like the t-case chain jumped and then no front drive. Back down check things out, all good, try obstacle again and BANG! same thing.

Eventually I just shimmed the fork and never worried about it again. Later I found that my vacuum reservoir had a crack in it and wasn't holding vacuum.

[Aspirated]

My jeep had a line cable added by the previous owner, after fiddeling with it for a cpl hours i just dropped a tack weld on the coller, lol. Theres enought room to get a grinder on it to get that stub out when required.

Now, what about front axle upgrades? I have stock gear up there now, best to just add a locker?

[hps4evr]

go find a hi pinion 30 from a cherokee, hack all the coil mounts off, add some leaf mounts and you'll save your self a lot of grief down the road.

[Aspirated]

There are a cpl options with the HP Dana 30 it seems.  My understanding is some have full time engagement, eliminating the need for the vacuum or cable actuated egagement system. Is there a particular one that works best?

[WagoneerXJ]

91 and up XJ's/zj's and later TJ's do not have this vacuum junk. ALL YJ's and 84-90 XJ/MJ's do. Get an axle from one of the newer ones, cut the mounts off and weld your old ones to it