Front axle vacuum shift system

[bensjeep]

I have a '90 Wrangler 4.2L and the front axle won't engage. The front driveshaft is powered when I shift into 4wd though. Most of the troubleshooting stuff for the front axle shift motor I've read refers to this unit as having 2 vacuum lines, but mine has three (two ports on the edge of the "pancake" and one on the flat side of it). What does each of these lines do? Also, if I am able to determine the problem is actually the transfer case switch, how is the switch attached? On top the transfer case it seems like there is a little tower with four ports in it, and a rubber manifold that plugs into the top of it. Is this the switch, and how is it attached?[addsig]

	Transfer Case Mounted behind and driven by the vehicle transmission, the transfer case transmits power to the front and rear driveshafts in 4WD Jeep vehicles and offers high and low range.

[Jeepr89]

I had this problem about 9 months ago in my 89 YJ and it turned out that there was a hole in a vacuum line up by the carb. It appeared that sitting over the intake/exhaust manifold it had melted a little bit. I replaced that section of line and it started working like a champ [img]modules/phpBB_14/images/smiles/icon_biggrin.gif[/img] [addsig]

[BigBlackJeep]

If i recall correctly, the lines on the pancake are what engage it back and forth, the third line is just a vacuum line that tells the little 4WD light to come on. I would have a friend engage the axle from inside the Jeep and listen to the lines to if you have any pressure. If not, then just work your way back until you find where you have it. Also, take the carrier off and make sure that it operates freely. My vacuum lines came off the front axle once while hitting a deep puddle hard, the 'pancake' filled with water and wouldn't let it engage. I would check that first to make sure it isn't bound up, it should move freely even with a little bit of lung pressure.



Hope this helps and welcome to the forum



-When the hood of your Jeep is the same height as most passenger cars, thats when you know you have something...-[addsig]

[Bounty__Hunter]

The front axle disonnect is not working properly. It is vacuum controlled, so start by checking the following:

1)Jeep running, in neutral or park with e-brake on

2)Remove the two vacuum lines from the front axle disconnect (on pass. side)

3)Have somebody you trust shift Jeep into 4wd and back to 2wd

4)Feel for strong vacuum in one line in 2wd and other line in 4wd



If that checks out okay, the problem is in the front axle. Remove the shift motor (held to axle with 4 bolts) and work the shift fork back and forth by hand. Clean with WD40 and spray into both vacuum ports while moving the shift fork. Reassemble and hook up the vacuum lines. It SHOULD work now.



If the vacuum check is not okay, either the vacuum switch in the transfer case is bad or there is no vacuum to the transfer case from the intake manifold. The vacuum switch in the transfer case is easy to replace, it threads into the transfer case on the pass. side.



Let me know what you find, I'll help as best I can.



[addsig]

	Transfer Case Mounted behind and driven by the vehicle transmission, the transfer case transmits power to the front and rear driveshafts in 4WD Jeep vehicles and offers high and low range.

	Front Axle Disconnect A mechanical or vacuum-operated component used primarily on four-wheel-drive models to connect and disconnect drive torque to the front axle. When shifting from four-wheel drive to two-wheel drive, this system disengages the front axle from the front driveline, so that the front wheels aren't turning the front driveline unnecessarily. This reduces unnecessary front driveline wear, noise and fuel consumption.

[jeeperwilly]

Bens,



I too have gone through the pains of trying to find the problem in the vacuum system. Mine turned out to be the switch, which was easily replaced after ended up replacing the axel disconnect motor. But here's the thing. The entire system can be replaced so that the only thing you have to rely on is good ole human power. 4x4 Posi-Lock makes a cable controlled replacement for the vacuum motor. It involves replaceing the motor with a cable controlled box and eliminating the vacuum. This also can allow you to put your jeep in 2wd low. Anywho, just an idea if ya want to head down that road. Oh, the sell the conversions a www.4wd.com. Hope ya find the problem, Paul [img]modules/phpBB_14/images/smiles/icon_rolleyes.gif[/img] [addsig]

[Bounty__Hunter]

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font class="pn-sub">Quote:</font><HR></TD></TR><TR><TD><FONT class="pn-sub"><BLOCKQUOTE>Bens,

The entire system can be replaced so that the only thing you have to rely on is good ole human power. 4x4 Posi-Lock makes a cable controlled replacement for the vacuum motor. It involves replaceing the motor with a cable controlled box and eliminating the vacuum. This also can allow you to put your jeep in 2wd low. </BLOCKQUOTE></FONT></TD></TR><TR><TD><HR></TD></TR></TABLE>



Or you can do the same thing with a manual vacuum switch from an SJ, for about $20 or less. IF the vacuum shift motor in the front axle still works good. Then you can weld the front diff for the ultimate in traction [img]modules/phpBB_14/images/smiles/icon_biggrin.gif[/img] [addsig]