vacuum lines on 90 YJ

[mountainman]

1046580

I am having difficulty engaging the front axle. I found out that the problem was broken vacuum lines that went from the transfer case to the front axle. So, after a while of trying to patch lines together, and finding problems with vacuum sources and too much to list, I am curious if any of you have vacuum diagrams that you could post or send to me for a 90 YJ with a 258 6 cylinder. A friend of mine gave me his vacuum harness for the front axle because he had just recently swapped out and put dana 60's in. The problem, is that it came out of a 91 which had the 4.0. Any help would be greatly appreciated.



Thanks,

Chip

mountainman_1969@yahoo.com



Oh yeah, I have only owned this jeep for about a month, so I am new to the world of Jeep, well, Wranglers, that is.



Thanks again.[addsig]

 

[Bounty__Hunter]

1046643

[addsig]

 

[Tug-n-pull]

1046659

Dang BH your quick as a switch! That is a great little drawing you got there! Hey Mountianman welcome and I hope that Bounty Hunter has shown you justr what kind of great folk hang out around here. What part of the world are from? Later Tug[addsig]

 

[MORGSTER]

1046692

To understand how the system works might help to repair it.

On the dash is a light that tells you when you are in 4wd.

Under the battery (Passenger side) is a vacuum operated switch for the 4wd light (One wire to ground the other to the dash 4wd light).

The shift motor is where all of the vacuum hoses attach on the front axle.

From there to the drivers wheel (USA) is the long axle and to the passenger wheel is the short axle.

Inside the shift motor is a coupler that when engaged connects them both to be one axle.

On the shift motor there are three connections.

One vacuum line engages the coupler, and at the same time another sends vacuum to the switch under the battery to ground the 4wd dash light.

The third is to disengage the coupler and at that time the vacuum is cut off the ground to the dash light switch, which turns off the light.



Bounty Hunter’s diagram is pretty simple, and so is the system. If it's hooked up correctly, it usually works (Unless their is another problem)



Things that can be bad are.

1. Inside the shift motor, the coupler is broken or it isn't installed correctly)(I find installation is usually the problem)

2.The vacuum lines are incorrectly routed or broken (Note: the colored plastic lines are very brittle with age. One leak and it won't work)(The Jeep will also run ruff)

3.The vacuum/light switch under the battery isn't grounded to the firewall correctly or it's broken (Usually it's loose and not grounded)

4. The dash light is not working (Bad bulb or wiring) (Usually it's the bulb)

Note: The wiring is simple. When vacuum is applied to the switch it connects the two wires inside and allows ground to the 4wd light (It lights up)



[addsig]

 

[Bounty__Hunter]

1046696

Morgster, don't forget that the YJ changed the 4wd light setup from a vacuum operated switch on the firewall to a plunger switch on the front axle disconnect. When the shift fork locks the two axle shafts together, it depresses a plunger that sends an electrical signal from the front axle to the dash light, activating the light. If the light is not on in newer YJ's, the shift fork is not moving in the front axle.



Best way to test the vacuum at the front axle, have somebody shift the transfer case from 2wd to 4wd and back while you feel for vacuum in the two lines at the front axle. Shoud be strong vacuum in one line for 2wd and the other for 4wd. If it checks out, the problem is in the shift motor bolted to the front axle (4bolts). Remove and work the shift fork by hand while spraying down with WD40. Spray in the vacuum ports real good too.[addsig]

 

[MORGSTER]

1046717

BH:

Thanks for the update.

It was so long ago my info is from our 1989 YJ 4.2. (plunger/vacuum switch)(Dana 30)

I have since changed to the Posi-Lok, which uses the plunger/electrical switch on the axle.

This is how we fix our Jeeps...Mass input.

[addsig]

 

[BDurrant]

Red hose with the T from the dana 30 front end. Where does the vaccum source come from? I know it's the carb but where on the carb? and how should it be routed through the storage cannister?