1994 T100 V6 5 speed manual trans ADD

A few days ago my neighbors retriever trapped a squirrel under my T100. In the process of trying to get it, it ripped all kinds of wires out of place. It even pulled on the speedometer cable and popped the connector off the back of the dash.

Wires and 1 connector was ripped off the side of the transmission and now the front vacuum actuator will not engage the front differential.

My question is how does it work? One sensor is on the transfer case and the other is on the transmission. The one on the transfer case makes sense but what does the one on the transmission do, backup lights? Every part in the system works but the actuator, 4WD in and out and 4WD low. When back in 2WD the shaft out of the transfer case becomes free. The only component which has been knocked out is the vacuum actuator which locks the one side of the axel.

It would seem that the vacuum system is activated by sensors in the transmission and/or transfer case which then sends power to a valve to activate the vacuum system when the transfer case is engaged.

Since I now need 2 new sensors because the wires have been ripped out of one and the connector broken off the other--------- this might be the final staw. I could just install a manual switch to engage vacuum but it would probably be better to deactivate the worthless ADD all together. It has never worked properly when cold. It should have been called the automatic mind of it's own disconnecting differential as it often will only unlock when it feels like it. I once had to drive 50 miles at 40 MPH in lock because it would not free up on a zero degree day. That was what caused me to install manual hubs. I just need to take that stupid ADD system apart and get it fixed into the lock position.

Talk about a stupid system. Manual is always best.

I am looking at a bare bones F250 because it's the only 4WD system with the option of manual engagement and free/lock hubs. If only I could get the F250 with anything but a 12 MPG 6.2L gas monster motor.

What ever happened to simple work trucks?

The switch in the transmission is the reverse switch (triggers backup lights).


ADD cliff notes:

Pulling the t-case shifter to 4wd does two things:
1) manually engages a synchro that first gets the front drive shaft spinning the same speed as the rear and then fully engages it,
2) closes the 4wd switch that triggers the ADD to activate via vacuum switches.
Once the ADD has activated, the switch there is the final link that lights the 4wd indicator on the dash.


The vacuum switches are on the driver's side fender in the engine bay and there is a vacuum reservoir canister in the wheel well/bumper area and then lines going down to the actuator on the diff. Vacuum switch failures are fairly common complaints, as are vacuum lines getting knocked loose, etc.