Backward 4WD Actuator Operation...Any Ideas?

[tkemmett]

Hello All,
I'm just about done reassembling an 04' S10 crew cab 1/2 basket case project I took over from my brother. It was in pieces down to the frame from the firewall forward for almost 3 years. The truck is back on its feet and running again though not on the public roads yet...I've been taking test drives on local small roads to make sure nothing falls off, launches, catches fire, etc. and that it kinda steers ok, and stops...details details.
The problem that has me stumped and asking all of you for help is the four-wheel drive actuator pod is operating backwards. When two wheel High range is selected on the dashboard, vacuum is being supplied to the actuator pod which retracts and pulls on the cable to engage the differential. When I select the 4-wheel High mode, vacuum to the actuator pod is shut off and the cable is released. Backasswards.
Of the many S10 vac /4WD problems I found searching forums for a solution, I didn't find any posts/threads with the backward operation problem.
I have read about everything I can find and still have no idea why the actuator pod would get vac in 2 wheel drive and no vac at the pod in 4WD. Not having worked on this type of vac actuation before doesn't help. The vac switch (GM), actuator cable, and lines are new.I have double checked that the vac lines are properly connected to the ports on the vac switch at the T-case.
I must have assembled something wrong because the four-wheel drive was working as designed before he took it apart. Where in the pathway from dash switch to the actuator could an incorrect assembly cause the "backwardness"?
I sure would appreciate any info or ideas on solving this... Thanks in advance.

[okaussiee]

The vacuum switch that sits on top of the transfer case is what switches vacuum to the front axle actuator . The connector to this switch is KEYED. If it is put on the transfer case incorrectly, ( it is real easy to do), the vacuum from the source would go to the front axle actuator in 2WD. There are some pics around here that show the connector of which I speak and it will show you the key and the its mate to the transfer case switch.

I had a tranny guy replace my tranny and when he put the vacuum switch connector back on, he put it on backwards and I, too had this problem.

It is hard to see up there but there is good info around here in finding it, and fixing it..

Good luck///

Bill

[tkemmett]

Thank you so much for the reply. I have been hoping someone might have had a similar problem...and then fixed it!
I thought I had keyed the coupling carefully. I sure have learned a lot from the postings you mentioned and thought I had this properly assembled. The vac switch in the case is not indexed in some way is it? I will be able to look at the project later today. Thanks again for your response.

[okaussiee]

The vacuum switch itself only goes in one way. It screws in. It has three nipples on the top with the key. The trick is to connect the hose connector to the transfer case switch so that the key on the switch goes into the hole on the hose connector. It is easily misaligned and causes this issue.

If the right front wheel "locks " in 2hi then "unlocks" in any of the 4WD positions, that proves the connector is misaligned with the switch.
You can also check this by using a vacuum gauge and putting it on the hose in place of the Front axle Actuator. If you have vacuum in 2 Hi and none on the 4WD side then the vacuum switch is miskeyed. If you have Vacuum on any of the 4WD and none on 2HI, then we need to be looking elsewhere.

Good luck

Bill