The 4WD in my '95 S10 is not working. I know the vacuum actuator is working. I tested it today. For whatever reason, vacuum is not reaching it to activate it.

I believe that newer trucks use a vacuum switch with a solenoid or whatever to activate the actuator.

My idea is to buy one of those, run a vacuum line from a T fitting on the line from the manifold to the switch and from the switch to the actuator. I would install a switch to power the vacuum switch when needed.

Would this work? If so, would I need to even use the 4HI button on the dash?

Pressing the 4LO switch shifts the transfer case, but of course, there is no front wheel drive.

When did they switch the style of vacuum switch?

Thanks.

 

You would still need to hit 4hi to engage the transfer case. The solenoid setup would only lock the front axle in (think of it like locking in the hubs on a solid axle truck), not shift the t-case from 2wd to 4wd.

It seems like it would work, to me. It's similar to the cable "posi-lock" setup that myself and others on here use.

 

I've been doing some more reading and have come up with a couple of wrinkles.

On is, that the vacuum solenoids have only 2 hose connectors. Vacuum in and vacuum out - no vent. Will the vacuum actuator disengage without a vent line? I figure there is a vent somewhere, because newer vehicles use vacuum solenoids and their actuators disengage.

"Encoder failure: Transfer case will not enter 4HI, but will enter 4LO. This is because the computer doesn't know exactly what position the case is in, so it just moves to either extreme (2HI or 4LO)"

This is my situation. It WILL go into 4LO, but in no case does the front axle lock in.

I already ordered a vacuum solenoid, but will go out tomorrow to see if there is a TCCM code. I already cleared them, if there were any and cycled the ignition 5 times. That didn't help.

I can't get under the truck properly - too much snow. I jacked it up and got under it last night, but the only wires I could see were the 2 on the cable that comes from the vacuum actuator.

 

I had the same problem with my 99 blazer with auto 4wd option. When i pushed 4lo or hi it would engage the transfer case but not engage the front diff. i have a service 4wd light that comes on when i engage it so i replaced the solenoid that your talking about hoping that was the problem instead of having the codes scanned at the dealerships but that didnt fix the problem... INSTEAD i just bypassed the solenoid but the bad part about that is you have to go out and connect the 2 hoses together then go push 4lo or high. I will eventually get the code checked but till then ill just use that temporary fix till i start using my 4x4 more often.

 

I got my solenoid switch today and managed to find a connector for it. When I feel up to it, I'll hook a direct hose from the T fitting that normally goes to the vacuum switch to the vacuum actuator. If that works - and I assume it will - I'll put the solenoid switch in line. If THAT works, I'll need to get the wire through the firewall to hook up a switch.

I need to have a way to easily turn 4WD on and off. Side roads around here stay slick forever, but the mail roads are usually dry.

 

The problem with your 95 is something to do with the vacuum switch on the transfer case, or the vacuum lines. GM started using the EV, (electro-vacuum) switch in 1999. If this is the switch you're referring to, it has a built in vent. Applying voltage and ground to the switch will send vacuum to the front axle actuator. Remove voltage and the axle actuator will vent to atmosphere.