i have a 2.8L 1986 s10 blazer, and the 4 wheel drive does not engage. i have needed it twice now, but left stranded twice. where should i start? i select 4wd with the lever and the front wheels do not engage. but i select all the way down to 4 wheel low, and it does change to the lower gearing. but again, the front wheels are not engaging. i purchased the truck a few years ago, and i am not sure of its history. any help is much appreciated..

 

Search is a good place to start. Pretty much all of the s-series trucks have a common front axle activation mechanism. Engine vacuum is routed to the front axle actuator when in a 4wd mode. The actuator then pulls on a cable which pulls on a shift fork that engages the coupling in the front axle.

You need to have engine vacuum to the actuator, the actuator needs to pull on the cable, and the cable needs to pull the shift fork to engage.

 

i have replaced the damaged vacuum line from engine source to the top rear of the transmission, as well as the breather tubes and the return vacuum line to the actuator motor. i notice as i engage 4wd, the vacuum indeed affects the reservoir. but i am not certain how much pull on the cable is required to actuate the fork. from my observations, it "looks" weak. should the reservoir be completely compressed? and how much cable movement is required to actuate? thank you for the reply

 

On the newer trucks, the movement is around half an inch. You could try pulling on the cable with a pair of vice grips and locking it in the pulled position to see if that does the trick...