Well, I don't know where to begin, but I will try to summarize. I have a 1998 S10 Chevy Blazer in good condition. It has 115,000 miles on it and it is well maintained. But my issue is simply maddening! I have had several varied 4WD issues ranging from the transfers case vacuum switch, to the encoder motor, to the vacuum actuator, cable and switch. Essentially I have replaced ALL of them and i still have an issue. I have no lights on the 3 button 4WD push button switch, and when stopped and in park if I push the 4HI button they (4HI/4LO) both blink several times and go out. I jacked up all four tires and repeated the process, and the same thing - but here is the funny thing that happened: If I pushed the 4Hi switch the front tires would not turn, and the lights flashed as above. When I pushed the 4LO button, the encoder motor functions, and I'm in low range 4WD (verified by actually driving it - it was low range and the steering wheel would pulse while turning on gravel). Great. So I jacked it back up, repeated the above and pushed the 4HI button (encoder functioned, lights blinked) and the front wheels started turning, but eventually stopped - I did nothing to make that happen, other than watch the front tires stop turning.

I have replaced every 4WD component - all of them just to start fresh. Very expensive indeed!

I checked the vacuum and it maintains 17 inches idling and with the motor turned off.

It acts like something is engaging partially, then disengaging. I hear no noise. No relay sounds. No clunking or other metallic sounds.

I have had to replace the lifetime encoder motor as the first one was brand new and in-op. the second one seems to work, but I think it is disengaging somehow. Does that seem likely? Any thoughts?

Again I have replaced the 4WD switch, relay in the passenger kick panel, encoder motor, vacuum actuator, linkage, transfer case vacuum switch, and verified I have vacuum - please help.

Parson Brown

 

So do you have the 3-button transfer case? This is the one that doesn't have the Auto-4wd.

You wrote a lot but I'm not quite sure the issue. Is it that you only seem to get into 4wd when you select it using the buttons on the dash when you have the front tires off the ground? Or is it that you only have 4wd when you are in 4Lo?

You say you checked the vacuum with the engine off. Where did you tap into the vacuum lines?