2004 Blazer, 3 Button on the dash.

After reading many different threads on here, and gaining a lot of knowledge on the issue, I still cant solve my 4x4 issue.

The problem started about a month ago.. While driving at 60+ MPH a "whirring" sounds would come from the front end. Clicking into 4WD would cause the sound to disappear completely. From other threads I found out what to check and the classic problems:

I replaced the transfer case vacuum switch on the transfer case. Mine is the 2 prong, it seems like most have a 3 prong?

I removed the battery and battery tray with the car running, and inspected the vacuum actuator, which looks good. The actuator cable moves freely the inch or so it should. When someone engaged 4WD in the car so I could watch, nothing moved around the actuator. A clicking sound could be heard inside the dash, and the light switched from 2WD to 4WD.

With the car off, I squeezed the vacuum actuator and I could hear the hiss of air near the firewall, which leads me to assume there's a bad vacuum cable. If there's a vacuum leak, wouldn't the 4WD not engage, unlike what I'm experiencing? I traced a hose from vacuum actuator towards the firewall, but couldn't find where it actually goes. Any help there?

Where I'm confused is why shifting into 4WD while I'm driving is stopping the sound or having any effect at all. If the vacuum actuator isn't moving as it should, what is changing that stops the sound? This leads me to think there's more than one issue. My HVAC system is working fine.

Thanks for any help, I realize theres hundreds of threads dealing with similar issues, but I'm still at a loss.

 

The problem is the axle clutch is partially engaging when you're in 2WD causing the noise. Selecting 4WD fully engages the axle clutch and the noise stops.

This thread might help: https://blazerforum.com/forum/2nd-ge...working-75064/

 

Usually this is caused by the vacuum switch sticking open and allowing constant vacuum to the actuator under the battery tray. If you've replaced the vacuum switch and have the vacuum lines attached correctly, this should not be happening. Your vacuum switch should look like this:



I've never heard of a 2-prong switch for the t-case...sure you got the right one?

 

Is there any chance you have a switch that looks like this attached to the firewall above the distributor? It should have 2 vacuum lines and one electrical connector with two wires in it.

 

I'm sorry, that is the one I bought and installed. I was thinking about a different fix I recently finished which was two prong. I did however forget to mention that the ball on the end of the old switch was indeed stuck pressed in. There seemed to be a small amount of liquid (oil?) around the old switch. After installing the new switch and going for a drive I can still hear a humming sound coming from the front end which goes away with 4WD engagement.

With the new switch installed and car running, I pulled the battery and battery tray and again had someone press the 4WD button inside, and again a sound can be heard (It seems louder and like something is actually happening?) but the actuator is not moving at all.

I'm not seeing that.. But that also reminds me. I can still hear a air hissing sound from behind the motor/near the firewall while depressing the actuator.

Thanks for the link, I read through the thread once but will have to read through it again. What I still think is interesting is that the actuator isn't moving at all when 4WD is selected, yet the axle clutch wants to engage for a different reason?

 

When the vacuum switch fails, it can suck fluid from the transfer case into the lines. If that happens, it will cause the actuator to operate, (in both directions) very slowly, if at all. Remove the transfer case oil fill plug, if fluid runs out, that's probably what happened. All of the vacuum lines, and the actuator under the battery, all need to be cleaned out.

EDIT: Follow the vacuum line from the actuator to the vacuum switch and look for cracks or leaks.

 

Quick aside as I'm currently under the car.. How flush should the 3 piece vacuum cable be to the switch? I'm 99% sure I have it lined up correctly with the keys on both ends..

 

Yup, looks good. There is a locator tab on the plug and on the switch, make sure they're lined up. No oil in the lines?

 

As of this second I'm trying to pull the fill plug to see if any fluid comes out, but I'm having troubles finding it.. (embarassing). Everything I've read says the plugs should be removed with sockets, but all I can find in are these two which would need hex keys.. Are these the plugs?

Edit: Photo should be rotated 90 degrees clockwise..

 

The upper one is the fill, lower is the drain. Fluid level should be at the bottom of the fill hole.