So I’m kinda new to the whole auto 4wd hubs (I’ve only ever owed manual locking hubs). When I have all 4 tires off of the ground in 2wd hi and I try and spin the driver side front tire by hand it spins the drive shaft, when I spin the passenger front tire it spins nothing because it’s in 2wd. So my question is why is my driver side hub not unlocking or is it supposed to stay locked because I can spin the front drive shaft by hand and it spins nothing because I assume it is sending the power out the passenger side that’s not locked up (02 manual trans with 4 button 4wd)
I have been trying to do research on this and some are saying it’s correct so the drive shaft stays at speed for the auto 4wd but that doesn’t make sense in my mind, thank you anyone in advance

 

What year and type of Blazer do you have? I'll assume you have the S-10 type.

For these, for 4wd there are two things that must happen. First the transfer case is engaged. The second is that the right-side axle shaft in the front axle is locked to the right-side front differential output. This is engaged by a vacuum actuated cable with the vacuum actuator residing under the battery (at least in the 2gen ones). These front differentials are all live, i.e., non-locking, from the factory.

Thus, when in 2Hi, the front differential only sees rotation of the left-front tire, it being disconnected from the input shaft from the transfer case and being disconnected from the right side wheel.

There were two types of transfer cases installed. Colloquially they are called "3-button" and "4-button." The 4-button that you have has the extra button that allows for and Auto-4wd. Selecting this puts the transfer case into a mode where it can shift in and out of engagement on its own depending on the amount of wheel slip it senses.

From what you described, there must be some internal friction such that when turning the left-front wheel, it is the input shaft that rotates instead of the right-side differential output.

I hope this helps.

BTW, a common failure mechanism is that the underhood vacuum lines rot so that there is no vacuum available to engage the front axle. A symptom of low or no vacuum is that the HVAC actuators that direct the air flow will not work or not work well as they are operated by vacuum too.

 

You are correct. For either transfer case, in 2WD Right front wheel should be disengaging and not spinning the driveshaft.

 

A bit more....

You are correct. For either 3-button or 4-button transfer case, in 2WD the right front wheel should be disengaging and not spinning the front driveshaft or other wheel when you turn it. It should be completely free. 3-button has manual vacuum switch for axle lock directly on top of the transfer case. 4-button has vacuum switch for front axle lock electronically controlled and mounted on the center of the firewall above distributor. If the hoses are reversed on the 4-button switch, vacuum gets trapped and axle does not disengage unless the servo happens to bleed down enough. I had this 4-button problem myself.

 

Internet jocks will tell you strange stuff. It does stay at speed on the 4-button but only because the transfer case is designed that way, not the axle - and there is no purpose when in 2WD and axle is unlocked.