My son just purchased a '91 *-10 Blazer Tahoe 4x4 with I believe 247K on it (if that'* true). We just got a bunch of sleet and ice here in Arkansas and my son found out today that he does not have 4x4 high or low. I am not familiar with 4 wheel drives and was wondering if someone could give me a starting point on where and what to look for. When he tries to put it in 4 low, the shifter pops out of positon like it may be a linkage issue. Thanks.

The front diff is usually the issue with no 4wd. There is a cable that runs from the front diff to a vacuum actuator. Usually the cable is bad or the vacuum actuator is broken or not getting vacuum from the vacuum switch.

Is the transmission in NEUTRAL when putting into 4LO?

Yes, it is. Naturally, you should be in neutral on the steering column when shifting into 4wd, right? The 4wd shifting console has 2wd, 4wd high, neutral, and 4wd low.

No, some people do attempt to shift the transfer case while in D or R. Though the transfer case CAN shift from 2HI to 4HI, but it doesn't like/can't go from 2HI to 4LO or 4HI to 4LO.

On the newer models with pushbutton 4x4, the computer won't even attempt to shift from 2Hi to 4LO unless the vehicle is less than 2MPH and in NEUTRAL.