Literally just bought this 98 blazer... It had some issues which I had the dealer fix before I bought it as is, including a pesky vacuum leak behind the dash. He just replaced the head unit. On the ride home, at speed, the 2 hi started whining, which reduced to a grinding at low speed. O switched to 4 hi and the problem went away. The next morning, when I went to put it in reverse the first time, I noticed resistance. The second time the truck actually jumped in the front passenger side and made an awful noise that I was sure I broke something. I had to turn around and ride home in 4 lo, as the switches only blinked, but nothing would engage. I parked it for a bit, and magically it goes into 4 hi again, but I'm not moving this thing until I figure out the issue. I'm not much of a gear head, but everything I read initially pointed to a bad vacuum switch - now I'm not so sure with the big jump I I got out and looked to be sure that the wheel was still attached. I now can see some fluid has drained out in that area...I'm assuming the worse in that it is a bad transfer case, but I'd appreciate any input. I just spent a good sun of money on this (only 47k miles)...I'm not in a position to go way out of pocket after already paying for this in cash, but it is otherwise a nice vehicle. If there is any other info I need to put out there don't hesitate to ask.

 

The 4 wheel drive system on these Blazers is crap and unreliable. I have had issues with mine yearly since I bought it. If you don't have a service 4 wheel drive light on then you are going to have to make an educated guess at what the problem may be. It sounds like it could be the vacuum switch. I have replaced mine twice now so I know they are a problem. I am not sure if yours is on the transfer case or on the middle of the firewall above the distributer like mine. Check all your vacuum hoses to and from the switch and to the vacuum pot under the battery while you are at it.

 

sounds like your front actuator getting partial vacuum when in 2hi. Possibly it didnt completely shift into 2hi. Unplug and cap the vacuum line to the front axle actuator, or just take the cable off of it that goes to the front axle and see if it stops.

 

Update: I fooled around with it, but was unconvinced I had discovered the problem or fixed...so I took it to the dealership to have it checked out. Wouldn't you know the moment the tech climbs in and starts it up, it works like a charm Having never owned one, I've become well versed in reading other people's issues with this in the last 12 hours. After looking like a moron at the shop I can only hope that, unlike other people's issues, this magically stays fixed. The guy was lecturing me on how to utilize the 2/4 drive on the vehicle. He failed to comprehend that I never touched the damn thing until it started screaming like a banshee in the middle of the return trip home. Oh well, I suppose I should be thankful that it only cost me a day if work and not the thousands of dollars I already envisioned flushed down the drain

 

Update 2: I should add that once I removed the battery to inspect the actuator I discovered a harness down there to the left of the battery that had become disengaged. I plugged that back in...other than checking vacuum on the actuator under the battery I didn't do a whole hell if a lot, so I can only assume that this was what fixed it? I dunno - the symptoms seemed to jump all over the place. I had also left the battery disconnected for a good hour or so, and this might have helped. For now I'm just glad that it seems to be working just fine (fingers crossed)...