Hi. I just found the forum while trying to solve one of the many problems with my 1998 2dr Blazer. I have no four wheel drive at all any more. At first it would shift into 4Lo and 4Hi with no problems, but it would not shift back to 2HI. I finally got sick of it getting stuck ( Because chevy's genious idea of putting the switch right behinde the shifter that I always hit by accident grabbing the shifter) so I disconnected the switch all together. Now it is winter time, I just put a plow on it, and need the 4x4. I plugged the switch in and now all it will do is click the relays in the TCCM and that's it. no other noises. I replaced the vacuum switch on the transfer case and still nothing. It will click the relays like it wants to try to engage, and will do that if you push the button for either 4HI or 4Lo about 3 or 4 times, then will start only clicking once after that. I have no clue what to do. I never had a problem whats so ever with the push button 4x4 on my suburban, but both this blazer and my other old s10 PU had nothin but problems. If anyone could help me that would be greatly appreciated. I am really starting to get frustrated with the truck, it has been nothing but trouble scince we got stuck with it. Thank you, Mike

 

I forgot to add, when I'm driving up a hill or straining the motor when at 50-60 MPH, I can feel a shutter in the front end kind of like it is trying to engage the front end. I do know that it has a bad wheel bearing but I don't know if it is that, or the front dif. trying to engage. I also had to replace the heater controller because it had a vacuum leak at the vent controller switch. A gasket let go at the connection point to the vacuum lines. I also noticed a puddle of oil there too.

 

not sure on the 99, but I know on my 96 there is a vaccuum ball under the hood that has something to do with the vent control and 4x4. Mine broke and caused my 4 transfer case clunk into 4hi while driving at around 30mph. Not sure if that may be ur issue or something more but figured its worth looking into.

 

It sounds like it could be your vacuum actuator. I'm not sure though. Some of your simptoms are different than mine when I had 4wd problems.

I would suggest this...but I'm not sure it is your fix. But worth a try for only $25.

 

Ok, changed the fuse for the ATC and the vacuum actuator. Now it actually works great going into 4x4, but going back to 2hi it hesitates like it don't want to go, then blows the fuse, then clicks in. I don't know whats wrong with it but at least its is in 4x4 so I can plow with it. I'll deal with the other issue in the spring if I still have it. Thanks for the info.

 

Yeah, just be sure and have a pocketful of fuses.