1994 Chevy Blazer 4 wheel drive problem

SHARON67

MEMBER
1994 CHEVROLET BLAZER
6 CYL
4WD
AUTOMATIC
154,000 MILES

I wanted to know what would cause my 94 s10 blazer to seem to go into 4 wheel drive when I am driving on the highway. I tried to put it in 4 wheel drive and the lights on the dash wouldn't light and it seemed not to go in but then I was driving on the highway and heard a wirring noise and when I slowed down it seemed to be in 4 wheel drive then when I came to almost a stop I heard a clunking sound and the truck jumped a bit and then ran fine. I thought maybe it had been in and the light just didn't work to indicatr it but I tried pushing the button again and again no lights lit up and the truck was not in 4 wheel drive. (It slipped in the snow) I havent been back on the highway so I dont know if it will do the same thing again. Is there a sensor or something that may be causing this problem or is my 4 wheel drive messed up totally? It had been working fine before this! The truck has around 154000 miles on it and the rear diff. Has been replaced within the past few years. Please help with any suggestions and thanks!

1 Reply

MASTERTECHTIM

MECHANIC
4,750 POSTS

I assume you have electric shift 4wd. There could be a couple problems. There is a vacuum switch on the transfer case that sticks on 95 percent of these. This will cause the front differential to stay engaged. You will not be in 4wd because your transfer case is still in 2 wd. Also there is an electric motor on the side of the transfer case that engages the transfer case from 2wd to 4wd they are also very common for failing. You can try disconnecting the battery and reconnecting it. This will reset the transfercase control module. Then listen to the motor on the side of the transfer case while pressing it in and out of 4 wd. If you then hear it moving and you still dont have 4wd replace the vacuum switch on the transfer case. I hope this makes sense.