4WD it wont engage. It sounds like it is. But its not locking.

LIZARDMAN

MEMBER
1996 CHEVROLET BLAZER
6 CYL
4WD
AUTOMATIC
160,000 MILES

I put my blazer into 4 wheel drive to pull a very large tree out of the road after a storm. It took around 15 min. Of hard pulling to remove the tree. I was proud of how good my little blazer did. A few months later.I tryed to put my blazer into 4 wheel drive. And it wont engage. It sounds like it is. But its not locking. What could have I broke by pulling that tree. It worked well pulling the tree. But when I took it out of 4 wheel drive, and then a few months later trying to use 4 wheel drive again. It wont engage. It sounds like it.I here the "DONK" when I press the 4x4 button. But no 4 wheel drive. Can you help? Any ideas? Thanks

1 Reply

SWILLIAMS

MECHANIC
597 POSTS

Could be many things. From a sticking vacuum switch on the transfer case to a broken transfer case or differential. You will need to start diagnostics on it. First check to see if the transfer case is engaging, You can do that by switching to 4X4 and then seeing if the front driveshaft is locked in. If it is then check the front axle interlock. It is cable controlled by a vacuum diaphragm located under the battery box. You can manually pull the cable and see if the front axle locks in. Just jack one side off the ground. In 2WD that wheel will turn, in 4X4 it won't. If those both check out OK then see if there is a vacuum signal to the 4X4 actuator when you switch it to 4wd. If not the valve on the transfer case may be bad OR a vacuum line going to it may be bad.