I have 2004 Blazer S10, 'electronic' transfer case (2hi,4hi,4low pushbuttons), 4wd was working fine no noise, over the course of the summer it started to make slight clunking noise (I rarely use 4wd, but drove it about a block a week in summer to keep it working ok). Now it is hit or miss whether I can engage 4hi while moving- sometimes yes, othertimes no, usually there is a clunking noise, but sometimes not. clunking is definitely coming from transfer case and not the front differential. From neutral/standstill I can always shift into 4lo, but a slight clunk, and from neutral/standstill I can always shift from 4lo to 4hi but a very loud clunk. I live in MN, so weather is now getting colder- seems like everything works better when weather is warm. Also on very cold days and when engine is not fully warmed up, clunking is intermittent, almost like it is trying to engage 4wd, and it does that for about 100-200 feet then usually ends up engaging.

Anyone have thoughts?

It has 70,000 miles and transfer case fluid has never been changed. I wanted to do that today as a starting point, but could not figure out what to use to get fluid back into the transfer case, so I did not start that task.

NP1 is one of the service codes listed on the tag in the glove compartment, I think that tells something about the kind of transfer case I have.

Thank-you for any advice from all of you experts out there, and happy thanksgiving!

 

Changing the fluid in the case is definately a good place to start. You can pick up a fluid transfer pump at alot of parts stores or on line at Harbor Freight Tools. It worked great for me. Just put one end in the bottle and the other in your case and start pumping until it is visible at the bottom of the fill hole. These things are almost impossible to clean out though so after you use it for trans. fluid only use it for trans fluid. Good luck and Happy Turkey Day.

 

Thanks for the tip about the hand pump, I picked one up at O'Reilly auto and had the fluid changed in about 10 min- worked real slick.

Unfortunately that did not help, I think I've got a serious issue, even tho it 'appears' to go into 4lo and 4hi from a standstill, the front wheels do not engage. Evert once in a while I can get it into 4hi, but I think something is broke or stripped in the front differential, as I have heard a couple of strange grinding and slipping type noises coming from there last night and today. Off the mechanic tomorrow for the (hopefully somewhat good) news.