Had this problem for awhile, doesn't seem to affect a whole lot but also switch it as soon as the grinding starts. I can floor it in town and have the rpm go up pretty high, and it's fine. (In 2wd) as soon as I go on the highway and go at those speeds, after or even during, there's a loud enough wining sound that can't be ignored, but I can switch it to 4x4 then to 2wd until it decides to slip again. Any ideas, haven't actually gone to a mechanic and mentioned it as I have been putting other things into the vehicle.

 

So, switching into and out of 4wd makes the noise stop?

First thing that comes to my mind is the front axle is being partially activated, and the noise is the gear teeth clashing in the coupler in the passenger side axle tube.

If you can, maybe check the front driveshaft when it's making the noise. It should spin freely in 2wd, if not, then the front axle is partially or fully engaged


Also, welcome to the forum!

 

same problem.
it's something with the input shaft seal between the transfer case and transmission.
doesn't really effect anything but i read that if you don't fix it it'll really mess you up.
theres a thread on here somewhere
i think it's called transmission leak.
i don't know,
i'll try to find it

 

Easy way to check is to pull the fill plug on the back of the tcase. There's two plugs, upper is fill, lower is drain.

The fluid level shouldn't be higher than the bottom of the fill plug. If you open it up, and a bunch of fluid comes pouring out, then the input seal on the tcase is leaking.

The np233 case is super easy to work on, but you'll have to drop the tcase to get to the input seal. Not difficult technically, but definitely a pain to wiggle in and out, plus it's fairly heavy

 

I have a 98 Blazer 4x4 also and it is doing the same thing as yours... I feel your pain! I am saving up the money to get it in the shop asap... Welcome to the Forum Tons of great people on here that are willing to help with any questions you might have on your truck to keep it on the road.