Hello new to the board an have a very big problem with my trucks t case. I have a 2001 5.9 ram and when I shift it it to 4hi it has a very loud whine an grind to it. It is mostly from 5-35 mph it can be heard. Also when I take out of 4hi it takes a while to disengage almost have to stop the truck the punch the gas. Do you guy think it can be a bad shift fork? and what is the model of the case is it a 231?

 

You would hear whining noise from your t-case, but usually in 4Low.
I'm not sure why there is something grinding inside of the t-case.
Might have to take the t-case off and check.
First I would check level of your fluid inside the transfer case.
I would open the drain plug and see how the oil looks - Shavings, Smell etc.
If you have to refill it use good brand name of Automatic Transmission Fluid (ATF).
As far as the disengaging 4x4, once you shift bat to 2Hi shift your tranny into Reverse and roll back few inches. This should relief pressure on the drive line and disengage front axle much faster.

Hope this helps

 

welcome to df. yes it is an NP231. a common problem is a broken snap ring in the tailshaft area. this allows things to move around and and bang and grind and generally self destruct.

download the 01 service manual for diagrams and repair info.
http://www.rm-indy.com/wavefiles/2001ramsrvcmanual.zip

edit - its sort of normal for the axle to be sluggish to engage and disengage. stopping and backing up a few feet is the best way to get it to release. there's probably nothing wrong with the shift fork. check your vacuum level at the cad. service manual should tell you the spec.

 

Yeah its more of a whine than grind. I know its not the snap ring I know that noise I replaced them on my suburban a few times. When I bought the truck a couple months ago the owner said it wasnt drivin much it only had 60000 on the odometer. So I dumped the tranny fluid and tcase it was black like oil. Do you think this can be some what of the problem. And does any know were to get a used tcase or a good rebuilder.