Hey there,
I have a 1996 dodge 2500 4x4 5.9L v8.

I have been having problems when I engage 4 wheel drive. What happens is a weird noise which sounds like rattling coming from underneath the truck. The sound is loudest when I let off the accelerator and the truck is coasting down the road.

When i first heard this I went under the truck and when I shook the front drive shaft i noticed it was very loose. I proceeded to change the 3 u-joints in the front drive shaft making the front drive shaft tight like it should be. After this I tried my 4x4 again and I still heard the same rattling sound. So the u-joints were not the problem.

The only other thing I can think of is a problem in the transfer case but I do not know enough about it to diagnose that.

Any help is appreciated. Thank you.
*Note- the 4x4 still works and engages with no problems. The only issue is the rattling noise.

Nick.

 

Do you have to be moving to hear the noise? Does the noise change pitch/volume in relation to vehicle speed? Engine speed?

Might try putting the truck up on jackstands, and see if you can isolate where the noise is coming from.

 

I do have to be moving to hear the noise. when going under 50km/h the noise is not very loud but noticeable and does not sounds healthy. once going about 80km/h it sounds bad and pretty loud. The sound is a low pitch sort of grumbling and rattling noise (hard to explain).
Putting it on jack stands is a good idea which I will eventually try.

 

if the noise is coming from the t-case, first check for a broken snap ring on the output shaft. lots of threads about that which a search will find.

if the snap ring is not broken - put it up on jack stands, crank it up and shift into 4wd and get your 4wd light on. then kill the motor, leave trans in neutral and turn the front wheels by hand... follow the noise.